The beta-lactamases of genus Bacteroides

Two hundred anaerobic isolates from clinical specimens were examined for beta-lactamase production by Nitrocefin methodology. Altogether, 77 strains were beta-lactamase producers. Organisms belonging to Bacteroides melaninogenicus group, i.e., B. intermedius and B. bivius, were found to have a significant frequency of beta-lactamase production. Substrate profile and sensitivity to the beta-lactamase inhibitors, sulbactam, clavulanic acid, cloxacillin, and cefmetazole, a cephamycin derivative, were determined for these enzymes. All enzymes hydrolyzed cephalosporins more rapidly than penicillins. Cefmetazole was not hydrolyzed at all. Strains of B. fragilis, B. thetaiotaomicron, B. uniformis, B. ovatus and B. oralis produced beta-lactamases sensitive to all four inhibitors. Strains of B. intermedius, B. bivius and B. disiens produced enzymes of different nature which were inhibited only by cefmetazole. B. vulgatus enzyme was inhibited by three of the four inhibitors. These results suggest that the beta-lactamases of the genus Bacteroides may be classified by substrate profile and inhibitor pattern.