Epidemiology and susceptibility of resistant Bacteroides fragilis group organisms to new beta-lactam antibiotics.

The epidemiology of the Bacteroides fragilis group and the interspecies frequencies of antibiotic resistance were examined. Susceptibilities were determined for 16 beta-lactam antibiotics, including seven new compounds. Fourteen percent of 287 patients with infection due to organisms of the B. fragilis group presented with bacteremia. Infections were as common among pediatric patients as among patients on the surgical services. Clindamycin resistance varied from 3% to 22% among the species. Resistance to clindamycin and cefoxitin was more likely to be encountered among Bacteroides species other than B. fragilis. These organisms were more commonly recovered from surgical wound specimens. Only N-formimidoylthienamycin showed predictably good activity against Bacteroides resistant to clindamycin or cefoxitin. The other new beta-lactam antibiotics had variable activities against these resistant strains, and significant differences were noted overall among the antimicrobial agents tested. Early speciation and susceptibility testing of clinical isolates of the B. fragilis group are needed, particularly if newer agents with unpredictable activities are used.