Anaerobic Pneumonia

Infectious Disease MONDO:0004649 Pathograph 19 Show in embeddings browser Bacterial Pneumonia Anaerobic Bacteria Infectious Disease

Anaerobic pneumonia is a polymicrobial bacterial pneumonia in which oral or upper-airway anaerobes reach the lower respiratory tract, establish mixed anaerobic-aerobic infection, and can progress through necrotizing pneumonia to cavitary lung abscess and pleural empyema. The entry is scoped to MONDO's agent-defined term: it overlaps heavily with aspiration pneumonia, but aspiration pneumonia also includes chemical pneumonitis and aerobic Gram-negative infections in which anaerobes are not the dominant mechanism.

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6
Pathophys.
6
Phenotypes
19
Pathograph
4
Medical Actions
1
Deep Research
🏷

Classifications

Harrison's Part
INFECTIOUS DISEASES
⚙

Pathophysiology

6
Oropharyngeal Anaerobe Aspiration
Impaired airway defense, such as alcoholism or post-stroke dysphagia, permits infectious material from the oropharyngeal cavity and upper respiratory tract to enter dependent lower-airway segments.
lung UBERON:0002048 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in lung (UBERON:0002048). UBERON:0002048 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Polymicrobial Anaerobic-Aerobic Lung Infection Aspirated oral and upper-airway material seeds the lower respiratory tract with mixed anaerobic and aerobic flora.
Show evidence (1 reference)
PMID:20477271 SUPPORT REVIEW SYNTHESIS Other
"Pneumonia and primary lung abscesses may result from aspiration of infectious material from the oropharyngeal cavity and the upper respiratory tract."
Supports oropharyngeal aspiration as the initiating route into the lung.
Polymicrobial Anaerobic-Aerobic Lung Infection
The infected lung or pleural space usually contains several anaerobic species, often with coexisting nonanaerobes, so anaerobic pneumonia is better modeled as a community infection than as a single-species pneumonia.
lung UBERON:0002048 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in lung (UBERON:0002048). UBERON:0002048 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Prevotella-Enhanced Alveolar Adhesion In model systems, Prevotella products increase lower-airway bacterial adhesion, suggesting one mechanism by which oral anaerobes can amplify coinfecting bacterial pneumonia.
Fever Mixed anaerobic-aerobic infection in the lung can produce systemic febrile illness.
Show evidence (2 references)
PMID:8324128 SUPPORT Human Clinical
"cultures yielded an average of 3.0 anaerobes and 0.6 nonanaerobes per specimen."
Quantifies the polymicrobial anaerobe-heavy composition of anaerobic pleuropulmonary infection specimens.
PMID:12959026 SUPPORT Human Clinical
"Lower respiratory infections are usually either polymicrobial or mixed anaerobic-aerobic infections."
Describes the mixed anaerobic-aerobic bacteriology of lower respiratory anaerobic infections.
Prevotella-Enhanced Alveolar Adhesion
Products from the oral anaerobe Prevotella intermedia can amplify pneumococcal adhesion to human alveolar epithelial cells together with platelet-activating-factor receptor expression. This is modeled as indirect support because the experiment used a pneumococcal coinfection rather than a purely anaerobic pneumonia.
epithelial cell of lower respiratory tract CL:0002632 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves epithelial cell of lower respiratory tract (CL:0002632). CL:0002632 is a cell type from the Cell Ontology.
adhesion of symbiont to host GO:0044406 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased adhesion of symbiont to host (GO:0044406). GO:0044406 is a biological process from the Gene Ontology. ↑ INCREASED
Downstream
Anaerobe-Amplified Pneumonic Inflammation Higher lower-airway bacterial adhesion can increase the lung bacterial burden that drives host cytokine release.
Show evidence (1 reference)
PMID:24478074 SUPPORT INDIRECT In Vitro
"In A549 cells, PiSup increased pneumococcal adhesion and PAFR transcript levels."
Shows that Prevotella products increase pneumococcal adhesion to human alveolar epithelial cells and induce the host receptor implicated in that adhesion; the assay is indirect because it tests pneumococcal adhesion under Prevotella supernatant exposure.
Anaerobe-Amplified Pneumonic Inflammation
In mouse coinfection experiments, Prevotella intermedia products intensified pneumococcal pneumonia, bacterial burden, and alveolar cytokine production. This supports an anaerobe-mediated inflammatory amplification arm rather than a direct human anaerobic-pneumonia mechanism.
inflammatory response GO:0006954 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased inflammatory response (GO:0006954). GO:0006954 is a biological process from the Gene Ontology. ↑ INCREASED
lung UBERON:0002048 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in lung (UBERON:0002048). UBERON:0002048 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Necrotizing Cavitary Lung Destruction Sustained mixed bacterial growth and cytokine-rich inflammation are upstream of the tissue destruction that distinguishes cavitary anaerobic disease from uncomplicated pneumonia.
Show evidence (1 reference)
PMID:24478074 SUPPORT INDIRECT Model Organism
"Mice inoculated with S. pneumoniae plus PiSup exhibited a significantly lower survival rate, higher bacterial loads in the lungs, spleen, and blood, and higher inflammatory cytokine levels in the bronchoalveolar lavage fluid (macrophage inflammatory protein 2 and tumor necrosis factor alpha)..."
Demonstrates Prevotella-mediated inflammatory amplification in a pneumococcal pneumonia model, an indirect model for oral-anaerobe synergy in the lower airway.
Necrotizing Cavitary Lung Destruction
Untreated or severe anaerobic infection can progress over days from aspiration pneumonia to necrotizing pneumonia and pulmonary abscess, with foul-smelling putrid sputum and cavitary disease as delayed manifestations.
inflammatory response GO:0006954 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased inflammatory response (GO:0006954). GO:0006954 is a biological process from the Gene Ontology. ↑ INCREASED
lung UBERON:0002048 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in lung (UBERON:0002048). UBERON:0002048 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Lung Abscess Necrotizing anaerobic pneumonia destroys lung parenchyma and forms cavitary pulmonary abscesses.
Productive Cough Cavitary anaerobic disease can drain foul, putrid material into the airway and cause productive cough.
Pleural Extension of Infection Peripheral or ruptured cavitary infection can extend through the pleura, creating empyema or bronchopleural fistula.
Hemoptysis Cavitary lung abscess can erode inflamed airway and vascular tissue, producing hemoptysis in some anaerobic abscess presentations.
Chest pain Cavitary and pleural inflammation can manifest with chest pain.
Show evidence (1 reference)
PMID:20477271 SUPPORT REVIEW SYNTHESIS Other
"Necrotizing pneumonia, pulmonary abscesses and the characteristic, foul-smelling, putrid discharge only occur 8-14 days after the initial aspiration event."
Links aspiration-associated cavitary anaerobic disease to necrotizing pneumonia, lung abscess, and the delayed putrid sputum manifestation.
Pleural Extension of Infection
Cavitary lung infection can involve the pleural surface or rupture into the pleural space, producing empyema and, in severe cases, bronchopleural fistula that requires source control.
pleura UBERON:0000977 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in pleura (UBERON:0000977). UBERON:0000977 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Pleural Empyema Pleural extension seeds infected fluid in the pleural cavity and produces empyema.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Anaerobic Pneumonia Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
●

Phenotypes

6
Immune 1
Lung Abscess HP:0025044 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Lung abscess (HP:0025044). HP:0025044 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:20477271 SUPPORT REVIEW SYNTHESIS Other
"Necrotizing pneumonia, pulmonary abscesses and the characteristic, foul-smelling, putrid discharge only occur 8-14 days after the initial aspiration event."
Places pulmonary abscess in the time course of aspiration-associated anaerobic cavitary disease.
Metabolism 2
Fever HP:0001945 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Fever (HP:0001945). HP:0001945 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:41886424 SUPPORT Human Clinical
"Systemic symptoms such as fever (91%) and hypoactivity (91%) were common."
Reports fever in a pediatric lung-abscess cohort, grounding fever as a common systemic feature of cavitary pneumonia while not claiming that all pediatric abscesses were anaerobic.
Pleural Empyema HP:0011919 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Pleural empyema (HP:0011919). HP:0011919 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:23398871 SUPPORT REVIEW SYNTHESIS Other
"These bacteria are relatively common in selected types of lung infections including aspiration pneumonia, lung abscess, necrotizing pneumonia and emphyema."
Names pleural empyema among the selected lung infections where anaerobes are relatively common; the abstract misspells empyema as "emphyema".
Respiratory 2
Productive Cough HP:0031245 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Productive cough (HP:0031245). HP:0031245 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:41886424 SUPPORT Human Clinical
"Cough was reported in 87% of cases, with varying patterns (dry, wet, or both)."
Establishes cough as a frequent lung-abscess feature, with wet/productive cough represented among the reported patterns.
PMID:20477271 SUPPORT REVIEW SYNTHESIS Other
"Necrotizing pneumonia, pulmonary abscesses and the characteristic, foul-smelling, putrid discharge only occur 8-14 days after the initial aspiration event."
Supports the anaerobic-specific putrid sputum quality that can accompany productive cough after cavitation.
Hemoptysis HP:0002105 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hemoptysis (HP:0002105). HP:0002105 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:41054501 SUPPORT Human Clinical
"The primary clinical manifestations were nonspecific respiratory symptoms, including cough, fever, chest pain, and hemoptysis."
Documents hemoptysis in a small mNGS-confirmed Tannerella forsythia lung abscess series.
Constitutional 1
Chest pain HP:0100749 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Chest pain (HP:0100749). HP:0100749 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:41054501 SUPPORT Human Clinical
"The primary clinical manifestations were nonspecific respiratory symptoms, including cough, fever, chest pain, and hemoptysis."
Documents chest pain in a small mNGS-confirmed Tannerella forsythia lung abscess series.
💊

Medical Actions

4
Clindamycin and beta-lactam/beta-lactamase-inhibitor therapy
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: clindamycin CHEBI:3745 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses clindamycin (CHEBI:3745). CHEBI:3745 is a therapeutic agent from Chemical Entities of Biological Interest. amoxicillin CHEBI:2676 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses amoxicillin (CHEBI:2676). CHEBI:2676 is a therapeutic agent from Chemical Entities of Biological Interest. ampicillin CHEBI:28971 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses ampicillin (CHEBI:28971). CHEBI:28971 is a therapeutic agent from Chemical Entities of Biological Interest.
Platform: Small molecule
Antibiotic therapy must cover anaerobes and frequent aerobic copathogens; clindamycin, amoxicillin-clavulanate, and ampicillin-sulbactam are named anti-anaerobic options, while metronidazole monotherapy is insufficient for mixed anaerobic-aerobic infection.
Mechanism Target:
INHIBITS Polymicrobial Anaerobic-Aerobic Lung Infection — Anti-anaerobic antibiotics treat the mixed anaerobic-aerobic bacterial burden in the lung or pleural space.
Show evidence (2 references)
PMID:23398871 SUPPORT REVIEW SYNTHESIS Other
"Preferred antibiotics for these infections based on clinical experience are clindamycin and any betalactam-betalactamase inhibitor."
Names clindamycin and beta-lactam/beta-lactamase inhibitor therapy as experience-based preferred antibiotic options.
PMID:12959026 SUPPORT Human Clinical
"Treatment includes an antibiotics regimen with an agent active against anaerobic and aerobic bacteria (therapy with 2 or 3 antimicrobial drugs)."
Supports broad antibacterial coverage rather than anaerobe-only treatment for mixed lower-respiratory anaerobic infection.
Moxifloxacin therapy for aspiration pneumonia and primary lung abscess
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: moxifloxacin CHEBI:63611 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses moxifloxacin (CHEBI:63611). CHEBI:63611 is a therapeutic agent from Chemical Entities of Biological Interest.
Platform: Small molecule
Moxifloxacin is a newer fluoroquinolone with anaerobic activity that has shown clinical efficacy similar to clindamycin and aminopenicillin/ beta-lactamase-inhibitor regimens in aspiration pneumonia and primary lung abscess.
Mechanism Target:
INHIBITS Polymicrobial Anaerobic-Aerobic Lung Infection — Antibacterial therapy suppresses the mixed bacterial burden that drives anaerobe-dominant aspiration pneumonia and primary lung abscess.
Show evidence (1 reference)
PMID:20477271 SUPPORT REVIEW SYNTHESIS Other
"Aminopenicillins/beta-lactamase inhibitors, newer fluoroquinolones with anaerobic activity (moxifloxacin) and clindamycin have demonstrated equal clinical efficacy in the treatment of aspiration pneumonia and primary lung abscess."
Names moxifloxacin among regimens with demonstrated efficacy in aspiration pneumonia and primary lung abscess.
Abscess and empyema drainage
Action: DrainageNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Drainage (NCIT:C50434). NCIT:C50434 is a clinical intervention from the NCI Thesaurus. NCIT:C50434
Platform: Other
Percutaneous, tube, or thoracoscopic drainage provides source control for infected lung abscesses or empyema collections that are not controlled by pharmacotherapy alone.
Mechanism Target:
INHIBITS Necrotizing Cavitary Lung Destruction — Source-control procedures drain abscesses or infected pleural collections that do not resolve with pharmacotherapy alone.
INHIBITS Pleural Extension of Infection — Drainage removes loculated infected pleural fluid and reduces pleural inflammatory burden.
Show evidence (1 reference)
PMID:20223322 SUPPORT Human Clinical
"Thoracoscopic abscess drainage is associated with minimal morbidity and may result in faster recovery and a shorter course of antibiotics."
Supports thoracoscopic drainage as a source-control option for lung abscesses with empyema in a pediatric surgical series.
Thoracotomy and decortication for refractory empyema
Action: Surgical ProcedureNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Surgical Procedure (NCIT:C15329). NCIT:C15329 is a clinical intervention from the NCI Thesaurus. NCIT:C15329
Platform: Surgery
Empyema that remains loculated or refractory after initial drainage can require thoracotomy and decortication.
Mechanism Target:
INHIBITS Pleural Extension of Infection — Decortication surgically clears organized infected pleural material when tube drainage is insufficient.
Show evidence (2 references)
PMID:20477271 SUPPORT REVIEW SYNTHESIS Other
"Since antibiotics can provide cure in 80-90% of cases, surgical procedures are limited to severe complications, such as pleural empyema."
Supports reserving surgery for severe complications after most cases are managed medically.
PMID:22610800 SUPPORT Human Clinical
"Fourteen out of seventeen (82.35%) of the patients who were initially treated with thoracocentesis or tube thoracostomy eventually needed thoracotomy."
Documents escalation from initial drainage to thoracotomy in a retrospective empyema thoracis surgical cohort.
🌍

Environmental Factors

3
Depressed consciousness and esophageal dysfunction
Alcohol, sedative exposure, stroke-associated mental-status compromise, and esophageal dysfunction increase the chance that anaerobe-rich oropharyngeal or gastric contents enter the lower respiratory tract.
Show evidence (1 reference)
PMID:11695090 SUPPORT REVIEW SYNTHESIS Other
"A compromised mental status (e.g. alcoholism, sedatives, stroke) and esophageal dysfunction (e.g. herniation, vomiting) are important risk factors."
Supports impaired consciousness and esophageal dysfunction as clinical contexts that predispose to aspiration and abscess-forming pneumonia.
Mechanism Target:
PREDISPOSES Oropharyngeal Anaerobe Aspiration — Loss of ordinary airway protection permits aspiration, the initiating event for anaerobe-dominant primary lung abscess.
Show evidence (1 reference)
PMID:11695090 SUPPORT REVIEW SYNTHESIS Other
"A compromised mental status (e.g. alcoholism, sedatives, stroke) and esophageal dysfunction (e.g. herniation, vomiting) are important risk factors."
Names depressed consciousness and esophageal dysfunction as risk factors for aspiration-driven primary lung abscess.
Swallowing dysfunction and impaired cough reflex
Dysphagia, degenerative neurologic disease, and an impaired cough reflex weaken airway clearance and favor aspiration of colonized oropharyngeal secretions.
Show evidence (1 reference)
PMID:39536943 SUPPORT REVIEW SYNTHESIS Other
"Aspiration pneumonia refers to the process of alveolar inflammation induced by the inhalation of oropharyngeal secretions into the lower respiratory tract."
Frames aspiration pneumonia as inhalation of oropharyngeal secretions into the lower airway.
Mechanism Target:
PREDISPOSES Oropharyngeal Anaerobe Aspiration — Impaired swallowing and cough clearance make inhalation of oropharyngeal secretions into alveoli more likely.
Show evidence (1 reference)
PMID:39536943 SUPPORT REVIEW SYNTHESIS Other
"Predisposing factors comprise swallowing dysfunction, impaired cough reflex, and degenerative neurological diseases."
Identifies the airway-protection failures that predispose to aspiration pneumonia.
Oral frailty and poor oral health
Oral frailty and oral disease increase the reservoir of oral anaerobes available for aspiration into dependent lung segments.
Show evidence (1 reference)
PMID:41054501 SUPPORT Human Clinical
"All patients had oral diseases, and 75% were long-term smokers."
Reports oral disease in a small anaerobic Tannerella forsythia lung abscess series diagnosed by bronchoalveolar-lavage mNGS.
Mechanism Target:
PREDISPOSES Oropharyngeal Anaerobe Aspiration — Poor oral health expands the anaerobic oral burden, which can then be aspirated when swallowing and airway defenses fail.
Show evidence (1 reference)
PMID:42548261 SUPPORT Human Clinical
"AP was associated with cumulative oral frailty-related conditions and meal positioning among residents at high risk of malnutrition in long-term care facilities."
Connects cumulative oral frailty to aspiration pneumonia in a long-term-care cohort.
🔬

Diagnosis

3
Bronchoalveolar Lavage Metagenomic Sequencing
Comprehensive metagenomic next-generation sequencing of bronchoalveolar lavage fluid can detect anaerobic sequences that targeted panels and routine culture miss, but the result must be interpreted against aspiration risk and oral-disease context because oral anaerobes can also be colonizers.
metagenomic next-generation sequencing of bronchoalveolar lavage fluid NCIT:C101293 NCI Thesaurus (NCIT)
Show evidence (1 reference)
PMID:42445473 SUPPORT Human Clinical
"In both cases, tNGS was unable to detect anaerobic pathogens due to the limited scope of anaerobic bacterial targets in commercial panels. In contrast, comprehensive mNGS, when correctly interpreted in conjunction with clinical context, can detect anaerobic sequences."
Supports comprehensive mNGS as a diagnostic route for anaerobic pneumonia when targeted sequencing and routine testing miss anaerobes.
Chest CT for cavitary lung lesions
Chest CT characterizes cavitary lesions, air-fluid levels, and necrotizing pneumonia or lung abscess patterns when anaerobic pneumonia has progressed to cavitation.
chest computed tomography
Show evidence (2 references)
PMID:41688916 SUPPORT Human Clinical
"Chest CT revealed a cavitary lesion with an air-fluid level in the right lower lobe."
Shows the classic CT appearance of a lung abscess with an air-fluid level.
PMID:42487366 SUPPORT Human Clinical
"Non-contrast CT is a valuable diagnostic tool for pediatric cavitary pulmonary lesions, particularly necrotizing pneumonia and hydatid cysts."
Supports CT as a tool for evaluating pediatric cavitary pulmonary lesions, including necrotizing pneumonia and lung abscess in the study differential.
Protected lower-airway anaerobic sampling
Anaerobic culture requires lower-airway, abscess, or pleural samples that minimize contamination by ubiquitous oral anaerobes; sputum is not reliable for anaerobic culture.
protected lower airway sampling
Show evidence (2 references)
PMID:11695090 SUPPORT REVIEW SYNTHESIS Other
"Bacteriological sampling should be performed using protected specimen brushing (PSB) technique."
Recommends protected specimen brushing for bacteriologic sampling in abscess-forming aspiration pneumonia.
PMID:12959026 SUPPORT Human Clinical
"Appropriatte specimens include: pus, purulent fluid, biopsy specimen of lung, transtracheal aspirates and bronchoalveolar lavage (BAL)."
Lists uncontaminated lower-airway or purulent samples appropriate for anaerobic respiratory infection diagnosis.
🦠

Infectious Agent

4
Prevotella
Prevotella species are recurring oral anaerobes in anaerobic pleuropulmonary infection; pigmented and nonpigmented Prevotella species were among the most commonly encountered anaerobes in a pleural-fluid-heavy bacteriology series.
Prevotella NCBITaxon:838 NCBI Taxonomy (NCBITaxon)
Show evidence (1 reference)
PMID:8324128 SUPPORT Human Clinical
"The most commonly encountered anaerobes were pigmented Prevotella species, nonpigmented Prevotella species, Fusobacterium nucleatum, Peptostreptococcus species, and Bacteroides species."
Identifies Prevotella as a frequent anaerobe recovered from anaerobic pleuropulmonary infection specimens.
Fusobacterium nucleatum
Fusobacterium nucleatum is an oral anaerobe repeatedly isolated from anaerobic lower-respiratory infection and reported in mNGS-confirmed anaerobic pneumonia.
Fusobacterium nucleatum NCBITaxon:851 NCBI Taxonomy (NCBITaxon)
Show evidence (1 reference)
PMID:8324128 SUPPORT Human Clinical
"The most commonly encountered anaerobes were pigmented Prevotella species, nonpigmented Prevotella species, Fusobacterium nucleatum, Peptostreptococcus species, and Bacteroides species."
Names Fusobacterium nucleatum among the common anaerobes in pleuropulmonary infection specimens.
Peptostreptococcus
Peptostreptococcus species are Gram-positive anaerobic cocci that appear in the recurring anaerobic respiratory-pathogen set.
Peptostreptococcus NCBITaxon:1257 NCBI Taxonomy (NCBITaxon)
Show evidence (1 reference)
PMID:12959026 SUPPORT Human Clinical
"Peptostreptococcus, Fusobacterium, Prevotella and Bacteroides are the most common anaerobes."
Lists Peptostreptococcus among common anaerobes in lower respiratory anaerobic infections.
Bacteroides
Bacteroides species are part of the recurrent oral/upper-airway anaerobic flora recovered from anaerobic respiratory infections.
Bacteroides NCBITaxon:816 NCBI Taxonomy (NCBITaxon)
Show evidence (1 reference)
PMID:12959026 SUPPORT Human Clinical
"Peptostreptococcus, Fusobacterium, Prevotella and Bacteroides are the most common anaerobes."
Lists Bacteroides among common anaerobes in lower respiratory anaerobic infections.
↔️

Transmission

1
Aspiration of colonized oropharyngeal secretions and gastric contents
Anaerobic pneumonia is acquired endogenously, not from another person: the inoculum is the patient's own oropharyngeal flora, carried into the lower respiratory tract when oral or upper gastrointestinal contents are inhaled past a failing airway defence. Because the anaerobes are oral commensals, the route and the reservoir are the same mouth, which is why poor oral hygiene raises the size of the inoculum rather than introducing a new organism, and why the anaerobe-dominant infections appear in patients whose swallowing or consciousness is impaired.
There is no person-to-person route and no environmental or vector reservoir for this entry. The host factors that permit aspiration are modelled separately in `environmental:`; this block records only the route by which the organisms reach the lung.
Show evidence (4 references)
PMID:39536943 SUPPORT REVIEW SYNTHESIS Other
"Aspiration pneumonia refers to the process of alveolar inflammation induced by the inhalation of oropharyngeal secretions into the lower respiratory tract."
Defines the route: inhalation of oropharyngeal secretions into the lower respiratory tract.
PMID:20477271 SUPPORT REVIEW SYNTHESIS Other
"Pneumonia and primary lung abscesses may result from aspiration of infectious material from the oropharyngeal cavity and the upper respiratory tract."
Names the oropharyngeal cavity and upper respiratory tract as the source of the aspirated inoculum.
PMID:11695090 SUPPORT REVIEW SYNTHESIS Other
"Aspiration of oro-pharyngeal secretions and gastric content is the most frequent cause of formation of primary lung abscess."
Adds gastric content to the aspirated material and establishes that this route is the usual cause of the cavitary form.
+ 1 more reference
{ }

Source YAML

click to show 
name: Anaerobic Pneumonia
creation_date: "2026-09-26T02:28:16Z"
category: Infectious Disease
description: >-
  Anaerobic pneumonia is a polymicrobial bacterial pneumonia in which oral or
  upper-airway anaerobes reach the lower respiratory tract, establish
  mixed anaerobic-aerobic infection, and can progress through necrotizing
  pneumonia to cavitary lung abscess and pleural empyema. The entry is scoped to
  MONDO's agent-defined term: it overlaps heavily with aspiration pneumonia, but
  aspiration pneumonia also includes chemical pneumonitis and aerobic
  Gram-negative infections in which anaerobes are not the dominant mechanism.
disease_term:
  preferred_term: anaerobic pneumonia
  term:
    id: MONDO:0004649
    label: anaerobic pneumonia
parents:
- Bacterial Pneumonia
- Anaerobic Bacteria Infectious Disease
synonyms:
- pneumonia due to anaerobic bacteria
- anaerobic pleuropulmonary infection
- anaerobic lung infection
classifications:
  harrisons_chapter:
  - classification_value: INFECTIOUS_DISEASES
infectious_agent:
- name: Prevotella
  infectious_agent_term:
    preferred_term: Prevotella
    term:
      id: NCBITaxon:838
      label: Prevotella
  description: >-
    Prevotella species are recurring oral anaerobes in anaerobic
    pleuropulmonary infection; pigmented and nonpigmented Prevotella species
    were among the most commonly encountered anaerobes in a pleural-fluid-heavy
    bacteriology series.
  evidence:
  - reference: PMID:8324128
    reference_title: "Bacteriology of anaerobic pleuropulmonary infections: preliminary report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The most commonly encountered anaerobes were pigmented Prevotella species,
      nonpigmented Prevotella species, Fusobacterium nucleatum, Peptostreptococcus
      species, and Bacteroides species.
    explanation: >-
      Identifies Prevotella as a frequent anaerobe recovered from anaerobic
      pleuropulmonary infection specimens.
- name: Fusobacterium nucleatum
  infectious_agent_term:
    preferred_term: Fusobacterium nucleatum
    term:
      id: NCBITaxon:851
      label: Fusobacterium nucleatum
  description: >-
    Fusobacterium nucleatum is an oral anaerobe repeatedly isolated from
    anaerobic lower-respiratory infection and reported in mNGS-confirmed
    anaerobic pneumonia.
  evidence:
  - reference: PMID:8324128
    reference_title: "Bacteriology of anaerobic pleuropulmonary infections: preliminary report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The most commonly encountered anaerobes were pigmented Prevotella species,
      nonpigmented Prevotella species, Fusobacterium nucleatum, Peptostreptococcus
      species, and Bacteroides species.
    explanation: >-
      Names Fusobacterium nucleatum among the common anaerobes in
      pleuropulmonary infection specimens.
- name: Peptostreptococcus
  infectious_agent_term:
    preferred_term: Peptostreptococcus
    term:
      id: NCBITaxon:1257
      label: Peptostreptococcus
  description: >-
    Peptostreptococcus species are Gram-positive anaerobic cocci that appear in
    the recurring anaerobic respiratory-pathogen set.
  evidence:
  - reference: PMID:12959026
    reference_title: "[Incidence of anaerobic bacteria in respiratory tract infections]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Peptostreptococcus, Fusobacterium, Prevotella and Bacteroides are the most
      common anaerobes.
    explanation: >-
      Lists Peptostreptococcus among common anaerobes in lower respiratory
      anaerobic infections.
- name: Bacteroides
  infectious_agent_term:
    preferred_term: Bacteroides
    term:
      id: NCBITaxon:816
      label: Bacteroides
  description: >-
    Bacteroides species are part of the recurrent oral/upper-airway anaerobic
    flora recovered from anaerobic respiratory infections.
  evidence:
  - reference: PMID:12959026
    reference_title: "[Incidence of anaerobic bacteria in respiratory tract infections]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Peptostreptococcus, Fusobacterium, Prevotella and Bacteroides are the most
      common anaerobes.
    explanation: >-
      Lists Bacteroides among common anaerobes in lower respiratory anaerobic
      infections.

transmission:
- name: Aspiration of colonized oropharyngeal secretions and gastric contents
  description: >-
    Anaerobic pneumonia is acquired endogenously, not from another person: the
    inoculum is the patient's own oropharyngeal flora, carried into the lower
    respiratory tract when oral or upper gastrointestinal contents are inhaled past
    a failing airway defence. Because the anaerobes are oral commensals, the route
    and the reservoir are the same mouth, which is why poor oral hygiene raises the
    size of the inoculum rather than introducing a new organism, and why the
    anaerobe-dominant infections appear in patients whose swallowing or
    consciousness is impaired.
  notes: >-
    There is no person-to-person route and no environmental or vector reservoir for
    this entry. The host factors that permit aspiration are modelled separately in
    `environmental:`; this block records only the route by which the organisms reach
    the lung.
  evidence:
  - reference: PMID:39536943
    reference_title: >-
      "Bacteriology of Aspiration Pneumonia: The Lung Microbiome and the Changing
      Microbial Etiology."
    supports: SUPPORT
    quote_role: REVIEW_SYNTHESIS
    evidence_source: OTHER
    snippet: >-
      Aspiration pneumonia refers to the process of alveolar inflammation induced by
      the inhalation of oropharyngeal secretions into the lower respiratory tract.
    explanation: >-
      Defines the route: inhalation of oropharyngeal secretions into the lower
      respiratory tract.
  - reference: PMID:20477271
    reference_title: >-
      "Aspiration pneumonia and primary lung abscess: diagnosis and therapy of an
      aerobic or an anaerobic infection?"
    supports: SUPPORT
    quote_role: REVIEW_SYNTHESIS
    evidence_source: OTHER
    snippet: >-
      Pneumonia and primary lung abscesses may result from aspiration of infectious
      material from the oropharyngeal cavity and the upper respiratory tract.
    explanation: >-
      Names the oropharyngeal cavity and upper respiratory tract as the source of the
      aspirated inoculum.
  - reference: PMID:11695090
    reference_title: "[Diagnosis and therapy of abscess forming pneumonia]."
    supports: SUPPORT
    quote_role: REVIEW_SYNTHESIS
    evidence_source: OTHER
    snippet: >-
      Aspiration of oro-pharyngeal secretions and gastric content is the most frequent
      cause of formation of primary lung abscess.
    explanation: >-
      Adds gastric content to the aspirated material and establishes that this route
      is the usual cause of the cavitary form.
  - reference: PMID:42445473
    reference_title: >-
      "Detection Blind Spots in Microbial Culture, tNGS, and mNGS: Anaerobic Bacterial
      Infections in the Lung-A Retrospective Analysis of Two Cases."
    supports: SUPPORT
    quote_role: BACKGROUND
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Aspiration pneumonia, caused by selective obligate anaerobes like oral commensal
      bacteria, occurs when oral or upper digestive tract contents are inhaled
    explanation: >-
      States that the responsible anaerobes are oral commensals, which is what makes
      this route endogenous rather than a transmission from an external source. The
      quote is the introduction of a two-case analysis stating the established route,
      so it is marked BACKGROUND.
environmental:
- name: Depressed consciousness and esophageal dysfunction
  description: >-
    Alcohol, sedative exposure, stroke-associated mental-status compromise, and
    esophageal dysfunction increase the chance that anaerobe-rich oropharyngeal
    or gastric contents enter the lower respiratory tract.
  influences_mechanisms:
  - target: Oropharyngeal Anaerobe Aspiration
    environmental_effect: PREDISPOSES
    causal_link_type: DIRECT
    description: >-
      Loss of ordinary airway protection permits aspiration, the initiating
      event for anaerobe-dominant primary lung abscess.
    evidence:
    - reference: PMID:11695090
      reference_title: "[Diagnosis and therapy of abscess forming pneumonia]."
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      snippet: >-
        A compromised mental status (e.g. alcoholism, sedatives, stroke) and
        esophageal dysfunction (e.g. herniation, vomiting) are important risk
        factors.
      explanation: >-
        Names depressed consciousness and esophageal dysfunction as risk
        factors for aspiration-driven primary lung abscess.
  evidence:
  - reference: PMID:11695090
    reference_title: "[Diagnosis and therapy of abscess forming pneumonia]."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      A compromised mental status (e.g. alcoholism, sedatives, stroke) and
      esophageal dysfunction (e.g. herniation, vomiting) are important risk
      factors.
    explanation: >-
      Supports impaired consciousness and esophageal dysfunction as clinical
      contexts that predispose to aspiration and abscess-forming pneumonia.
- name: Swallowing dysfunction and impaired cough reflex
  description: >-
    Dysphagia, degenerative neurologic disease, and an impaired cough reflex
    weaken airway clearance and favor aspiration of colonized oropharyngeal
    secretions.
  influences_mechanisms:
  - target: Oropharyngeal Anaerobe Aspiration
    environmental_effect: PREDISPOSES
    causal_link_type: DIRECT
    description: >-
      Impaired swallowing and cough clearance make inhalation of oropharyngeal
      secretions into alveoli more likely.
    evidence:
    - reference: PMID:39536943
      reference_title: "Bacteriology of Aspiration Pneumonia: The Lung Microbiome and the Changing Microbial Etiology."
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      snippet: >-
        Predisposing factors comprise swallowing dysfunction, impaired cough
        reflex, and degenerative neurological diseases.
      explanation: >-
        Identifies the airway-protection failures that predispose to aspiration
        pneumonia.
  evidence:
  - reference: PMID:39536943
    reference_title: "Bacteriology of Aspiration Pneumonia: The Lung Microbiome and the Changing Microbial Etiology."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Aspiration pneumonia refers to the process of alveolar inflammation
      induced by the inhalation of oropharyngeal secretions into the lower
      respiratory tract.
    explanation: >-
      Frames aspiration pneumonia as inhalation of oropharyngeal secretions into
      the lower airway.
- name: Oral frailty and poor oral health
  description: >-
    Oral frailty and oral disease increase the reservoir of oral anaerobes
    available for aspiration into dependent lung segments.
  influences_mechanisms:
  - target: Oropharyngeal Anaerobe Aspiration
    environmental_effect: PREDISPOSES
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Poor oral health expands the anaerobic oral burden, which can then be
      aspirated when swallowing and airway defenses fail.
    evidence:
    - reference: PMID:42548261
      reference_title: Oral Frailty and Meal Positioning Associated With Aspiration Pneumonia in Long-Term Care Residents at High Risk of Malnutrition.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        AP was associated with cumulative oral frailty-related conditions and
        meal positioning among residents at high risk of malnutrition in
        long-term care facilities.
      explanation: >-
        Connects cumulative oral frailty to aspiration pneumonia in a
        long-term-care cohort.
  evidence:
  - reference: PMID:41054501
    reference_title: "Metagenomic Next-Generation Sequencing Reveals Tannerella forsythia in Lung Abscesses: A Retrospective Case Series Linking Smoking, Oral Health, and Diagnostic Challenges."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All patients had oral diseases, and 75% were long-term smokers.
    explanation: >-
      Reports oral disease in a small anaerobic Tannerella forsythia lung
      abscess series diagnosed by bronchoalveolar-lavage mNGS.

pathophysiology:
- name: Oropharyngeal Anaerobe Aspiration
  role: trigger
  description: >-
    Impaired airway defense, such as alcoholism or post-stroke dysphagia,
    permits infectious material from the oropharyngeal cavity and upper
    respiratory tract to enter dependent lower-airway segments.
  biological_scale: ORGANISM
  locations:
  - preferred_term: lung
    term:
      id: UBERON:0002048
      label: lung
  evidence:
  - reference: PMID:20477271
    reference_title: "Aspiration pneumonia and primary lung abscess: diagnosis and therapy of an aerobic or an anaerobic infection?"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Pneumonia and primary lung abscesses may result from aspiration of
      infectious material from the oropharyngeal cavity and the upper respiratory
      tract.
    explanation: >-
      Supports oropharyngeal aspiration as the initiating route into the lung.
  downstream:
  - target: Polymicrobial Anaerobic-Aerobic Lung Infection
    causal_link_type: DIRECT
    description: >-
      Aspirated oral and upper-airway material seeds the lower respiratory tract
      with mixed anaerobic and aerobic flora.
    evidence:
    - reference: PMID:20477271
      reference_title: "Aspiration pneumonia and primary lung abscess: diagnosis and therapy of an aerobic or an anaerobic infection?"
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      snippet: >-
        Pneumonia and primary lung abscesses may result from aspiration of
        infectious material from the oropharyngeal cavity and the upper respiratory
        tract.
      explanation: >-
        Directly connects aspiration of infectious upper-airway material to
        pneumonia and primary lung abscess.

- name: Polymicrobial Anaerobic-Aerobic Lung Infection
  role: trigger
  description: >-
    The infected lung or pleural space usually contains several anaerobic
    species, often with coexisting nonanaerobes, so anaerobic pneumonia is better
    modeled as a community infection than as a single-species pneumonia.
  biological_scale: TISSUE
  locations:
  - preferred_term: lung
    term:
      id: UBERON:0002048
      label: lung
  evidence:
  - reference: PMID:8324128
    reference_title: "Bacteriology of anaerobic pleuropulmonary infections: preliminary report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      cultures yielded an average of 3.0 anaerobes and 0.6 nonanaerobes per
      specimen.
    explanation: >-
      Quantifies the polymicrobial anaerobe-heavy composition of anaerobic
      pleuropulmonary infection specimens.
  - reference: PMID:12959026
    reference_title: "[Incidence of anaerobic bacteria in respiratory tract infections]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Lower respiratory infections are usually either polymicrobial or mixed
      anaerobic-aerobic infections.
    explanation: >-
      Describes the mixed anaerobic-aerobic bacteriology of lower respiratory
      anaerobic infections.
  downstream:
  - target: Prevotella-Enhanced Alveolar Adhesion
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      In model systems, Prevotella products increase lower-airway bacterial
      adhesion, suggesting one mechanism by which oral anaerobes can amplify
      coinfecting bacterial pneumonia.
  - target: Fever
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Mixed anaerobic-aerobic infection in the lung can produce systemic
      febrile illness.

- name: Prevotella-Enhanced Alveolar Adhesion
  role: amplifier
  description: >-
    Products from the oral anaerobe Prevotella intermedia can amplify
    pneumococcal adhesion to human alveolar epithelial cells together with
    platelet-activating-factor receptor expression. This is modeled as indirect
    support because the experiment used a pneumococcal coinfection rather than
    a purely anaerobic pneumonia.
  biological_scale: CELLULAR
  cell_types:
  - preferred_term: epithelial cell of lower respiratory tract
    term:
      id: CL:0002632
      label: epithelial cell of lower respiratory tract
  biological_processes:
  - preferred_term: adhesion of symbiont to host
    term:
      id: GO:0044406
      label: adhesion of symbiont to host
    modifier: INCREASED
  downstream:
  - target: Anaerobe-Amplified Pneumonic Inflammation
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Higher lower-airway bacterial adhesion can increase the lung bacterial
      burden that drives host cytokine release.
  evidence:
  - reference: PMID:24478074
    reference_title: Prevotella intermedia induces severe bacteremic pneumococcal pneumonia in mice with upregulated platelet-activating factor receptor expression.
    supports: SUPPORT
    evidence_source: IN_VITRO
    directness: INDIRECT
    snippet: >-
      In A549 cells, PiSup increased pneumococcal adhesion and PAFR transcript
      levels.
    explanation: >-
      Shows that Prevotella products increase pneumococcal adhesion to human
      alveolar epithelial cells and induce the host receptor implicated in that
      adhesion; the assay is indirect because it tests pneumococcal adhesion
      under Prevotella supernatant exposure.

- name: Anaerobe-Amplified Pneumonic Inflammation
  role: amplifier
  description: >-
    In mouse coinfection experiments, Prevotella intermedia products intensified
    pneumococcal pneumonia, bacterial burden, and alveolar cytokine production.
    This supports an anaerobe-mediated inflammatory amplification arm rather
    than a direct human anaerobic-pneumonia mechanism.
  biological_scale: TISSUE
  locations:
  - preferred_term: lung
    term:
      id: UBERON:0002048
      label: lung
  biological_processes:
  - preferred_term: inflammatory response
    term:
      id: GO:0006954
      label: inflammatory response
    modifier: INCREASED
  downstream:
  - target: Necrotizing Cavitary Lung Destruction
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Sustained mixed bacterial growth and cytokine-rich inflammation are
      upstream of the tissue destruction that distinguishes cavitary anaerobic
      disease from uncomplicated pneumonia.
  evidence:
  - reference: PMID:24478074
    reference_title: Prevotella intermedia induces severe bacteremic pneumococcal pneumonia in mice with upregulated platelet-activating factor receptor expression.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    directness: INDIRECT
    snippet: >-
      Mice inoculated with S. pneumoniae plus PiSup exhibited a significantly
      lower survival rate, higher bacterial loads in the lungs, spleen, and
      blood, and higher inflammatory cytokine levels in the bronchoalveolar
      lavage fluid (macrophage inflammatory protein 2 and tumor necrosis factor
      alpha) than those infected without PiSup.
    explanation: >-
      Demonstrates Prevotella-mediated inflammatory amplification in a
      pneumococcal pneumonia model, an indirect model for oral-anaerobe synergy
      in the lower airway.

- name: Necrotizing Cavitary Lung Destruction
  role: outcome
  description: >-
    Untreated or severe anaerobic infection can progress over days from
    aspiration pneumonia to necrotizing pneumonia and pulmonary abscess, with
    foul-smelling putrid sputum and cavitary disease as delayed manifestations.
  biological_scale: TISSUE
  locations:
  - preferred_term: lung
    term:
      id: UBERON:0002048
      label: lung
  biological_processes:
  - preferred_term: inflammatory response
    term:
      id: GO:0006954
      label: inflammatory response
    modifier: INCREASED
  evidence:
  - reference: PMID:20477271
    reference_title: "Aspiration pneumonia and primary lung abscess: diagnosis and therapy of an aerobic or an anaerobic infection?"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Necrotizing pneumonia, pulmonary abscesses and the characteristic,
      foul-smelling, putrid discharge only occur 8-14 days after the initial
      aspiration event.
    explanation: >-
      Links aspiration-associated cavitary anaerobic disease to necrotizing
      pneumonia, lung abscess, and the delayed putrid sputum manifestation.
  downstream:
  - target: Lung Abscess
    causal_link_type: DIRECT
    description: >-
      Necrotizing anaerobic pneumonia destroys lung parenchyma and forms
      cavitary pulmonary abscesses.
    evidence:
    - reference: PMID:20477271
      reference_title: "Aspiration pneumonia and primary lung abscess: diagnosis and therapy of an aerobic or an anaerobic infection?"
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      snippet: >-
        Necrotizing pneumonia, pulmonary abscesses and the characteristic,
        foul-smelling, putrid discharge only occur 8-14 days after the initial
        aspiration event.
      explanation: >-
        Places pulmonary abscess downstream of the initial aspiration event.
  - target: Productive Cough
    causal_link_type: DIRECT
    description: >-
      Cavitary anaerobic disease can drain foul, putrid material into the
      airway and cause productive cough.
    evidence:
    - reference: PMID:20477271
      reference_title: "Aspiration pneumonia and primary lung abscess: diagnosis and therapy of an aerobic or an anaerobic infection?"
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      snippet: >-
        Necrotizing pneumonia, pulmonary abscesses and the characteristic,
        foul-smelling, putrid discharge only occur 8-14 days after the initial
        aspiration event.
      explanation: >-
        Supports putrid sputum as a delayed manifestation of cavitary anaerobic
        pneumonia.
  - target: Pleural Extension of Infection
    causal_link_type: DIRECT
    description: >-
      Peripheral or ruptured cavitary infection can extend through the pleura,
      creating empyema or bronchopleural fistula.
  - target: Hemoptysis
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Cavitary lung abscess can erode inflamed airway and vascular tissue,
      producing hemoptysis in some anaerobic abscess presentations.
  - target: Chest pain
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Cavitary and pleural inflammation can manifest with chest pain.

- name: Pleural Extension of Infection
  role: outcome
  description: >-
    Cavitary lung infection can involve the pleural surface or rupture into the
    pleural space, producing empyema and, in severe cases, bronchopleural
    fistula that requires source control.
  biological_scale: TISSUE
  locations:
  - preferred_term: pleura
    term:
      id: UBERON:0000977
      label: pleura
  downstream:
  - target: Pleural Empyema
    causal_link_type: DIRECT
    description: >-
      Pleural extension seeds infected fluid in the pleural cavity and produces
      empyema.
    evidence:
    - reference: PMID:20477271
      reference_title: "Aspiration pneumonia and primary lung abscess: diagnosis and therapy of an aerobic or an anaerobic infection?"
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      snippet: >-
        Since antibiotics can provide cure in 80-90% of cases, surgical
        procedures are limited to severe complications, such as pleural empyema.
      explanation: >-
        Identifies pleural empyema as a severe complication of aspiration
        pneumonia and primary lung abscess.

phenotypes:
- name: Fever
  description: >-
    Systemic febrile illness accompanies lung abscess, one of the cavitary
    manifestations of anaerobic pneumonia.
  phenotype_term:
    preferred_term: Fever
    term:
      id: HP:0001945
      label: Fever
  evidence:
  - reference: PMID:41886424
    reference_title: "Clinical presentation and management outcomes of pediatric lung abscess: A retrospective cohort study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Systemic symptoms such as fever (91%) and hypoactivity (91%) were common.
    explanation: >-
      Reports fever in a pediatric lung-abscess cohort, grounding fever as a
      common systemic feature of cavitary pneumonia while not claiming that all
      pediatric abscesses were anaerobic.
- name: Productive Cough
  description: >-
    Cough with sputum is common in lung abscess, and the sputum may become
    foul-smelling and putrid as anaerobic necrotizing infection matures.
  phenotype_term:
    preferred_term: Productive cough
    term:
      id: HP:0031245
      label: Productive cough
  evidence:
  - reference: PMID:41886424
    reference_title: "Clinical presentation and management outcomes of pediatric lung abscess: A retrospective cohort study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Cough was reported in 87% of cases, with varying patterns (dry, wet, or
      both).
    explanation: >-
      Establishes cough as a frequent lung-abscess feature, with wet/productive
      cough represented among the reported patterns.
  - reference: PMID:20477271
    reference_title: "Aspiration pneumonia and primary lung abscess: diagnosis and therapy of an aerobic or an anaerobic infection?"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Necrotizing pneumonia, pulmonary abscesses and the characteristic,
      foul-smelling, putrid discharge only occur 8-14 days after the initial
      aspiration event.
    explanation: >-
      Supports the anaerobic-specific putrid sputum quality that can accompany
      productive cough after cavitation.
- name: Hemoptysis
  description: >-
    Some oral-anaerobe lung abscess presentations include hemoptysis together
    with cough, fever, and chest pain.
  phenotype_term:
    preferred_term: Hemoptysis
    term:
      id: HP:0002105
      label: Hemoptysis
  evidence:
  - reference: PMID:41054501
    reference_title: "Metagenomic Next-Generation Sequencing Reveals Tannerella forsythia in Lung Abscesses: A Retrospective Case Series Linking Smoking, Oral Health, and Diagnostic Challenges."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The primary clinical manifestations were nonspecific respiratory symptoms,
      including cough, fever, chest pain, and hemoptysis.
    explanation: >-
      Documents hemoptysis in a small mNGS-confirmed Tannerella forsythia lung
      abscess series.
- name: Chest pain
  description: >-
    Anaerobic lung abscess can present with chest pain among other nonspecific
    respiratory symptoms.
  phenotype_term:
    preferred_term: Chest pain
    term:
      id: HP:0100749
      label: Chest pain
  evidence:
  - reference: PMID:41054501
    reference_title: "Metagenomic Next-Generation Sequencing Reveals Tannerella forsythia in Lung Abscesses: A Retrospective Case Series Linking Smoking, Oral Health, and Diagnostic Challenges."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The primary clinical manifestations were nonspecific respiratory symptoms,
      including cough, fever, chest pain, and hemoptysis.
    explanation: >-
      Documents chest pain in a small mNGS-confirmed Tannerella forsythia lung
      abscess series.
- name: Lung Abscess
  description: >-
    Cavitary pulmonary abscess is a hallmark destructive complication of
    aspiration-related anaerobic pneumonia.
  phenotype_term:
    preferred_term: Lung abscess
    term:
      id: HP:0025044
      label: Lung abscess
  evidence:
  - reference: PMID:20477271
    reference_title: "Aspiration pneumonia and primary lung abscess: diagnosis and therapy of an aerobic or an anaerobic infection?"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Necrotizing pneumonia, pulmonary abscesses and the characteristic,
      foul-smelling, putrid discharge only occur 8-14 days after the initial
      aspiration event.
    explanation: >-
      Places pulmonary abscess in the time course of aspiration-associated
      anaerobic cavitary disease.
- name: Pleural Empyema
  description: >-
    Extension of anaerobic pleuropulmonary infection to the pleural space can
    form an empyema that requires drainage or surgery.
  phenotype_term:
    preferred_term: Pleural empyema
    term:
      id: HP:0011919
      label: Pleural empyema
  evidence:
  - reference: PMID:23398871
    reference_title: "How important are anaerobic bacteria in aspiration pneumonia: when should they be treated and what is optimal therapy."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      These bacteria are relatively common in selected types of lung infections
      including aspiration pneumonia, lung abscess, necrotizing pneumonia and
      emphyema.
    explanation: >-
      Names pleural empyema among the selected lung infections where anaerobes
      are relatively common; the abstract misspells empyema as "emphyema".

diagnosis:
- name: Bronchoalveolar Lavage Metagenomic Sequencing
  description: >-
    Comprehensive metagenomic next-generation sequencing of bronchoalveolar
    lavage fluid can detect anaerobic sequences that targeted panels and routine
    culture miss, but the result must be interpreted against aspiration risk and
    oral-disease context because oral anaerobes can also be colonizers.
  diagnosis_term:
    preferred_term: metagenomic next-generation sequencing of bronchoalveolar lavage fluid
    term:
      id: NCIT:C101293
      label: Next Generation Sequencing
  evidence:
  - reference: PMID:42445473
    reference_title: "Detection Blind Spots in Microbial Culture, tNGS, and mNGS: Anaerobic Bacterial Infections in the Lung-A Retrospective Analysis of Two Cases."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In both cases, tNGS was unable to detect anaerobic pathogens due to the
      limited scope of anaerobic bacterial targets in commercial panels. In
      contrast, comprehensive mNGS, when correctly interpreted in conjunction
      with clinical context, can detect anaerobic sequences.
    explanation: >-
      Supports comprehensive mNGS as a diagnostic route for anaerobic pneumonia
      when targeted sequencing and routine testing miss anaerobes.
- name: Chest CT for cavitary lung lesions
  description: >-
    Chest CT characterizes cavitary lesions, air-fluid levels, and necrotizing
    pneumonia or lung abscess patterns when anaerobic pneumonia has progressed
    to cavitation.
  diagnosis_term:
    preferred_term: chest computed tomography
  evidence:
  - reference: PMID:41688916
    reference_title: A rare case of lung abscess caused by Mycoplasma pneumoniae in an adult with chronic obstructive pulmonary disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Chest CT revealed a cavitary lesion with an air-fluid level in the right
      lower lobe.
    explanation: >-
      Shows the classic CT appearance of a lung abscess with an air-fluid
      level.
  - reference: PMID:42487366
    reference_title: "Diagnostic Value of Non-contrast Lung CT in Evaluating Pulmonary Cavitary Lesions in Children and Adolescents: With a Specific Focus in Perforated Hydatid Cyst, Necrotizing Pneumonia, and Lung Abscess."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Non-contrast CT is a valuable diagnostic tool for pediatric cavitary
      pulmonary lesions, particularly necrotizing pneumonia and hydatid cysts.
    explanation: >-
      Supports CT as a tool for evaluating pediatric cavitary pulmonary
      lesions, including necrotizing pneumonia and lung abscess in the study
      differential.
- name: Protected lower-airway anaerobic sampling
  description: >-
    Anaerobic culture requires lower-airway, abscess, or pleural samples that
    minimize contamination by ubiquitous oral anaerobes; sputum is not reliable
    for anaerobic culture.
  diagnosis_term:
    preferred_term: protected lower airway sampling
  evidence:
  - reference: PMID:11695090
    reference_title: "[Diagnosis and therapy of abscess forming pneumonia]."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Bacteriological sampling should be performed using protected specimen
      brushing (PSB) technique.
    explanation: >-
      Recommends protected specimen brushing for bacteriologic sampling in
      abscess-forming aspiration pneumonia.
  - reference: PMID:12959026
    reference_title: "[Incidence of anaerobic bacteria in respiratory tract infections]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Appropriatte specimens include: pus, purulent fluid, biopsy specimen of
      lung, transtracheal aspirates and bronchoalveolar lavage (BAL).
    explanation: >-
      Lists uncontaminated lower-airway or purulent samples appropriate for
      anaerobic respiratory infection diagnosis.

treatments:
- name: Clindamycin and beta-lactam/beta-lactamase-inhibitor therapy
  description: >-
    Antibiotic therapy must cover anaerobes and frequent aerobic copathogens;
    clindamycin, amoxicillin-clavulanate, and ampicillin-sulbactam are named
    anti-anaerobic options, while metronidazole monotherapy is insufficient for
    mixed anaerobic-aerobic infection.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: clindamycin
      term:
        id: CHEBI:3745
        label: clindamycin
    - preferred_term: amoxicillin
      term:
        id: CHEBI:2676
        label: amoxicillin
    - preferred_term: ampicillin
      term:
        id: CHEBI:28971
        label: ampicillin
  target_mechanisms:
  - target: Polymicrobial Anaerobic-Aerobic Lung Infection
    treatment_effect: INHIBITS
    description: >-
      Anti-anaerobic antibiotics treat the mixed anaerobic-aerobic bacterial
      burden in the lung or pleural space.
  evidence:
  - reference: PMID:23398871
    reference_title: "How important are anaerobic bacteria in aspiration pneumonia: when should they be treated and what is optimal therapy."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Preferred antibiotics for these infections based on clinical experience are
      clindamycin and any betalactam-betalactamase inhibitor.
    explanation: >-
      Names clindamycin and beta-lactam/beta-lactamase inhibitor therapy as
      experience-based preferred antibiotic options.
  - reference: PMID:12959026
    reference_title: "[Incidence of anaerobic bacteria in respiratory tract infections]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Treatment includes an antibiotics regimen with an agent active against
      anaerobic and aerobic bacteria (therapy with 2 or 3 antimicrobial drugs).
    explanation: >-
      Supports broad antibacterial coverage rather than anaerobe-only treatment
      for mixed lower-respiratory anaerobic infection.
- name: Moxifloxacin therapy for aspiration pneumonia and primary lung abscess
  description: >-
    Moxifloxacin is a newer fluoroquinolone with anaerobic activity that has
    shown clinical efficacy similar to clindamycin and aminopenicillin/
    beta-lactamase-inhibitor regimens in aspiration pneumonia and primary lung
    abscess.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: moxifloxacin
      term:
        id: CHEBI:63611
        label: moxifloxacin
  target_mechanisms:
  - target: Polymicrobial Anaerobic-Aerobic Lung Infection
    treatment_effect: INHIBITS
    description: >-
      Antibacterial therapy suppresses the mixed bacterial burden that drives
      anaerobe-dominant aspiration pneumonia and primary lung abscess.
  evidence:
  - reference: PMID:20477271
    reference_title: "Aspiration pneumonia and primary lung abscess: diagnosis and therapy of an aerobic or an anaerobic infection?"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Aminopenicillins/beta-lactamase inhibitors, newer fluoroquinolones with
      anaerobic activity (moxifloxacin) and clindamycin have demonstrated equal
      clinical efficacy in the treatment of aspiration pneumonia and primary
      lung abscess.
    explanation: >-
      Names moxifloxacin among regimens with demonstrated efficacy in aspiration
      pneumonia and primary lung abscess.
- name: Abscess and empyema drainage
  description: >-
    Percutaneous, tube, or thoracoscopic drainage provides source control for
    infected lung abscesses or empyema collections that are not controlled by
    pharmacotherapy alone.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Drainage
    term:
      id: NCIT:C50434
      label: Drainage
  target_mechanisms:
  - target: Necrotizing Cavitary Lung Destruction
    treatment_effect: INHIBITS
    description: >-
      Source-control procedures drain abscesses or infected pleural collections
      that do not resolve with pharmacotherapy alone.
  - target: Pleural Extension of Infection
    treatment_effect: INHIBITS
    description: >-
      Drainage removes loculated infected pleural fluid and reduces pleural
      inflammatory burden.
  evidence:
  - reference: PMID:20223322
    reference_title: Thoracoscopic treatment of pediatric lung abscesses.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Thoracoscopic abscess drainage is associated with minimal morbidity and
      may result in faster recovery and a shorter course of antibiotics.
    explanation: >-
      Supports thoracoscopic drainage as a source-control option for lung
      abscesses with empyema in a pediatric surgical series.
- name: Thoracotomy and decortication for refractory empyema
  description: >-
    Empyema that remains loculated or refractory after initial drainage can
    require thoracotomy and decortication.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: Surgical Procedure
    term:
      id: NCIT:C15329
      label: Surgical Procedure
  target_mechanisms:
  - target: Pleural Extension of Infection
    treatment_effect: INHIBITS
    description: >-
      Decortication surgically clears organized infected pleural material when
      tube drainage is insufficient.
  evidence:
  - reference: PMID:20477271
    reference_title: "Aspiration pneumonia and primary lung abscess: diagnosis and therapy of an aerobic or an anaerobic infection?"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Since antibiotics can provide cure in 80-90% of cases, surgical procedures
      are limited to severe complications, such as pleural empyema.
    explanation: >-
      Supports reserving surgery for severe complications after most cases are
      managed medically.
  - reference: PMID:22610800
    reference_title: Evolving experience in the management of empyema thoracis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Fourteen out of seventeen (82.35%) of the patients who were initially
      treated with thoracocentesis or tube thoracostomy eventually needed
      thoracotomy.
    explanation: >-
      Documents escalation from initial drainage to thoracotomy in a
      retrospective empyema thoracis surgical cohort.

notes: >-
  Anaerobic pneumonia is often investigated through the adjacent aspiration
  pneumonia and lung-abscess literatures rather than a cleanly separated
  epidemiologic entity. Culture-based series are biased by the requirement for
  lower-airway or pleural specimens that are not contaminated by oral flora, and
  modern studies increasingly report aerobic Gram-negative bacilli in aspiration
  pneumonia; this entry therefore models anaerobic pneumonia as the
  anaerobe-dominant end of the aspiration/lung-abscess spectrum rather than as a
  claim that every aspiration pneumonia is anaerobic. Several cached PMIDs from
  the OpenScientist run remain navigation-only: broad aspiration-pneumonia
  epidemiology, veterinary aspiration models, and incidental abscess case reports
  were left uncited when they did not directly support the human
  anaerobe-dominant mechanism.
review_notes: >-
  Deliberately lumped. The four anaerobes in this entry -- Prevotella,
  Fusobacterium nucleatum, Peptostreptococcus and Bacteroides -- are kept together
  as one undifferentiated stratum after a rung-3 review against the six
  differentiating axes of design decisions section 3e (issue dismech#10115 decision 2).
  The decisive fact is that they do not partition cases: lower respiratory
  anaerobic infection is polymicrobial, the cited bacteriology series recovered an
  average of three anaerobes per specimen with all four genera among the commonest
  isolates (PMID:8324128, PMID:12959026), and a single empiric regimen covering the
  whole group is what treats the disease, with aminopenicillin/beta-lactamase
  inhibitor, moxifloxacin and clindamycin reported as equally effective
  (PMID:20477271). A `has_subtypes` row is a clinical stratum, and a case yielding
  Prevotella and Fusobacterium and Peptostreptococcus together cannot be assigned
  to one. Searches run on 2026-10-03: PubMed `(Prevotella[tiab] AND
  Fusobacterium[tiab] AND (pneumonia[tiab] OR "lung abscess"[tiab])) AND
  (differ*[tiab] OR compar*[tiab] OR outcome*[tiab])` returned 19 records, all oral
  or airway microbiome studies rather than per-genus clinical comparisons;
  `"Fusobacterium nucleatum"[tiab] AND pneumonia[tiab] AND (prognos*[tiab] OR
  mortality[tiab] OR severity[tiab])` returned 5, none comparing genera within
  anaerobic pneumonia; `Peptostreptococcus[tiab] AND (pneumonia[tiab] OR "lung
  abscess"[tiab]) AND (treatment[tiab] OR susceptibilit*[tiab])` returned 32, with
  no genus-specific first-line recommendation; and `anaerobic[tiab] AND
  pneumonia[tiab] AND polymicrobial[tiab]` returned 42, confirming the mixed-flora
  picture rather than contradicting it.

  The strongest contrary evidence found, recorded here so that a reviewer can
  disagree on the record rather than having to rediscover it, is PMID:30951830, a
  susceptibility survey of exactly these organisms as causes of aspiration
  pneumonia. It reports that Fusobacterium spp. were susceptible to every drug
  tested except ampicillin and showed no beta-lactamase activity, that Bacteroides
  fragilis and Peptostreptococcus spp. showed decreased susceptibility to
  cefmetazole or flomoxef, and that Prevotella spp. showed decreased ceftriaxone
  susceptibility. Drug susceptibility is one of the six axes, so this is a real
  near miss. It is judged insufficient here for two reasons: the differences are
  microbiological rather than clinical, in that no source names a genus-specific
  first-line regimen for anaerobic pneumonia or a clinical entity the field
  diagnoses as, say, Prevotella pneumonia; and the co-isolation above means the
  susceptibility profile of a case is the union of whatever grew, which is the
  reason broad anaerobic cover is given empirically. The paper is cached and named
  here but is not cited as evidence, because it supports no claim this entry makes.
  Rule R10 applies: if a source documents a genus-specific regimen or a
  genus-attributable clinical course, the row should be added then.
📚

References & Deep Research

Deep Research

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Evaluations and curation notes (1)

Create: Anaerobic Pneumonia · 2026-09-26T03:01:55Z · View source

Created the Anaerobic Pneumonia entry from an OpenScientist deep-research report. Curated MONDO:0004649 as an anaerobe-dominant pneumonia overlapping aspiration pneumonia and lung abscess, with genus-level Prevotella, Fusobacterium nucleatum, Peptostreptococcus, and Bacteroides infectious agents; a four-node aspiration-to-polymicrobial-infection-to-inflammatory-adhesion-to-necrotizing-cavitary-destruction pathograph; fever, productive cough, lung abscess, and pleural empyema phenotypes; bronchoalveolar-lavage mNGS diagnosis; and anti-anaerobic pharmacotherapy plus drainage/surgery treatments. The OpenScientist report resolved 38/38 references but marked six report quotes unsupported and proposed several wrong HP/NCIT CURIEs plus one obsolete GO term, so ontology bindings were rechecked with OAK and unsupported or off-entity report claims were left out.

OpenScientist ▸
Anaerobic Pneumonia (MONDO:0004649): A Comprehensive Disease Characteristics Report
openscientist-autonomous 38 citations 2026-09-25T19:52:43.338690

Anaerobic Pneumonia (MONDO:0004649): A Comprehensive Disease Characteristics Report

Category: Infectious Disease | Evidence base: 51 papers reviewed, 10 confirmed findings

Summary

Anaerobic pneumonia is an acquired, non-genetic infectious lung disease caused by aspiration of oropharyngeal and gingival anaerobic bacteria into dependent lung segments. It is fundamentally a polymicrobial infection, dominated by obligate anaerobes—principally pigmented and nonpigmented Prevotella species, Fusobacterium nucleatum, Peptostreptococcus species, and Bacteroides species—that frequently co-exist with microaerophilic streptococci and aerobic Gram-negative bacilli. Because the causative organisms are members of the normal mouth flora, the disease has no Mendelian genetic basis; instead its "etiology" is a chain that begins with a breach of airway protective reflexes (impaired consciousness, dysphagia, impaired cough) combined with a large oral bacterial inoculum (periodontal disease), which permits aspirated anaerobes to establish a synergistic, tissue-destructive infection in the lung.

The disease follows a characteristic subacute course: over roughly 8–14 days after the aspiration event, an initial aspiration pneumonitis evolves into necrotizing pneumonia, then to cavitary lung abscess, and can progress to empyema and bronchopleural fistula. The clinical hallmark is foul-smelling, putrid sputum with fever and productive cough, and the diagnostic hallmark is a cavitary lesion with an air–fluid level in a dependent lung segment on chest imaging. Anaerobic culture is often falsely negative because specimens are contaminated by upper-airway flora, and modern comprehensive metagenomic next-generation sequencing (mNGS) of bronchoalveolar lavage fluid can recover fastidious anaerobes missed by culture and targeted panels.

Antibiotic therapy cures 80–90% of cases, with clindamycin and β-lactam/β-lactamase-inhibitor combinations as first-line agents; surgery/drainage is reserved for complications such as empyema. Prevention rests on oral hygiene (professional oral care in long-term-care settings) and dysphagia management. A notable epidemiologic trend is a shift in microbial etiology away from classical anaerobes toward Gram-negative bacilli (e.g., Klebsiella pneumoniae), and mortality in severe aspiration-related disease remains high (20–50% in critically ill patients). The disease occurs naturally across mammalian species, with dogs (post-anesthetic aspiration, laryngeal paralysis, megaesophagus) and horses (transport-associated pleuropneumonia) serving as informative veterinary counterparts.

Section 1. Disease Information

Overview. Anaerobic pneumonia is a lower-respiratory-tract infection of the lung parenchyma caused predominantly by obligate anaerobic bacteria that normally colonize the oral cavity, gingival crevice, and upper airway. It is most often the consequence of aspiration of oropharyngeal secretions, and it sits on a clinical-pathological continuum with aspiration pneumonitis, necrotizing pneumonia, lung abscess, and empyema. Anaerobes "are involved in infections such as pneumonia, aspiration pneumonia, lung abscess and empyema" and "lower respiratory infections are usually either polymicrobial or mixed anaerobic-aerobic infections" (PMID: 12959026).

Key identifiers. - MONDO: 0004649 - MeSH: "Pneumonia, Aspiration" / anaerobic bacterial infections (closest indexing terms; there is no dedicated OMIM entry). - ICD-10: J69.0 (Pneumonitis due to inhalation of food and vomit / aspiration pneumonia) is the code used in mortality databases for the aspiration process (PMID: 42740601); anaerobic bacterial pneumonia maps to J15.8/J15.9 (other/unspecified bacterial pneumonia). - OMIM / Orphanet: Not applicable — this is an acquired infectious disease, not a Mendelian or rare genetic disorder.

Synonyms / alternative names. Anaerobic pleuropulmonary infection; anaerobic lung infection; aspiration pneumonia (overlapping term); putrid/necrotizing pneumonia; anaerobic lung abscess (when cavitary).

Source of information. The knowledge here is derived from aggregated disease-level clinical and microbiological literature — bacteriologic case series, cohort studies, systematic reviews, and mechanistic/animal studies — rather than from individual patient EHR records.

Section 2. Etiology

Primary cause — infectious/mechanistic, not genetic. The proximate cause is aspiration of oropharyngeal/gingival flora into the lower respiratory tract in a host with impaired airway protection. There is no causal gene, no Mendelian inheritance, and no defined pathogenic variant for anaerobic pneumonia itself (see Section 4). The dominant organisms are obligate anaerobes; a retrospective bacteriologic study of 116 specimens from 110 patients found that "cultures yielded an average of 3.0 anaerobes and 0.6 nonanaerobes per specimen. The most commonly encountered anaerobes were pigmented Prevotella species, nonpigmented Prevotella species, Fusobacterium nucleatum, Peptostreptococcus species, and Bacteroides species" (PMID: 8324128). In acute community-acquired lung abscess, a mean of 2.3 bacterial species per patient was isolated, with "anaerobes alone being isolated in 44% of cases, aerobes alone in 19%, and mixed aerobic and anaerobic isolates in 22%" (PMID: 7555164).

Environmental / clinical risk factors. The classic predisposing conditions reduce or defeat airway protective reflexes: - Compromised mental status — "alcoholism, sedatives, stroke" — and esophageal dysfunction — "herniation, vomiting" — are important risk factors (PMID: 11695090). - Swallowing dysfunction, impaired cough reflex, and degenerative neurological diseases predispose to aspiration pneumonia (PMID: 39536943). - Oral frailty / dysphagia markers carry measurable risk: in long-term-care residents, "inability to gargle (OR = 1.991; 95% CI: 1.139–3.479) and unclear speech (OR = 1.752; 95% CI: 1.085–2.829) remained significantly associated with" aspiration pneumonia (PMID: 42548261). - Periodontal disease / large oral bacterial inoculum supplies the pathogens; anaerobes "are predominant components of normal oral cavity, upper respiratory tract" flora (PMID: 12959026). - Diabetes mellitus is a risk factor for the Gram-negative (Klebsiella) subset of lung abscess: "Lung abscess due to K. pneumoniae was associated with underlying diabetes mellitus (odds ratio [OR], 4.3; 95% confidence interval [CI], 1.0–18.4; P = .039)" (PMID: 15824979). - Age / functional dependence — older, functionally dependent inpatients are heavily affected; ~20% of dementia-care-eligible hospitalizations were for pneumonia or aspiration pneumonia (PMID: 42711657).

Genetic risk factors. None established in humans. (In dogs, a heritable predisposition to megaesophagus indirectly raises aspiration risk — see Section 14.)

Protective factors. Environmental/behavioral: professional oral health care and dysphagia rehabilitation reduce risk (Sections 5, 13). No genetic protective variants are defined.

Gene–environment interactions. Not applicable in humans; the disease is driven by host functional state (consciousness, swallowing) interacting with oral microbial burden rather than by host genotype.

Section 3. Phenotypes

The clinical phenotype is a subacute febrile pneumonia with productive, putrid sputum, often progressing to cavitary disease. Phenotype frequencies (largely from lung-abscess cohorts) and suggested HPO terms:

Phenotype (type) Frequency / characteristics Suggested HPO term
Fever (symptom/sign) 91% in a pediatric lung-abscess cohort (n=23); subacute onset HP:0001945 (Fever)
Productive cough (symptom) 87% ("Cough was reported in 87% of cases") HP:0031245 (Productive cough) / HP:0012735 (Cough)
Hypoactivity / malaise (sign) 91% HP:0025406 (Fatigue-related); constitutional
Foul-smelling / putrid sputum (sign) Characteristic; appears 8–14 days post-aspiration HP:0031246 (Purulent sputum); putrid odor is disease-specific
Cavitary pulmonary lesion (radiographic/physical manifestation) Hallmark; air–fluid level on CT HP:0025426 (Pulmonary cavity)
Pleural effusion / empyema (sign) Complication; loculated fluid HP:0002202 (Pleural effusion); HP:0032247 (Empyema)
Hemoptysis, chest pain (symptoms) Reported in abscess series HP:0002105 (Hemoptysis); HP:0100749 (Chest pain)

Symptom characteristics. Onset is typically adult (and geriatric), though pediatric cases occur; the pattern is subacute/insidious. Classic anaerobic infection produces "the characteristic, foul-smelling, putrid discharge [that] only occur[s] 8–14 days after the initial aspiration event," together with "necrotizing pneumonia [and] pulmonary abscesses" (PMID: 20477271). In pediatric lung abscess, "systemic symptoms such as fever (91%) and hypoactivity (91%) were common. Cough was reported in 87% of cases" (PMID: 41886424). Severity ranges from mild pneumonitis to severe necrotizing/cavitary disease; progression without treatment is progressive, but with antibiotics is usually resolving (radiologic resolution in 91% after ~4.8 weeks of antibiotics in the pediatric cohort).

Quality-of-life impact. Not formally quantified with EQ-5D/SF-36 in the reviewed literature. Indirect impact is substantial: aspiration pneumonia drives prolonged hospitalization, ICU admission, nasogastric-tube dependence, and functional decline in frail and dementia populations (PMID: 42472523; PMID: 42711657).

Section 4. Genetic / Molecular Information

Not applicable — this is an acquired bacterial infection. There are no causal human genes, no pathogenic germline or somatic variants (no ClinVar/HGMD entries), no modifier genes, no disease-defining epigenetic marks, and no chromosomal abnormalities associated with anaerobic pneumonia. Host susceptibility is determined by functional states (level of consciousness, swallowing and cough reflexes, oral hygiene, comorbidities such as diabetes) rather than by genotype.

The only genetic finding in the broader disease space concerns an animal model of a predisposing condition: canine congenital idiopathic megaesophagus (which causes recurrent aspiration pneumonia) is associated with an intronic VNTR in MCHR2 (Melanin-Concentrating Hormone Receptor 2) in German Shepherd dogs, with "The single-copy allele … strongly associated with CIM (P-val = 1.32×10⁻¹⁷)" (PMID: 35271580). This is a susceptibility locus for aspiration risk in dogs, not for anaerobic pneumonia per se, and has no human ortholog association with the disease.

Section 5. Environmental Information

Environmental / occupational factors. None of the classical toxicologic type (no CTD toxin associations). The relevant "exposure" is the microbial reservoir of the oral cavity plus events that provoke aspiration (sedation, anesthesia, alcohol intoxication, vomiting).

Lifestyle factors. Alcoholism (compromised consciousness), sedative use, and smoking are contributors. Long-term smoking was common (75%) in an mNGS-confirmed anaerobic lung-abscess series, in which "all patients had oral diseases, and 75% were long-term smokers" (PMID: 41054501). Poor oral hygiene/periodontal disease is a modifiable lifestyle-linked exposure.

Infectious agents (NCBI Taxonomy). The pathogens are the etiologic core of the disease: - Prevotella spp. (e.g., Prevotella intermedia) — pigmented and nonpigmented (NCBI:txid838 genus) - Fusobacterium nucleatum (NCBI:txid851) - Peptostreptococcus spp. (NCBI:txid1257) - Bacteroides spp. (NCBI:txid816) - Microaerophilic/anaerobic streptococci (co-pathogens) - Actinomyces spp. (e.g., A. graevenitzii) in actinomycosis-type presentations (PMID: 40923736) - Increasingly, aerobic Gram-negative bacilli — Klebsiella pneumoniae (NCBI:txid573) — in the shifting etiology (PMID: 15824979)

"Peptostreptococcus, Fusobacterium, Prevotella and Bacteroides are the most common anaerobes" in lower respiratory infections (PMID: 12959026).

Section 6. Mechanism / Pathophysiology

Ordered causal chain (initiating lesion → clinical manifestation)

  1. Impaired airway protection (depressed consciousness, dysphagia, impaired cough reflex; alcohol, sedation, stroke, megaesophagus) leads to loss of the normal barrier that clears oropharyngeal secretions.
  2. This results in aspiration of oropharyngeal/gingival secretions carrying a high anaerobic bacterial load into the lower respiratory tract — "the process of alveolar inflammation induced by the inhalation of oropharyngeal secretions into the lower respiratory tract" (PMID: 39536943).
  3. Aspirated material deposits by gravity in dependent lung segments (posterior segments of upper lobes, superior segments of lower lobes), determining lesion location; pulmonary distribution is "determined by a complex interplay between infection routes, lung anatomy and physiology, host defense mechanisms" (PMID: 42279473).
  4. Anaerobes establish a polymicrobial/mixed anaerobic-aerobic community in the airway (PMID: 12959026).
  5. Microbial synergy amplifies infection and inflammation — inferred from model evidence: supernatant of the periodontopathic anaerobe Prevotella intermedia upregulated alveolar platelet-activating-factor receptor (PAFR) and "in A549 cells, PiSup increased pneumococcal adhesion and PAFR transcript levels," producing more severe bacteremic pneumonia with higher MIP-2 and TNF-α in mice (PMID: 24478074).
  6. Sustained mixed infection with anaerobic tissue-destroying enzymes and host neutrophilic inflammation leads to tissue necrosis → necrotizing pneumonia (branch point).
  7. Necrosis results in liquefaction and cavitation → lung abscess with an air–fluid level; putrid sputum reflects anaerobic metabolic byproducts; these features "only occur 8–14 days after the initial aspiration event" (PMID: 20477271).
  8. Branch: extension to the pleural space results in parapneumonic effusion → empyema; erosion into airways results in bronchopleural fistula and metastatic (e.g., subpleural, brain) abscess (PMID: 41174571).

Detail by category

  • Molecular pathways. PAFR-mediated bacterial adhesion (model evidence) links anaerobe products to enhanced pathogen attachment and cytokine induction (MIP-2/CXCL2, TNF-α) (PMID: 24478074). Suggested GO terms: GO:0006954 (inflammatory response), GO:0071222 (cellular response to lipopolysaccharide).
  • Cellular processes. Neutrophilic inflammation, phagocytosis, tissue necrosis. GO:0006909 (phagocytosis), GO:0070265 (necrotic cell death), GO:0002438 (acute inflammatory response to antigenic stimulus).
  • Immune involvement. Innate neutrophil-dominated response; no autoimmunity or primary immunodeficiency required, though immunosuppression worsens outcome. GO:0006955 (immune response).
  • Tissue-damage mechanisms. Necrosis and abscess formation via bacterial proteases/toxins and host proteolytic burst; suppurative and, in Actinomyces, granulomatous inflammation with sulfur granules (PMID: 40923736).
  • Molecular profiling. No transcriptomic/proteomic/metabolomic host disease signatures are established for anaerobic pneumonia; the most relevant "omics" tool is metagenomic sequencing for pathogen detection (Section 10), not host profiling.

Cell types involved (CL): CL:0000775 (neutrophil), CL:0000235 (macrophage), CL:0000066 (epithelial cell — alveolar/airway), CL:0002063 (type II pneumocyte; A549 is a type-II-like line).

Section 7. Anatomical Structures Affected

  • Primary organ: lung (UBERON:0002048), respiratory system (UBERON:0001004).
  • Localization: dependent lung segments — posterior segments of upper lobes and superior segments of lower lobes — reflecting gravitational deposition of aspirate. Right lower lobe is frequently involved (right main bronchus is more vertical); cases document right-lower-lobe abscess (PMID: 41688916).
  • Lateralization: commonly unilateral and dependent-segment predominant, but may be bilateral.
  • Secondary/adjacent structures: pleura and pleural cavity (UBERON:0002402 / UBERON:0002384) → empyema; bronchi (UBERON:0002185) → bronchopleural fistula; mediastinum by extension.
  • Tissue level: alveolar and bronchial epithelium (UBERON:0000483), lung parenchyma/connective tissue; suppurative destruction of parenchyma.
  • Subcellular (GO cellular component): infection is extracellular/luminal; host responses engage plasma-membrane receptors (PAFR, GO:0005886 plasma membrane) and secretory/inflammatory machinery. No defined organelle-level lesion.
  • Body systems: respiratory (primary); systemic (sepsis/bacteremia) as complication.

Section 8. Temporal Development

  • Onset: predominantly adult and geriatric, though pediatric cases occur; pattern is subacute/insidious. The disease characteristically declares itself over 8–14 days after aspiration, when "necrotizing pneumonia, pulmonary abscesses and the characteristic, foul-smelling, putrid discharge" appear (PMID: 20477271).
  • Stages / progression: aspiration pneumonitis → necrotizing pneumonia → lung abscess → empyema/bronchopleural fistula. These "bacteria are relatively common in selected types of lung infections including aspiration pneumonia, lung abscess, necrotizing pneumonia and emphyema [empyema]" (PMID: 23398871).
  • Progression rate: subacute; slower than typical pyogenic (e.g., pneumococcal) pneumonia, contributing to delayed diagnosis.
  • Course pattern: typically progressive if untreated; can be recurrent when the predisposing condition (e.g., megaesophagus, persistent dysphagia) is uncorrected.
  • Duration: treatment courses are prolonged — weeks. Pediatric abscess achieved full radiologic resolution in 91% after ~4.8 weeks of antibiotics (PMID: 41886424).
  • Remission: treatment-induced remission is the norm with adequate antibiotics ± drainage.
  • Critical period for intervention: the window before cavitation/empyema — early antibiotic therapy and airway protection prevent progression.

Section 9. Inheritance and Population

  • Inheritance: none — acquired infectious disease; no Mendelian pattern, penetrance, expressivity, anticipation, mosaicism, founder effect, consanguinity, or carrier frequency applies to humans.
  • Epidemiology: anaerobic pneumonia is a subset of aspiration-related pneumonia; exact population prevalence/incidence for the anaerobic subset is not well delineated because of culture blind spots. Aspiration pneumonia is a major burden in elderly, institutionalized, and neurologically impaired populations (~20% of dementia-care hospitalizations involved pneumonia/aspiration pneumonia; PMID: 42711657).
  • Mortality: high in severe disease — "Aspiration pneumonia is a common and life-threatening condition among critically ill patients, with mortality reaching 20-50%," and a MIMIC-IV ICU cohort of 2,132 patients had 25.5% in-hospital mortality (PMID: 42721055). US aspiration-pneumonitis mortality with co-listed stroke declined from an age-adjusted 9.20 to 3.55 per 100,000 (1999–2024) (PMID: 42740601).
  • Demographics: male predominance in aspiration-pneumonitis mortality (AAMR 13.38→4.92 in men vs 6.79→2.46 in women); higher rates in nonmetropolitan/rural counties and the US South (PMID: 42740601).
  • Geographic microbiological variation: in Taiwan, ~21% of community-acquired lung abscesses were due to Klebsiella pneumoniae, reflecting regional dominance of Gram-negative etiology (PMID: 15824979).

Section 10. Diagnostics

The central diagnostic challenge is recovering the causative anaerobes. Routine culture frequently fails because specimens are contaminated by upper-airway flora and anaerobic bacteriology is technically demanding — anaerobes "are rarely recovered" and "anaerobic bacteriology is inadequate" (PMID: 23398871).

Imaging (RadLex/Radiopaedia). Chest radiograph and CT are the primary tools. The hallmark is a cavitary lesion with an air–fluid level in a dependent segment: "Chest CT revealed a cavitary lesion with an air-fluid level in the right lower lobe" (PMID: 41688916). Non-contrast high-resolution CT distinguishes necrotizing pneumonia, abscess, and other cavitary lesions using features such as irregular borders and pleural-effusion heterogeneity (PMID: 42487366). Radiographic pattern (lobar, bronchopneumonic, necrotizing, abscess-forming, cavitating) correlates with pathogen and host (PMID: 42279473).

Microbiological sampling. Uncontaminated specimens are needed: pus/purulent fluid, transtracheal aspirate, protected specimen brush, bronchoalveolar lavage (BAL), or pleural fluid (PMID: 12959026). Fiberoptic bronchoscopy with protected-specimen brushing also helps exclude airway obstruction/neoplasm.

Molecular / omics diagnostics. Metagenomic next-generation sequencing (mNGS) of BAL fluid overcomes culture and targeted-panel blind spots: "tNGS was unable to detect anaerobic pathogens due to the limited scope of anaerobic bacterial targets in commercial panels. In contrast, comprehensive mNGS, when correctly interpreted in conjunction with clinical context, can detect anaerobic sequences" (PMID: 42445473). mNGS has revealed fastidious anaerobes in culture-negative pediatric and adult abscesses (PMID: 39239243; PMID: 41054501).

Differential diagnosis of cavitary lung disease. "Differential diagnosis includes bronchial neoplasms, either as necrotizing carcinoma or as the cause of poststenotic cavernous pneumonia, other infectious diseases like tuberculosis, Pneumocystis carinii pneumonia or endocarditis with septic metastases, and lung artery embolism or vasculitis" (PMID: 11695090). Additional mimics in the reviewed literature: primary pulmonary osteosarcoma (PMID: 1430451), tuberculosis with niveau-like shadows (PMID: 8683908), infected pancreatic pseudocyst (PMID: 17352178), hydatid cyst, and pulmonary aspergilloma.

Genetic testing / screening: not applicable.

Section 11. Outcome / Prognosis

  • Cure / response: favorable with adequate therapy — antibiotics "can provide cure in 80-90% of cases" (PMID: 20477271); pediatric abscess resolved radiologically in 91% (PMID: 41886424).
  • Mortality: high in severe/critically ill and elderly frail patients (20–50%; ICU in-hospital 25.5%) (PMID: 42721055); persistent critical illness is common after aspiration-related respiratory failure and confers ~3-fold higher one-year mortality after onset (PMID: 42748124).
  • Complications: lung abscess, necrotizing pneumonia, empyema, bronchopleural fistula, subpleural/brain abscess (metastatic); severe necrotizing infection can evolve to "necrotizing pneumonia, multiple lung abscesses, bronchopleural fistula, empyema and subpleural abscess" (PMID: 41174571).
  • Prognostic factors: severity/critical illness, host frailty and comorbidity (diabetes, dementia, neurologic disease), Gram-negative etiology, empyema/loculation, and delayed diagnosis. Systemic inflammatory indices are being explored as ICU prognostic markers (PMID: 42721055).
  • Recovery: high with timely antibiotics ± drainage; recurrence occurs if the underlying aspiration risk is uncorrected.

Section 12. Treatment

Pharmacotherapy (first-line). "Preferred antibiotics for these infections based on clinical experience are clindamycin and any beta-lactam–beta-lactamase inhibitor" (PMID: 23398871). Equal clinical efficacy is reported for aminopenicillin/β-lactamase-inhibitor combinations, newer anti-anaerobic fluoroquinolones (moxifloxacin), and clindamycin (PMID: 20477271). Anaerobes are susceptible to "metronidazole … amoxicillin/clavulanate, ampicillin/sulbactam, piperacillin/tazobactam, imipenem and clindamycin" (PMID: 12959026).

β-lactamase coverage matters: "Thirty percent of the anaerobic gram-negative rods were beta-lactamase producers," justifying β-lactamase-inhibitor combinations (PMID: 8324128).

Metronidazole caveat: monotherapy fails because it lacks activity against the microaerophilic/aerobic streptococci in the mixed flora — combination therapy with an agent active against both anaerobes and aerobes is recommended (PMID: 12959026).

Drug / class Role NCIT (suggested)
Clindamycin (lincosamide) First-line NCIT:C376
Amoxicillin-clavulanate First-line β-lactam/BLI NCIT:C29257 (amoxicillin)
Ampicillin-sulbactam First-line β-lactam/BLI NCIT:C47384 (sulbactam)
Piperacillin-tazobactam Broad, incl. Gram-negatives NCIT:C61785
Moxifloxacin Anti-anaerobic fluoroquinolone NCIT:C1741
Metronidazole Adjunct only (not monotherapy) NCIT:C639
Imipenem/carbapenems Severe/mixed/GNB NCIT:C1602

Surgical / interventional. Reserved for complications: "Since antibiotics can provide cure in 80-90% of cases, surgical procedures are limited to severe complications, such as pleural empyema" (PMID: 20477271). For empyema, "the presence of loculated pleural fluid determined the need for thoracotomy" and decortication (PMID: 22610800). Minimally invasive percutaneous/thoracoscopic drainage is effective for abscess plus parapneumonic empyema, with faster recovery and shorter antibiotic courses (PMID: 20223322).

Supportive/rehabilitative. Airway protection, swallowing rehabilitation, nutrition, and treatment of the underlying predisposing condition.

Pharmacogenomics / advanced (gene, cell, RNA, targeted, immuno) therapies: not applicable.

Section 13. Prevention

Primary prevention — oral hygiene. Professional oral health care reduces respiratory infection in institutionalized populations: a systematic review of 13 studies (10 RCTs) found "moderate-to-strong evidence that onsite POHC in LTC homes, provided mostly by dental hygienists, is effective in preventing" mouth–lung infection (PMID: 38020079). Mechanistic rationale: "NHAP is associated with poor oral hygiene and may be caused by aspiration of oropharyngeal flora into the lung. Oral care measures to remove or disrupt oral plaque might reduce the risk of NHAP" (PMID: 30264525). A Cochrane review found low-quality evidence that professional oral care may reduce pneumonia-associated mortality (RR 0.41, 95% CI 0.24–0.72) though effects on incidence were inconclusive (PMID: 30264525).

Dysphagia management / secondary prevention. Comprehensive oral care improved swallowing function and enabled nasogastric-tube removal in dysphagic LTC residents in a multicenter RCT (PMID: 42472523). Early dysphagia screening and specialist swallow assessment reduce stroke-associated pneumonia risk (PMID: 42500843).

Behavioral / positioning. Meal positioning, aspiration precautions, avoiding oversedation, and careful peri-anesthetic airway management (analogous canine data show ~10-fold pneumonia reduction after protocol changes, PMID: 30375098).

Tertiary prevention. Prompt antibiotics and drainage to prevent progression to empyema/fistula.

Immunization / genetic screening / chemoprophylaxis: not applicable (no vaccine targets the polymicrobial oral flora).

Suggested NCIT: NCIT:C15311 (Preventive Intervention); NCIT:C15234 (Oral Hygiene).

Section 14. Other Species / Natural Disease

Aspiration/anaerobic pneumonia occurs naturally across mammals, providing veterinary counterparts and models:

Species (NCBI Taxon) Setting / finding Evidence
Dog — Canis lupus familiaris (txid9615) Post-anesthetic aspiration pneumonia in 0.17% of 140,711 cases; risk factors "regurgitation and administration of hydromorphone at induction" PMID: 24588929
Dog Aspiration pneumonia in 18.6–31.8% after arytenoid lateralization for laryngeal paralysis; "Postoperative megaesophagus (hazard ratio [HR], 2.58; 95% CI 1.56 to 3.93)" PMID: 26720085
Dog (German Shepherd) Congenital idiopathic megaesophagus → recurrent aspiration pneumonia; sex-differentiated, MCHR2 VNTR (GWAS P=1.32×10⁻¹⁷) PMID: 35271580
Dog Generalized megaesophagus: radiographic aspiration pneumonia predicts death before discharge; median survival 90 days PMID: 21671818
Horse — Equus caballus (txid9796) Transport-associated pleuropneumonia; "The finding of anaerobic bacteria in thoracic fluid was not associated with a lower survival rate"; 83% positive cultures PMID: 7744650

Comparative pathology. The core mechanism — aspiration of oral flora due to impaired airway protection or esophageal dysmotility, followed by mixed/anaerobic lung infection — is conserved across dogs, horses, and humans. Zoonotic potential: none (organisms are host-associated oral commensals; disease is not transmissible). Orthologous predisposition gene: MCHR2 (dog) has a human ortholog (HGNC MCHR2), but no human disease association is established.

Section 15. Model Organisms

  • Mouse (Mus musculus) — mechanistic model. The best experimental evidence for anaerobe-driven synergy comes from a mouse pneumococcal-pneumonia model in which Prevotella intermedia supernatant upregulated PAFR, increased pneumococcal adhesion, and produced "severe bacteremic pneumococcal pneumonia … with upregulated platelet-activating factor receptor expression," alongside higher MIP-2 and TNF-α (PMID: 24478074). Companion in vitro model: A549 human alveolar epithelial cells ("In A549 cells, PiSup increased pneumococcal adhesion and PAFR transcript levels").
  • Naturally occurring animal models (induced/spontaneous). Canine post-anesthetic aspiration, laryngeal-paralysis, and megaesophagus models (Section 14) recapitulate the predisposition-to-aspiration arm of the disease well, including risk-factor identification and outcome prediction. Equine transport pleuropneumonia models the anaerobic pleural-infection arm.
  • Phenotype recapitulation. Animal models reproduce aspiration risk, mixed/anaerobic lung infection, and complication (pleural) biology; the Prevotella mouse model reproduces anaerobe-driven inflammatory amplification.
  • Limitations. No single genetic model reproduces the full human polymicrobial anaerobic pneumonia; mouse work is largely mechanistic (synergy) rather than a faithful spontaneous-disease model; anaerobic culture/detection limitations apply in animals too.
  • Resources: MGI (mouse), OMIA (canine/equine natural disease), Cellosaurus (A549).

Mechanistic Model / Interpretation

  Impaired airway protection            High oral anaerobic load
  (↓consciousness, dysphagia,           (periodontal disease,
   ↓cough reflex; alcohol,               poor oral hygiene,
   sedation, stroke, mega-               smoking)
   esophagus)
│                                       │
└──────────────┬────────────────────────┘
       ▼
  ASPIRATION of oropharyngeal / gingival secretions
       │  (gravity → dependent lung segments;
       ▼   R-lower & posterior-upper lobes)
Polymicrobial / mixed anaerobic–aerobic community
(Prevotella, Fusobacterium, Peptostreptococcus,
 Bacteroides ± streptococci ± Gram-neg bacilli)
       │
       │  microbial SYNERGY
       │  (Prevotella → ↑PAFR → ↑adhesion,
       ▼   ↑MIP-2/TNF-α — model evidence)
Neutrophilic inflammation + tissue proteolysis
       │  (8–14 days)
       ▼
     NECROTIZING PNEUMONIA
       │
       ▼
LUNG ABSCESS (cavity + air–fluid level, putrid sputum)
  ┌────┴─────┐
  ▼          ▼
EMPYEMA          BRONCHOPLEURAL FISTULA / metastatic abscess
     (loculated →           (severe necrotizing disease)
      thoracotomy/
      decortication)

  Treatment: clindamycin OR β-lactam/β-lactamase-inhibitor
  (± metronidazole as adjunct, never alone) → cure 80–90%;
  drainage/surgery for empyema.
  Prevention: oral hygiene + dysphagia management (upstream nodes).

Upstream vs downstream. The two upstream nodes (impaired airway protection and high oral bacterial load) are the intervention targets — prevention acts here. Aspiration and polymicrobial synergy are the mechanistic core; necrosis, cavitation, and empyema are downstream, treated by antibiotics and drainage. A key modern modifier is the etiologic shift toward Gram-negative bacilli, which changes empiric-therapy considerations: "Accumulating evidence projects a fading contribution of anaerobic bacteria in aspiration pneumonia at the expense of Gram-negative bacilli" (PMID: 39536943).

Evidence Base

PMID Finding supported Contribution
8324128 F001, F003 Polymicrobial anaerobic bacteriology (3.0 anaerobes/specimen); 30% β-lactamase producers
7555164 F001 Frequency of anaerobic (44%) vs mixed etiology in lung abscess
11695090 F002, F006, F010 Risk factors; subacute course; cavitary differential diagnosis
20477271 F002, F003, F006, F009 8–14 day putrid course; 80–90% cure; surgery for empyema
42548261 F002 Oral-frailty risk ORs (gargle, speech)
23398871 F003, F009, F010 First-line antibiotics; complication spectrum; culture blind spots
12959026 F003, F007 Anaerobe genera, susceptibilities, combination-therapy rationale
39536943 F004, F007 Etiologic shift to Gram-negatives; definition of aspiration process
15824979 F004 Klebsiella lung abscess; diabetes association (OR 4.3)
42721055 F004, F011 ICU mortality 20–50% / 25.5%; inflammatory prognostic index
42740601 F004 US mortality trends and disparities
38020079 F005 Professional oral care prevents mouth–lung infection
30264525 F005 Cochrane: oral care pathogenesis/prevention rationale
41886424 F006 Symptom frequencies; radiologic resolution
41688916 F006 Hallmark cavitary air–fluid-level imaging
42279473 F006 Pulmonary distribution determinants
24478074 F007 Prevotella-driven synergy (PAFR, adhesion, cytokines) — model evidence
24588929 F008 Canine post-anesthetic aspiration risk factors
7744650 F008 Equine anaerobic pleuropneumonia
26720085 F008 Megaesophagus → aspiration (HR 2.58)
35271580 F008 Canine megaesophagus MCHR2 genetics (predisposition)
41174571 F009 Severe complication cascade (abscess→fistula→empyema)
22610800 F009 Empyema management (loculation → thoracotomy)
20223322 F009 Thoracoscopic drainage of abscess + empyema
42445473 F010 mNGS > culture/tNGS for anaerobes
39239243, 41054501 F010 mNGS detects fastidious anaerobes; smoking/oral disease context

Limitations and Knowledge Gaps

  1. Diagnostic underascertainment. The anaerobic subset of aspiration pneumonia is systematically underdiagnosed because anaerobes are hard to culture and specimens are contaminated by oral flora (PMID: 23398871). Reported bacteriology therefore likely underestimates true anaerobic contribution, while the observed "shift to Gram-negatives" may partly reflect detection-method changes rather than true epidemiologic change.
  2. No dedicated epidemiology. Prevalence/incidence figures are for aspiration pneumonia broadly, not the anaerobic subset specifically.
  3. Thin mechanistic evidence. The synergy mechanism rests largely on a single Prevotella intermedia/pneumococcus mouse–A549 model (PMID: 24478074); host transcriptomic/proteomic/metabolomic signatures are undefined.
  4. QoL data absent. No EQ-5D/SF-36/PROMIS measurements specific to anaerobic pneumonia were identified.
  5. Small/older bacteriology series. Several foundational studies are decades old and from single centers; susceptibility patterns and prevalence may have drifted.
  6. Treatment evidence is largely observational/experience-based. Head-to-head modern RCTs of antibiotic regimens for anaerobic pneumonia are lacking; the 80–90% cure figure derives from clinical experience/review (PMID: 20477271).
  7. Prevention evidence quality. Cochrane rated oral-care evidence as low quality with inconclusive incidence effects (PMID: 30264525).

Proposed Follow-up Experiments / Actions

  1. Prospective mNGS-based bacteriology cohort. Systematically apply comprehensive mNGS to BAL/pleural fluid in suspected aspiration/anaerobic pneumonia to quantify the true anaerobic contribution and re-test the "shift to Gram-negatives" hypothesis with detection method held constant.
  2. Host–microbe synergy mechanistics. Extend the Prevotella/PAFR model to additional anaerobe–aerobe pairs and to primary human airway organoids; test whether PAFR antagonism attenuates synergy and disease severity.
  3. Randomized antibiotic comparison. Modern RCT of clindamycin vs amoxicillin-clavulanate vs moxifloxacin (with mNGS-defined inclusion) to update regimen choice, including outcomes stratified by β-lactamase status.
  4. Oral-care prevention trial. Adequately powered RCT of intensive professional oral care + dysphagia rehabilitation in high-risk (stroke, dementia, LTC) populations, with pneumonia incidence and anaerobic-confirmed cases as endpoints, to resolve Cochrane uncertainty.
  5. Prognostic biomarker validation. Validate inflammatory indices (e.g., systemic immune-inflammation index; PMID: 42721055) and imaging severity features for risk stratification and early drainage decisions.
  6. Cross-species mechanism synthesis. Leverage canine megaesophagus/laryngeal-paralysis and equine pleuropneumonia cohorts as natural models to study the aspiration→anaerobic-infection continuum and test preventive interventions translatable to humans.

Report compiled from 10 confirmed findings and 51 reviewed papers across 5 investigation iterations. Evidence source types: predominantly human clinical (case series, cohorts, systematic reviews) and veterinary clinical; mechanistic evidence is in vitro (A549) and mouse model; no computational/omics host-profiling data were available for this disease.

Artifacts

Reference Validation

Checked with linkml-reference-validator 0.3.0rc1.

Outcome Count
References checked 38
Resolved 38
Unresolved (possible confabulation) 0
Unverifiable 0
Quoted claims checked 23
Quoted claims found in source 17
Quoted claims not found in source 6
References weighed for topical relevance 38
On topic 19
Off topic 0

Quotes not found in the cited source

Searched the abstract, any retrieved full text, and the title. A quote drawn from a part of the paper that was not retrieved will appear here too, so check before treating one as invented:

Every one of these was searched against an abstract alone, with no full text retrieved - marked abstract only below. Where full text can be fetched, re-running with it will settle them; where the source publishes only a summary to PubMed, as GeneReviews chapters do, it will not, and the quote has to be checked by hand against the chapter itself.

  • PMID:15824979 (abstract only): "Lung abscess due to K. pneumoniae was associated with underlying diabetes mellitus (odds ratio [OR], 4.3; 95% confidence interval [CI], 1.0–18.4; P = .039)"
  • closest text in source: "pneumoniae was associated with underlying diabetes mellitus (odds ratio [OR], 4.3; 95% confidence interval [CI], 1.0-18.4; P = .039) and negatively correlated with a time from onset of symptoms to diagnosis of >30 days (OR, 0.2; 95% CI, 0.1-0.7; P = .008)"
  • PMID:35271580 (abstract only): "The single-copy allele … strongly associated with CIM (P-val = 1.32×10⁻¹⁷)"
  • closest text in source: "The single-copy allele is strongly associated with CIM (P-val = 1.32x10-17), with homozygosity for this allele posing the most significant risk"
  • PMID:23398871 (abstract only): "anaerobic bacteriology is inadequate"
  • Text part not found as substring: 'anaerobic bacteriology is inadequate' (note: only abstract available for PMID:23398871, full text may contain this excerpt)
  • PMID:23398871 (abstract only): "Preferred antibiotics for these infections based on clinical experience are clindamycin and any beta-lactam–beta-lactamase inhibitor"
  • closest text in source: "Preferred antibiotics for these infections based on clinical experience are clindamycin and any betalactam-betalactamase inhibitor."
  • PMID:12959026 (abstract only): "metronidazole … amoxicillin/clavulanate, ampicillin/sulbactam, piperacillin/tazobactam, imipenem and clindamycin"
  • closest text in source: "Anaerobic bacteria are susceptible to metronidazole, tinidazole (exception of Gram-positive rods), amoxicillin/clavulanate, ampicillin/sulbactam, piperacillin/tazobactam, imipenem and clindamycin"
  • PMID:30264525 (abstract only): "NHAP is associated with poor oral hygiene and may be caused by aspiration of oropharyngeal flora into the lung. Oral care measures to remove or disrupt oral plaque might reduce the risk of NHAP"
  • closest text in source: "Oral care measures to remove or disrupt oral plaque might be effective in reducing the risk of NHAP"

Term Validation

Checked with linkml-term-validator 0.4.5, through the ols: adapter.

Outcome Count
Terms checked 37
Resolved 36
Unresolved (possible confabulation) 0
Obsolete 1
Unverifiable 0
Terms whose name was checked 23
Terms named correctly 8
Terms named as a different term 10
Terms whose name is worth a second look 5

Terms the report names something else

These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:

  • HP:0025406 (1 mention) - the report calls it "Fatigue-related"; HP calls it Asthenia
  • HP:0031246 (1 mention) - the report calls it "Purulent sputum"; HP calls it Nonproductive cough
  • HP:0025426 (1 mention) - the report calls it "Pulmonary cavity"; HP calls it Abnormal bronchus morphology
  • NCIT:C47384 (1 mention) - the report calls it "sulbactam"; NCIT calls it Albendazole
  • NCIT:C61785 (1 mention) - the report calls it "Broad, incl. Gram-negatives"; NCIT calls it Hydrocortisone Acetate
  • NCIT:C1741 (1 mention) - the report calls it "Anti-anaerobic fluoroquinolone"; NCIT calls it Chloride Ion
  • NCIT:C639 (1 mention) - the report calls it "Adjunct only (not monotherapy)"; NCIT calls it Mesylates
  • NCIT:C1602 (1 mention) - the report calls it "Severe/mixed/GNB"; NCIT calls it Saquinavir Mesylate
  • NCIT:C15311 (1 mention) - the report calls it "Preventive Intervention"; NCIT calls it Quality Control
  • NCIT:C15234 (1 mention) - the report calls it "Oral Hygiene"; NCIT calls it Follow-Up Study

Obsolete terms

These terms are real but deprecated. Citing one is not a fabrication; it does mean the report is naming something the ontology has retired:

  • GO:0070265 (obsolete necrotic cell death) (1 mention)

Terms whose name is worth a second look

The report's name for these is recognisably related to the term's own name without being one of them. A loose paraphrase reads the same way as a citation of the wrong sibling term - and so does a related synonym, which the ontology records precisely because it names something adjacent rather than the same thing - so these are listed rather than judged:

  • GO:0070265 (1 mention) - the report calls it "necrotic cell death"; GO calls it obsolete necrotic cell death
  • CL:0000066 (1 mention) - the report calls it "epithelial cell — alveolar/airway"; CL calls it epithelial cell
  • CL:0002063 (1 mention) - the report calls it "type II pneumocyte; A549 is a type-II-like line"; CL calls it pulmonary alveolar type 2 cell, and lists "type II pneumocyte" among its other names
  • NCIT:C376 (1 mention) - the report calls it "First-line"; NCIT calls it Cisplatin
  • NCIT:C29257 (1 mention) - the report calls it "amoxicillin"; NCIT calls it Miconazole Nitrate, and lists "Micatin" among its other names