Antimicrobial susceptibilities of Clostridium difficile isolated in Japan

Clostridium difficile is a common causative organism of antimicrobial-associated diarrhea and is often responsible for nosocomial infection. C. difficile infection has traditionally been treated with metronidazole (MNZ) or vancomycin (VCM); however, MNZ-resistant strains have reported in some countries. In this study the broth microdilution method was used to determine the minimum inhibitory concentrations (MICs) of 15 drugs against 157 clinical isolates of C. difficile in Japan. All C. difficile isolates tested were susceptible to MNZ; MIC₅₀ was 0.25 μg/ml, MIC₉₀ was 0.5 μg/ml, and MIC range was 0.06-1 μg/ml. C. difficile isolates were also susceptible to VCM; MIC₅₀ was 0.5 μg/ml, MIC₉₀ was 1 μg/ml, and MIC range was 0.12-2 μg/ml. Susceptibility to teicoplanin was also similar: MIC₅₀ was 0.12 μg/ml, MIC₉₀ was 0.12 μg/ml, and MIC range was 0.03-0.25 μg/ml. The susceptibility of C. difficile isolates must be monitored continuously because a strain with reduced susceptibility to MNZ or VCM might emerge in the future.