Comparison of agar dilution and broth microdilution methods for Clostridium difficile antimicrobial susceptibility testing.

In this study, the performance of the broth microdilution (BMD) method for testing the antimicrobial susceptibility of Clostridium difficile in comparison with the agar dilution (AD) method used by the Clinical and Laboratory Standards Institute (CLSI) was evaluated. In total, 70 non-duplicate C. difficile clinical isolates were used in this study. The minimum inhibitory concentrations (MICs) of clindamycin, moxifloxacin, metronidazole and vancomycin were examined using AD and BMD. The results showed that BMD is acceptable for routine antimicrobial susceptibility testing of C. difficile as its performance was comparable with that of the AD method. In addition, it was noted that metronidazole- and vancomycin-resistant isolates are extremely rare in Japan.