Beta-lactamase activity of anaerobic bacteroides strains isolated from clinical samples and their susceptibility to antimicrobial agents.

Beta-lactamase production and susceptibility to 13 antimicrobial agents (penicillin-G, amoxycillin, amoxycillin/clavulanic acid, cefoxitin, imipenem, clindamycin, metronidazole, piperacillin, ticarcillin, rifampicin, chloramphenicol, tetracycline and erythromycin) of 32 isolated Bacteroides strains were determined. The strains included 23 isolates of B. frugilis, 2 B. thetaioatomicron, 2 B. ovatus, 1 B. distasonis, 1 B. capillosus, 1 B. uniformis, 1 B. ureolyticus and 1 B. merdae. beta-Lactamase production was detected in 65% of the Bacteroides using the nitrocefin test, All the antibiotic agents showed excellent activity against beta-lactamase negative strains (for tetracycline, ticarcillin and clindamycin, 90% were susceptible, whereas for the other drugs, 100% were susceptible). beta-Lactamase-positive Bacteroides strains showed 95% susceptibility to metronidazole and rifampicin; 90% susceptibility to piperacillin and cefoxitin; 85% susceptibility to tetracycline and erythromycin; 80% susceptibility to clindamycin and amoxycillin/clavulanic acid, and 76% susceptibility to ticarcillin. All beta-lactamase-positive strains were found to be susceptible to imipenem and chloramphenicol.