Date Published: February 26, 2019
Publisher: Public Library of Science
Author(s): Li-Juan Zhang, Ling Yang, Xi-Xi Gu, Pin-Xian Chen, Jia-Li Fu, Hong-Xia Jiang, Pradeep Dudeja.
We investigated the molecular characteristics and antimicrobial susceptibility of Clostridium difficile isolated from animals in China. We obtained 538 rectal swabs from pigs, chickens and ducks in 5 provinces during 2015 and 2016. C. difficile isolates were characterized by detection of toxin genes, multilocus sequence typing and ribotyping. And antimicrobial susceptibility testing was performed using the agar dilution method. Out of 538 samples, 44 (8.2%) were C. difficile positive with high prevalence in pigs (n = 31). Among these, 39 (88.6%) were toxigenic including 14 (31.8%) that were A+B+CDT+ and 13 (29.5%) A+B+. The remaining 12 (27.3%) were A-B+. We identified 7 ST types and 6 PCR ribotypes. The most predominant type was ST11/RT078 with toxin profile A+B+CDT+ and all were isolated from piglets with diarrhea. ST109 isolates possessed two different toxigenic profiles (A-B-CDT- and A-B+CDT-) and although it was not the most prevalent sequence type, but it was widely distributed between chickens, ducks and pigs in the 5 provinces. All C. difficile isolates were fully susceptible to vancomycin, metronidazole, fidaxomicin, amoxicillin/clavulanate and meropenem but retained resistance to 4 or 5 of the remaining antibiotics, especially cefotaxime, tetracycline, ciprofloxacin, cefoxitin. The RT078/ST11 isolates were simultaneously resistant to cefotaxime, tetracycline, cefoxitin, ciprofloxacin and imipenem. This is the first report of the molecular epidemiology of C. difficile isolated from food animals in China. We identified the epidemic strain RT078/ST11 as the predominate isolate among the animals we screened in our study.
Clostridium difficile is a strictly anaerobic, spore-forming Gram-positive bacterium that colonizes the gastrointestinal tract of humans and animals and cause disease . C. difficile pathogenesis is associated with the production of two enterotoxins (A and B) encoded by tcdA and tcdB on its pathogenicity locus. Some strains also produce a third toxin called binary toxin (cytolethal distending toxin, CDT) that is associated with increased disease severity and 30-day mortality .
In the present study, we isolated 31 C. difficile strains from pigs at a rate of 7.8%, which was significantly lower than previously reported rates of 36% ~ 50% [34, 35]. This difference can be accounted for by the animal ages since the prevalence of C. difficile in pigs decreases with age . Our study samples were derived from nursery pigs and sows with only a few samples from piglets. Interestingly, strain RT078 (GZ2/ST11) predominated and these samples were all obtained from piglets. In addition, we found 9 C. difficile in chickens and 4 C. difficile strains from ducks with isolate rates at 7.4% (9/121) and 21% (4/19) respectively. Since China is the largest producer of chickens and ducks for food, the isolation of C. difficile from these animals indicates a potential public health threat.
The present study is the first report of hypervirulent strain RT078/ST11 strain from piglets in China. This strain was multiply resistant to CXT/TET/CIP/CTX/IPM. Our results indicated that ST109 was the most widely distributed type of C. difficile from food animals in China. These ST isolates were obtained from different animals and provinces and possessed different resistance phenotypes. This study provides an important baseline for ongoing long-term surveillance of antimicrobial resistance and prospective tracking of prominent and emerging strain types in China.