PCR ribotyping and antimicrobial susceptibility testing of isolates of Clostridium difficile cultured from toxin-positive diarrheal stools of patients receiving medical care in Canadian hospitals: the Canadian Clostridium difficile Surveillance Study (CAN-DIFF) 2013-2015.

Clostridium difficile toxin-positive diarrheal stool specimens submitted to eight Canadian hospital laboratories from 2013 to 2015 were cultured. Polymerase chain reaction ribotyping of isolates was performed using an internationally standardized, high-resolution capillary gel-based electrophoresis protocol and antimicrobial susceptibility testing conducted by CLSI-defined agar dilution (M11-A8, 2012). Among the 1310 isolates of C. difficile cultured, 141 different ribotypes were identified; the most common ribotypes were 027 (24.5% of isolates), 014 (7.7%), 020 (6.6%), 106 (6.1%), and 002 (4.6%). Ribotype 027 was the commonest ribotype in all geographic regions of Canada and was more frequently isolated from patients aged ≥80 years (40.6%) than younger patients (P<0.00001). Ribotype 027 isolates were frequently moxifloxacin-resistant (92.2% of isolates) and multidrug-resistant (49.5%). Fidaxomicin demonstrated the greatest in vitro potency (lowest MIC90, 0.5 μg/mL; lowest maximum MIC, 2 μg/mL) of eight antimicrobial agents tested and was the most active agent against each of the five commonest ribotypes (MIC90, 0.25-1 μg/mL).