Clostridium difficile, a spore-forming anaerobe, causes toxin-mediated diarrhoea and pseudomembranous colitis, primarily among hospital inpatients. Some of the most severe outbreaks of C. difficile infection (CDI) have been caused by strains with enhanced antimicrobial resistance, particularly fluoroquinolone resistance. These strains include C. difficile ribotype (RT) 027, which originated in North America, and RT 017, which is most widespread in Asia. Despite being the most common cause of hospital-acquired infection in the developed world, and frequent misuse of antimicrobials in Asia, little is known about C. difficile in Asian countries. We aimed to determine the resistance profiles of a large collection of C. difficile isolates from Asia to an array of antimicrobials.
C. difficile isolates (n=414) from a 2014 study of 13 Asia-Pacific countries were tested for susceptibility to moxifloxacin, amoxicillin-clavulanate, erythromycin, clindamycin, rifaximin, metronidazole, vancomycin and fidaxomicin by the agar dilution method according to the Clinical & Laboratory Standards Institute and EUCAST guidelines. The most common strains among the collection were RTs 017 (n=68), 014/020 (n=45), 018 (n=41), 002 (n=38), 012 (n=20) and newly emerging strains QX 239 (n=15) and RT 369 (n=17).
All isolates were susceptible to metronidazole, vancomycin, amoxicillin-clavulanate and fidaxomicin. Moxifloxacin resistance was detected in all countries except Australia, in all RT 369 and QX 239 (MIC50=16mg/L and 32mg/L respectively) strains, 92.7% of RT 018 (MIC50=32mg/L) and 70.6% of RT 017 (MIC50=32mg/L) strains. All RT 012, 369 and QX 239 strains were also resistant to erythromycin (MIC50= >256mg/L) and clindamycin (MIC50= >32mg/L). Rifaximin resistance was common in RT 017 strains only (63.2%, MIC50=>32mg/L) and was not detected in Australian, Japanese or Singaporean isolates.
Antimicrobial susceptibility of C. difficile varies highly by strain type and by country across Asia. Emerging RTs 369 and QX 239 show high rates of resistance and high MICs, and the most common strain in Asia, RT 017, is highly resistant to many antimicrobials. Ongoing surveillance is clearly warranted.