Anaerobic or mixed anaerobic-aerobic pulmonary infection is important both in community-acquired disease and in the hospital setting. Its principal c… - Sydney M. Finegold

Anaerobes are prevalent on all mucosal surfaces and virtually all anaerobic infections are endogenous. Two thirds of anaerobic infections involve five anaerobic organisms or groups—the Bacteroides fragilis group, the Bacteroides melaninogenicus-Bacteroides asaccharolyticus group, Fusobacterium nucleatum, the anaerobic cocci, and Clostridium perfringens. Conditions that lower the oxidation-reduction potential and disrupt the mucosal surface (eg, vascular problems, malignant neoplasms, and surgery) lead to infection with anaerobes. Clues to anaerobic infection include foul odor, gas, tissue destruction, underlying malignant neoplasms, and the unique appearance of certain anaerobes on Gram's stain. Specimens must be collected to avoid normal flora and transported to the laboratory under anaerobic conditions. Therapy involves surgical débridement and drainage and the use of various antimicrobial agents. Antimicrobial agents must be used for extended periods to avoid relapse.

Several classes of antimicrobial agents (e.g., penicillins, cephalosporins, tetracyclines, chloramphenicol, and clindamycin) are useful in treatment of infections due to anaerobic bacteria. However, certain anaerobic bacteria have shown a striking resistance to antimicrobial agents. In vitro susceptibility tests are useful for selection of optimal therapy. The choice of agent depends, to some extent, on the organisms responsible for the infection. Bacteroides fragilis is the most commonly encountered anaerobe, and it is also the most resistant to antimicrobial agents. Other factors influencing the selection of therapy include pharmacologic characteristics, degree of bactericidal activity, and toxicity. Proper therapy for anaerobic infections often requires intensive antimicrobial therapy for a prolonged period. Surgical intervention, including drainage of abscesses and excision of necrotic tissue, is important.

The commonly used drugs that have a major effect on the colonic flora are ampicillin, cefoperazone, clindamycin and oral neomycin or kanamycin, used together with either tetracycline, erythromycin or metronidazole.