The emergence of metronidazole and vancomycin reduced-susceptibility in Clostridium difficile isolates in Iran.

OBJECTIVES: Clostridium difficile is the main causative agent of antibiotic-associated diarrhoea (AAD) and pseudomembranous colitis (PMC). The accumulation of antimicrobial resistance in C. difficile strains can drive Clostridium difficile infection (CDI) epidemiology. This study was undertaken in order to evaluate the antimicrobial resistance patterns of toxigenic C. difficile isolates cultured from diarrhoeal stool samples of hospitalised patients with suspected CDI in three tertiary care hospitals in Tehran, Iran.

METHODS: Two hundred and fifty diarrhoeal stool samples were investigated by toxigenic culture using cycloserine-cefoxitin-fructose agar and the VERO cell line. Antimicrobial susceptibility to metronidazole, vancomycin, clindamycin, tetracycline, and moxifloxacin was performed by disk diffusion and E-test methods on Brucella Blood Agar supplemented with hemin and vitamin K.

RESULTS: Thirty-five stool samples (14.0%) proved positive using C. difficile toxigenic culture. According to CLSI breakpoints, the following resistance was identified in C. difficile isolates: metronidazole (2/35); moxifloxacin (7/35); clindamycin (18/35); and tetracycline (5/35). Using EUCAST breakpoints, 3/35 isolates showed reduced-susceptibility for vancomycin and 14/35 for metronidazole. In addition, the results showed a good correlation between the inhibition zone diameter (disk diffusion) and MIC values (E-test); Pearson correlation coefficient 0.7400.95, P<0.001.

CONCLUSIONS: Multidrug resistance was observed in Iranian clinical toxigenic C. difficile isolates, including reduced-susceptibility to first-line CDI treatment drugs. I addition, disk diffusion can be used as cost-effective option for the antimicrobial susceptibility testing of C. difficile isolates.