THE OCCURRENCE, VIRULENCE, AND ANTIMICROBIAL RESISTANCE OF ANAEROBES IN POLYMICROBIAL INFECTIONS

Polymicrobial aerobic/anaerobic bacterial infections occur frequently and have been documented in most anatomic sites in the body. The etiol ogy of these infections is endogenous in that the normal microbial flo ra that colonize the various mucosal surfaces of the body can be isola ted from these infections after trauma to these membranes allowing the se organisms access to normally sterile sites. Subsequently, the organ isms begin to proliferate, causing extensive tissue damage. These infe ctions may spread to adjacent tissues or become loculated with abscess formation. In patients judged to have severe infection, surgery is of ten needed to debride the advancing spread of the infection, remove lo culated pus, and reestablish sufficient blood flow to deliver appropri ate antimicrobial agents to the infected site. Choice of antimicrobial agents should include agents with activity against both aerobes and a naerobes. Although a variety of anaerobes can be isolated from these i nfections, the Bacteroides fragilis group is the most clinically impor tant group of anaerobes because of the production of virulence factors and the high incidence of beta-lactamase production. Against the vari ous B. fragilis group species, metronidazole remains a very active age nt, whereas resistance rates to clindamycin are high among the non-B. fragilis species. Because of the good activity of many cephalosporin/c ephamycin agents against aerobic gram-negative bacteria and moderate t o good activity against anaerobes, these compounds remain as broad-spe ctrum choices for use in therapy of mixed infections. The addition of beta-lactamase inhibitors (tazobactam, sulbactam, or clavulanate) to v arious beta-lactam agents has increased their antimicrobial spectrum a gainst certain groups of aerobes, and particularly against beta-lactam ase-producing anaerobes, including the B. fragilis group. The choice o f single-agent therapy of mixed infections is ideally based on local d ata of susceptibility patterns of the various aerobes and anaerobes in volved in these infections.