Antimicrobial susceptibility of relatively infrequent isolates of the Bacteroides fragilis group: Bacteroides uniformis, bacteroides caccae, and Bacteroides eggerthii

Abstract

Using a broth microdilution method, clinical isolates of Bacteroides caccae (10 strains), Bacteroides eggerthii (1 strain), and Bacteroides uniformis (25 strains) were tested to determine their susceptibility to various beta-lactam agents, clindamycin, and metronidazole. All strains were beta-lactamase producers. Strains of B uniformis exhibited the highest incidence of resistance. Among the cephalosporins, ceftizoxime and cefoperazone had minimum inhibitory concentration (MIC 90) values of 64 g/ml with 16% and 12% resistance rates, respectively, and were more active than cefotaxime (MIC 90 ⩾ 128 g/ml). For the cephamycins, cefoxitin was more active than cefotetan. Strains resistant to ticarcillin, mezlocillin, piperacillin, and clindamycin were also detected. No resistance was detected to piperacillin/tazobactam, cefoperazone/sulbactam, ampicillin/sulbactam, imipenem, or metronidazole. Strains of B caccae were susceptible to all the test agents except for a single strain resistant to all beta-lactams alone (except imipenem) and clindamycin. The single strain of B eggerthii was susceptible to all of the antimicrobial agents. These data indicate that the infrequently isolated strains of the B fragilis group produce beta-lactamase and exhibit a diversity of antibiograms.