Investigation of antimicrobial resistance in Salmonella, Escherichia coli and Campylobacter isolated from Ontario sheep flocks

This thesis examines the prevalence of antimicrobial resistance (AMR) in enteric bacteria isolated from Ontario sheep flocks, and associations between antimicrobial use (AMU) and AMR. All AMU information from 49 flocks over a 12 month period was recorded. Pooled fecal samples from initial and final visits were cultured for enteric bacteria. Isolates were tested for antimicrobial susceptibility. The prevalence of resistance was infrequent in Salmonella (0%) and E. coli (13.1%), but relatively more common in Campylobacter (45.7%). Logistic regression was used to model potential AMU (quantitative and qualitative) risk factors for tetracycline resistance in generic E. coli and Campylobacter. Risk factors in the E. coli model included the use of injectable sulfonamides or trimethoprim-sulfonamide combinations and the use of tetracycline in the feed or water. No associations were identified for Campylobacter resistance outcome variables. Although the prevalence of AMR in participating flocks was low, risk factors for resistance were identified.