Comparison of in vitro susceptibilities of Bacteroides and Fusobacterium species in inland southern California to published patterns as a guide to empiric therapy.

Anaerobic bacteria, particularly the Bacteroides group, are becoming increasingly resistant to antimicrobials. Anaerobic susceptibility testing is often not done routinely in clinical laboratories, causing clinicians to depend on national survey results or susceptibility patterns published by different centers. In this study, we have determined anaerobic susceptibility patterns of 200 clinical isolates of anaerobic gram-negative bacilli from four hospitals in the inland countries of southern California (Inland Empire). Of 11 antibiotics tested, metronidazole and chloramphenicol were the most active, with no resistance noted, followed by imipenem, ticarcillin/clavulanate, and ampicillin/sulbactam. Among cephalosporins, cefoxitin was the most active and cefotetan the least. Significant differences in the susceptibility pattern to cefoxitin were observed in one hospital. Differences between our inland patterns and those for Los Angeles Wadsworth VA Hospital were seen for cefoxitin in the B fragilis group and piperacillin for B fragilis. We confirmed the National Committee for Clinical Laboratory Standards (NCCLS) recommendation for periodic determination of anaerobic susceptibility patterns. We also suggest that clinical laboratories routinely identify anaerobes to the species level to facilitate clinical application of in vitro results.