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Anaerobic bacteria are the greatest component of the human body's normal bacterial flora colonizing the skin, oral cavity, and genitourinary and lower gastrointestinal tracts. Their presence is important in preserving vitamin and other nutrient absorption and in preventing infection with pathogenic bacteria.
Anaerobes generally are of low pathogenicity but may possess virulence factors such as endotoxin or polysaccharide capsules or produce extracellular toxins. Disease occurs when a large inoculum develops in an area lacking oxygen and/or poor blood supply.
Typical anaerobic infections include periodontitis, abdominal or pelvic abscesses, endometritis, pelvic inflammatory disease, aspiration pneumonia, empyema and lung abscesses, sinusitis, brain abscesses, gas gangrene, and other soft tissue infections. Many Bacterioides produce beta-lactamase and are resistant to penicillins and cephalosporins. Imipenem, metronidazole, and clindamycin are effective agents although resistance to clindamycin is increasing.
Diagnosing anaerobic bacterial infections
Isolation of anaerobes in significant numbers from well collected specimens including blood, other normally sterile body fluids, or closed collections of purulent fluid indicates infection with that (those) organism(s).
Specimens should be collected by needle and syringe aspiration or surgical drainage to avoid contamination with normal-flora anaerobes; such contamination would make interpretation of culture results impossible.
Specimens must be transported in anaerobic transport vials.
Finegold SM, George WL: Anaerobic Infections in Humans. San Diego, CA, Academic Press, 1989