Comparison of Spore Germination Rate between Toxigenic and Nontoxigenic Clostridium difficile Isolates in the ½ × MIC of Ceftazidime alone and in Combination with Clindamycin and Vancomycin

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.

Keywords:

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