Ebrahim Rezazadeh Zarandi - Immunology of Infectious Diseases Research Center, Research Institute of Basic Medical Sciences, Rafsanjan University of Medical Sciences, Rafsanjan, Iran
Shahla Mansouri - Department of Microbiology and Virology, Faculty of Medicine, Kerman University of Medical Sciences, Kerman, Iran
Farhad Sarafzadeh - Department of Infectious Diseases, Afzalipour Hospital, Kerman University of Medical Sciences, Kerman, Iran
Nouzar Nakhaee - Kerman Neuroscience Research Center, Kerman University of Medical Science, Kerman, Iran
Mohammad Moradi - Department of Microbiology and Virology, Faculty of Medicine, Kerman University of Medical Sciences, Kerman, Iran

Introduction and Objectives: Germination of spore in Clostridium difficile (C. difficile) can be occurred in the presence of some antibiotics. The aim of this study was to compare the spore germination rate in toxigenic and nontoxigenic isolates in the sub-MIC of ceftazidime alone and in combination with clindamycin and vancomycin.Materials and Methods: The MIC and FIC of C. difficile isolates were performed by microdilution and checkerboard microdilution method, respectively. About 106 CFU/mL spores were inoculated to pre-reduced medium with ½ × MIC of each antibiotic alone and ½ × FIC in combination. The number of remaining spores were counted after 24 hours by viable spore count/mL. Results: The ungerminated spores’ rate were different between toxigenic and nontoxigenic isolates. The toxigenic isolates of C. difficile germinated more than nontoxigenic isolates at ½ × MIC and ½ × FIC of antibiotics. All isolates (toxigenic and non-toxigenic) of C. difficile germinated at ½ × MIC of ceftazidime. Conclusion: The rate of toxigenic isolates are increasing at the presence of some particular antibiotics. So that the nontoxigenic isolates are replaced by toxigenic ones, and as a result, the rate of C. difficile associated diarrhea is increased.

Clostridium difficile, Spore germination, sub-MIC, Antibiotics, Combination