In vitro susceptibility of common clinical anaerobic and aerobic isolates against josamycin.

The in vitro susceptibility of 145 anaerobic clinical isolates and 96 gram-positive aerobic clinical isolates to josamycin, a new macrolide antibiotic, was studied using the agar dilution technique. Ninety-five of the aerobes were susceptible to 1.56 mug or less of josamycin per ml. The median minimal inhibitory concentration of these organisms was </=0.39 mug/ml. The in vitro activity of josamycin against the anaerobes was compared with that of erythromycin, clindamycin, penicillin, and chloramphenicol. At concentrations </=3.12 mug/ml, 100% of strains of Bacteroides species and Bacteroides fragilis were susceptible to josamycin. At low concentrations (</=0.39 mug/ml), clindamycin was more active than josamycin against the anaerobes. However, at concentrations </=3.12 mug/ml, the activities of josamycin and clindamycin were similar except against the Fusobacterium species, which was quite resistant to josamycin.