In vitro activity of tigecycline against Bacteroides species

To ascertain the current susceptibility patterns of members of the Bacteroides fragilis group in our hospital and to assess the in vitro activity of tigecycline against these organisms.

A total of 400 non-duplicate clinical isolates of the B. fragilis group collected from 2000 to 2002 were studied. Susceptibility testing was performed according to the reference agar dilution method described by the NCCLS. The following antimicrobials were tested: tigecycline, clindamycin, metronidazole, chloramphenicol, cefoxitin, imipenem, amoxicillin-clavulanate and piperacillin-tazobactam.

All strains were susceptible to metronidazole and chloramphenicol. For clindamycin and cefoxitin, the overall susceptibility rates were 59.5% and 83%, respectively. Imipenem and piperacillin-tazobactam were the most active beta-lactam agents tested. Tigecycline inhibited 89.8% of the strains at a concentration of 8 mg/L with an MIC range of 16 mg/L. By comparing the MIC50 and MIC90 values of tigecycline among the various species of the group, B. fragilis, Bacteroides thetaiotaomicron and Bacteroides vulgatus were the most susceptible (MIC50/MIC90s of 0.5-1/8 mg/L).

Tigecycline exhibited activity against most isolates of the B. fragilis group tested. These results indicate that tigecycline may be useful in the treatment and prophylaxis of infections involving these organisms.