Anaerobic infections: diagnosis and treatment

Anaerobic bacteria outnumber aerobic bacteria in normal flora in the oropharynx and gastrointestinal tract. They are important and frequent causes of infection, although they often go unrecognized except in the classic and very distincitve clostridial infections and intoxications-gas gangrene, botulism, and tetanus. Although anaerobic infections often originate close to a muscosal surface where anaerobes are part of the normal flora, they may occur anywhere in the body via direct of hematogenous spread. Clues to diagnosis include a foul-smelling discharge, gas, necrotic tissue, abscess formation, the unique morphology of certain anaerobes on Gram's Stain, and failure to obtain growth on aerobic culture despite the presence of organisms on Gram-stained direct smear. Predisposing conditions include aspiration, vascular insufficiency, trauma, malignancy, and previous antimicrobial therapy. Clinical suspicion requires confirmation of diagnosis by appropriate collecting, transport and culturing of specimens while excluding contamination with anaerobes from the normal flora. Treatment usually requires a combination of surgical and medical measures. Penicillin G is the drug of choice for virtually all anaerobic infections except those caused by Bacteroides fragilis, which require chloramphenicol or clindamycin. Investigational agents also appear promising in the treatment of anaerobic infections.