Infections due to anaerobic bacteria and the role of antimicrobial susceptibility testing of anaerobes

Anaerobic bacteria are the predominating indigenous flora of man and, as a result, play an important role in infections, some of which are serious wit h a high mortality rate. These opportunistic pathogens are frequently misse d in cultures of infected materials because of shortcomings in collection a nd transport procedures. Antimicrobial resistance among anaerobes, particul arly members of the Bacteroides fragilis group, is a significant factor in the selection of agents for both treatment of clinical infections and for s urgical prophylaxis in anatomic settings where anaerobes represent a majori ty of the usual flora. Striking geographic and hospital-specific difference s in susceptibility patterns related to antibiotic prescribing habits have been reported in recent studies. Resistance to agents within all useful ant ibiotic classes has been reported in the Bacteroides spp. Among these speci es beta -lactamase production is the primary mechanism of resistance to the penicillins and cephalosporins. In most eases this resistance is obviated by the addition of a beta -lactamase inhibitor to the otherwise hydrolysed beta -lactam agent; e.g. sulbactam to ampicillin or clavulanate to ticarcil lin. Ribosomal protection, clindamycin resistance by ribosomal modification , and metronidazole resistance to tetracyclines is mediated by ribosomal pr otection, clindamycin resistance by ribosomal modification, and metronidazo le resistance by a complex combination of events. Especially disturbing rep orts of resistance to multiple antibiotic agents in the same isolate have b een published recently. An understanding of the mechanisms of resistance to antibiotics by these organisms and the mode of spread of such resistance m ay lead to a more informed selection of agents for treatment and prevention of anaerobic infections. (C) 2001 Lippincott Williams & Wilkins.