TIME-DEPENDENT KILLING OF CLOSTRIDIUM-DIFFICILE BY METRONIDAZOLE AND VANCOMYCIN

Killing of Clostridium difficile by metronidazole and vancomycin was studied with a batch culture method. Pre-reduced 50 ml volumes of brain heart infusion broth containing one of a range of concentrations of either vancomycin or metronidazole were inoculated with approximately 106 cfu/ml of C. difficile. The cultures were incubated anaerobically at 35°C for 24 h. Total viable counts and spore counts were performed with a modified Miles and Misra technique. Concentrations of metronidazole and vancomycin below the respective MICs had no effect on the growth of C. difficile. significant reduction in numbers of vegetative cells and spores occurred in the presence of concentrations of both agents close to their respective MICs. A bacteriostatic effect was observed when vancomycin concentrations similar to those occurring in faeces following oral administration of the drug were used. In contrast, rapid killing of vegetative cells occurred over a wide range of metronidazole concentrations greater than the MIC. © 1991 The British Society for Antimicrobial Chemotherapy.