In Vitro Susceptibility of Common Clinical Anaerobic and Aerobic Isolates Against Josamycin

Abstract

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 μg or less of josamycin per ml. The median minimal inhibitory concentration of these organisms was ≤0.39 μg/ml. The in vitro activity of josamycin against the anaerobes was compared with that of erythromycin, clindamycin, penicillin, and chloramphenicol. At concentrations ≤3.12 μg/ml, 100% of strains of Bacteroides species and Bacteroides fragilis were susceptible to josamycin. At low concentrations (≤0.39 μg/ml), clindamycin was more active than josamycin against the anaerobes. However, at concentrations ≤3.12 μg/ml, the activities of josamycin and clindamycin were similar except against the Fusobacterium species, which was quite resistant to josamycin.