Background: We aimed to investigate the prevalence, molecular epidemiology and risk factors for Extended Spectrum beta-Lactamase-producing Enterobacteriaceae (ESBL-E) shedding by race horses. A cross-sectional study was performed involving fecal samples collected from 169 Thoroughbred horses that were housed at a large racing facility in Ontario, Canada. Samples were enriched, plated on selective plates, sub-cultured to obtain pure cultures and ESBL production was confirmed. Bacterial species were identified and antibiotic susceptibility profiles were assessed. E. coli sequence types (ST) were determined using multi locus sequence type (MLST) analysis. Medical records were reviewed and assessment of risk for individual variables was performed.
Results: Adult horses (n=169), originating from 16 different barns, were sampled. ESBL-E shedding rate was 12% (n=21/169, 95% CI 8-18%); 22 isolates ESBL-E were molecularly studied (one horse had two isolates). The main species was E. coli (91%) and the major ESBL gene was CTX-M-1 (54.5%). Nine different E. coli ST were identified. Three new E. coli sequence types were identified. Sixty-four percent of total isolates were defined as multi-drug resistant. ESBL-E shedding horses originated from 8/16 different barns; whereas 48% (10/21) of them originated from one specific barn. Overall, antibiotic treatment in the previous month was found as a risk factor for ESBL-E shedding (p= 0.013, OR=41, 95% CI 2-762).
Conclusions: Our findings demonstrate the potential diverse reservoir of ESBL-E in Thoroughbred race horses. Multi-drug resistant bacteria should be further investigated to improve antibiotic treatment regimens and equine welfare. Less...