Antimicrobial susceptibility of Clostridium difficile determined by disc diffusion and breakpoint methods.

The susceptibility of 160 isolates of Clostridium difficile to eight antimicrobial agents was studied by two methods. There was generally good agreement between the results obtained with the disc diffusion and breakpoint methods. More than 90% of isolates studied were considered sensitive by both methods. However there was a major difference between the results obtained with the two methods for penicillin G and clindamycin, resistance to both agents being overestimated by the disc diffusion method. Several isolates exhibited multiple resistance to penicillin G, tetracycline, erythromycin and clindamycin. All isolates were inhibited by both metronidazole and vancomycin. None of the isolates produced beta-lactamase.