Passive surveillance of antimicrobial resistance in Salmonella and Escherichia coli isolates from Ontario livestock, 2007-2015.

Clinical isolates are important to antimicrobial resistance surveillance efforts because clinically ill animals are the direct targets of antimicrobial treatments. Thus, clinical data may provide a surveillance tool for identifying emerging resistance threats. The purpose of this study was to describe resistance trends in Escherichia coli and Salmonella spp. from clinically ill animals over time and evaluate the utility of these laboratory data as a passive surveillance tool. Susceptibility results of isolates from chickens, swine, and cattle recovered between 2007 and 2015 at a major veterinary diagnostic laboratory in Ontario, Canada were analyzed. Relative to other antimicrobials tested, visible trends highlighted high resistance to ampicillin and tetracycline in chicken E. coli, consistently high resistance to tetracycline, sulfisoxazole, and ampicillin among swine isolates, and an increase in cattle E. coli resistant to ampicillin and cephalothin over time. While the data show potential for use in surveillance, there are limitations of such a clinical dataset for predicting overall trends and guiding empirical treatment decisions.