Bettina Knoll (E. Mylonakis, Editor)
- Anaerobic infections are caused by bacteria that require reduced oxygen for growth.
- Anaerobes associated with human infections are aero-tolerant: They can survive, but not replicate, for up to 72 hours in an oxygenated atmosphere.
- Anaerobic bacteria colonize mucosal membranes and predominate in infections arising from mucosal and adjacent sites.
Anaerobes account for up to 10% of blood culture isolates from patients with clinically significant bacteremia (1). No incidence data is available for anaerobic infections of other sites.
- Mucosal barrier breakdown secondary to neoplasm, chemotherapy, radiation, neutropenia, graft versus host disease, surgery, trauma, inflammatory bowel disease, diverticulitis, appendicitis
- Poor dental hygiene
- Altered mental status, depressed gag reflex, impaired swallowing
- Bowel preparation and perioperative antimicrobial prophylaxis
- Good dental hygiene
- Aspiration precautions
- Translocation of resident flora into sterile sites due to breakdown of mucosal membranes
- Translocation of oral flora into lungs due to aspiration
- Proliferation of obligate anaerobes during polymicrobial infection due to lowered oxidation–reduction potential by aerobic organisms
- Virulence factors enable anaerobic bacteria to induce abscess formation (e.g., Bacteroides fragilis: Capsular polysaccharide), to evade host defenses (e.g., Prevotella: IgA proteases), to adhere to cell surfaces (e.g., Porphyromonas gingivalis: Proteases), and to produce toxins and/or enzymes (e.g., Fusobacterium necrophorum: Leukotoxin and endotoxin)
- B. fragilis is the most common isolated anaerobic Gram-negative bacillus. Other Gram-negatives are Fusobacterium, Prevotella, and Porphyromonas species.
- Peptostreptococcus species are the major Gram-positive cocci, and Clostridia is the main Gram-positive rods causing disease.
COMMONLY ASSOCIATED CONDITIONS 
- Dental infections
- Pulpitis
- Periapical and dental abscess
- Perimandibular space infection
- Gingivitis
- Periodontitis
- Periodontal abscess
- Extension of periodontal infection with maxillary sinus osteomyelitis or submandibular space infection
- Vincent's stomatitis (trench mouth)
- Ludwig's angina: Bilateral infection of the sublingual and submandibular spaces
- Lemierre Syndrome: F. necrophorum infection of the posterior compartment of the lateral pharyngeal space complicated by suppurative thrombophlebitis of the jugular vein and secondary metastasis, primarily to the lungs
- Chronic sinusitis and otitis media
- Pleuropulmonary infections
- Aspiration pneumonia
- Necrotizing pneumonia
- Lung abscess
- Empyema
- Intraabdominal infections
- Peritonitis
- Abscesses
- Neutropenic colitis (Typhlitis)
- Female genital tract infections
- Pelvic inflammatory disease
- Pelvic abscess
- Septic abortion
- Endometritis
- Tubo-ovarian abscess
- Postoperative infection
- Bacterial vaginosis
- Pelvic cellulitis
- Amnionitis
- Septic thrombosis of pelvic veins
- Central nervous system infections
- Cerebral abscess
- Epidural abscess
- Subdural empyema
- Anaerobic meningitis: Rare, suggestive of shunt infection or parameningeal collection
- Skin and soft tissue
- Necrotizing fasciitis
- Gas gangrene
- Crepitant cellulitis
- Bite wounds
- Surgical wounds
- Diabetic foot infection
- Decubitus ulcers
- Bone and joint
- Osteomyelitis and septic arthritis adjacent to infected soft tissue sites
- Bacteremia
- Secondary to an intraabdominal/genital tract/respiratory tract/soft tissue infection
- B. fragilis most common isolate
-Lactam/
