In vitro susceptibility of clinical isolates ofBacteroides fragilis andBacteroides thetaiotaomicron in Japan

A nationwide survey of the susceptibility of 433 isolates ofBacteroides fragilis and 149 isolates ofBacteroides thetaiotaomicron was conducted from December 1986 through November 1989 in Japan. These strains were collected from 16 university hospitals and one metropolitan hospital. Metronidazole was the most active drug against both species, with no resistant isolates found. The activity of imipenem and sulbactam-cefoperazone was good, with very low resistance rates determined inBacteroides fragilis (1.4 % and 1.6 %, respectively) and inBacteroides thetaiotaomicron (3.4 % for both drugs), and was comparable to that of metronidazole. Cefoxitin, cefmetazole, cefotetan, cefbuperazone, latamoxef and ceftizoxime were found to be more active againstBacteroides fragilis, for which resistance rates were 3.2 to 9.5 %, than againstBacteroides thetaiotaomicron, for which resistance rates were 18.1 to 21.8 %. Rates of piperacillin resistance in the two species were 12.9 % and 26.8 %, respectively. Clindamycin was very active at a low concentration (MIC50 of 0.39 to 1.56 mg/l), but 24 % and 27.5 % ofBacteroides fragilis andBacteroides thetaiotaomicron isolates, respectively, were resistant to this agent.