Antimicrobial susceptibility and heteroresistance in Chinese Clostridium difficile strains.

One hundred and ten toxigenic Clostridium difficile isolates collected between December 2008 and May 2009 at Fudan University Hospital Huashan were analyzed for their antibiotic susceptibility patterns and resistance molecular basis. The heteroresistance to metronidazole in fresh isolates were detected as well. Sixteen different PCR ribotypes were identified with a dominant clone 017 accounting for 37.3% of the isolates, followed by 001 and H. Ribotype 027 was not found but one isolate belonged to ribotype 078. All the isolates were susceptible to vancomycin and piperacillin/tazobactam. Seventy-eight fresh isolates were tested for heteroresistance to metronidazole, 18 (23.1%) of them were found to be positive. Resistance to moxifloxacin, ciprofloxacin, levofloxacin, erythromycin, clindamycin, tetracycline, rifampin, rifaximin and fusidic acid was found in 61.8%, 100%, 66.4%, 85.3%, 88.1%, 62.7%, 29.1%, 29.1% and 8.2% of the isolates, respectively. The isolates of common PCR ribotypes were more frequently resistant than the uncommon ribotypes. The prevalence of resistance genes and mutations among the resistant isolates was as follows: ermB, 69.1%; tetM, 97.1%; gyrA mutation, 63.2%; gyrB mutation, 4.4%; gyrA and gyrB mutation, 32.4%; rpoB mutation, 100%, respectively. The resistance related fusA mutation was only found in one isolate with minimum inhibitory concentration of 4 mg/L.