Comparative susceptibility of the Bacteroides fragilis group species and other anaerobic bacteria to meropenem, imipenem, piperacillin, cefoxitin, ampicillin/sulbactam, clindamycin and metronidazole

The in-vitro activity of meropenem, imipenem, piperacillin, cefoxitin, ampicillin/ sulbactam, clindamycin and metronidazole was determined against 395 strains of strict and facultative anaerobes, including Gardnerella vaginalis, Lactobacillus spp. and Mobiluncus spp. The activities of meropenem and imipenem were within one dilution of their MIC50 and MIC90 values. One isolate of Bacteroides fragilis, two of Bacteroides distasonis, and two of Bacteroides ovatus showed resistance or diminished susceptibility to meropenem and imipenem. Metronidazole was active against almost all obligate anaerobic isolates. Some non-spore-forming Gram-positive bacilli and lactobacilli were resistant. Ampicillin/sulbactam inhibited almost all isolates at ≤16/8 mg/L. The activity of clindamycin and cefoxitin was relatively good, but some strains of non-fragilis B. fragilis group species were resistant. Piperacillin was the least active agent tested.