High prevalence and diversity of tcdA-negative and tcdB-positive, and non-toxigenic, Clostridium difficile in Thailand.

Studies on the prevalence and diversity of Clostridium difficile in Thailand have been limited to those derived from a few tertiary hospitals in Central Thailand. In this study, 145 C. difficile isolates collected in 13 provinces in Thailand during 2006-2018 were characterized by ribotyping and detection of toxin genes. Minimum inhibitory concentrations of eight antimicrobial agents were determined also for all 100 C. difficile strains collected from 2006 until 2015. Of the 145 strains of C. difficile, 71 (49%) were non-toxigenic, 46 (32%) were toxin A-negative, toxin B-positive (A-B+) and 28 (19%) were A+B+. No binary toxin-positive strain was found. The most common ribotype (RT) was RT 017 (A-B+CDT-, 19%, 28/145). Besides RT 017, 20 novel non-toxigenic and A-B+ ribotyping profiles, which may be related to RT 017 by the similarity of ribotyping profile, were identified. All C. difficile strains remained susceptible to metronidazole and vancomycin, however, a slight increase in MIC for metronidazole was seen in both toxigenic and non-toxigenic strains (overall MIC50/90 0.25/0.25 mg/L during 2006-2010 compared to overall MIC50/90 1.0/2.0 mg/L during 2011-2015). There was a high rate of fluoroquinolone resistance among RT 017 strains (77%), but there was little resistance among non-toxigenic strains. These results suggest that RT 017 is endemic in Thailand, and that the misuse of fluoroquinolones may lead to outbreaks of RT 017 infection in this country. Further studies on non-toxigenic C. difficile are needed to understand whether they have a role in the pathogenesis of C. difficile infection in Asia.