Belgian Collaborative Study of the in-vitro susceptibility of the Bacteroides fragilis group. A Belgian Collaborative Study Group.

The antimicrobial susceptibility of clinical isolates of the Bacteroides fragilis group obtained from nine large Belgian university and community hospitals was studied. Of the beta-lactam antibiotics tested, none were active against 100% of the isolates. Piperacillin was active against 93% of the strains at a breakpoint of 64 micrograms/ml. The percentage of isolates inhibited at 16 micrograms/ml (and 32 micrograms/ml) for the 7-alpha-methoxy antibiotics was: cefoxitin 84; latamoxef 87; and cefotetan 64. B. fragilis tended to be more susceptible to all beta-lactams than the other members of the group. Among the non beta-lactam antibiotics, the resistance rate for minocycline, doxycycline, clindamycin and erythromycin (at a breakpoint of 4 micrograms/ml) were 1%, 4%, 14% and 34%, respectively. Like the beta-lactams, clindamycin was less active against non B. fragilis species of the group. Chloramphenicol, metronidazole and tinidazole were still active against 100% of the isolates at their breakpoint values (8 micrograms/ml).