Anaerobes in polymicrobial surgical infections: incidence, pathogenicity, and antimicrobial resistance.

Many types of anaerobic bacteria have been isolated from clinical infections. Although most of these infections are polymicrobial and involve facultative Gram-negative bacilli, some are strictly anaerobic. For most of them, surgical intervention such as drainage of an abscess and debridement of devitalised tissue is the primary treatment and re-establishes good blood flow to the affected area. Appropriate antimicrobial treatment is also important to kill both residual organisms and those that may have spread from the site of primary infection. Several groups of anaerobes (for example, Bacteroides fragilis group, Prevotella, Porphyromonas, and Fusobacterium) have developed mechanisms of resistance to beta-lactam agents, the most common of which is production of beta-lactamases. A recent approach to neutralising these enzymes has been to combine the beta-lactam agent with an irreversible beta-lactamase inhibitor. Because of their potency against both aerobes and anaerobes, these combinations may replace traditional combination treatment (gentamicin/clindamycin) for polymicrobial infections. Piperacillin/tazobactam was the beta-lactam/beta-lactamase combination that was most active against the B fragilis group in the present study.