Variation in the susceptibility of Bacteroides fragilis group isolates from six Chicago hospitals.

The antimicrobial susceptibility of isolates of the Bacteroides fragilis group from six hospitals in the Chicago area varied from one institution to another; this variation was similar to the geographic variation documented in a national survey. A total of 365 B. fragilis group isolates were tested against 10 antibiotics. Imipenem, piperacillin/tazobactam, ampicillin/sulbactam, ticarcillin/clavulanate, and cefoperazone/sulbactam had excellent activity against all members of the B. fragilis group, with little interhospital variation. Cefoxitin and ceftizoxime had very good activity, also with little variation among hospitals. Clindamycin, cefotetan, and cefmetazole had the lowest level of activity, with unusually high-level resistance confined to three of the six hospitals. These data indicate that variation in the antimicrobial susceptibility of these bacteria is likely based in the hospital rather than in the geographic region and that the in vitro activity of certain antibiotics against B. fragilis group isolates from individual hospitals cannot be predicted from the data obtained in larger-scale surveys.