Antimicrobial activity of fidaxomicin against Clostridium difficile clinical isolates in Aichi area in Japan.

We evaluated the susceptibility of 100 Japanese Clostridium difficile isolates to fidaxomicin, a new macrocyclic antibiotic. The minimum inhibitory concentration (MIC) range of fidaxomicin was 0.03-0.5 μg/mL, with a MIC for inhibition of 50% (MIC50) of 0.12 μg/mL, and for inhibition of 90% (MIC90) of 0.25 μg/mL. We also evaluated the susceptibilities of the same 100 C. difficile isolates to vancomycin, metronidazole, moxifloxacin, clindamycin, meropenem, and ampicillin. Of all the antibiotics tested, fidaxomicin showed the most potent antimicrobial activity against this group of C. difficile isolates. MIC levels against C. difficile isolates, including those producing binary toxin, did not substantially differ from those previously reported in Europe, North America and Taiwan.