Genotypic and phenotypic analysis of Clostridium difficile correlated with previous antibiotic exposure.

To analyze Clostridium difficile susceptibility results and genotypes in relation to antibiotic exposures that precipitated C. difficile-associated diarrhea (CDAD), we examined 83 nosocomial C. difficile isolates recovered at a tertiary care center in Boston, Massachusetts. MICs were determined by E-test methodology using modified Brucella agar. Isolates were genotyped by pulsed-field gel electrophoresis and restriction enzyme analysis. Antibiotic susceptibilities were: ciprofloxacin (0%), clindamycin (59%), trovafloxacin (63%), ceftriaxone (73%), piperacillin/tazobactam (100%), metronidazole (100%), and vancomycin (100%). The two most common strain groups, isolated from a total of 33 patients, were much more likely to be resistant to clindamycin, erythromycin, and trovafloxacin than other strain groups [79% (26 of 33) versus 2% (1 of 50), respectively]. Clindamycin exposure was strongly associated with CDAD caused by isolates that exhibited multiple resistance to clindamycin, erythromycin, and trovafloxa...