Antimicrobial resistance in bacteria isolated from horses from the Atlantic Provinces, Canada (1994 to 2013).

This study determined the antimicrobial susceptibility patterns and trends for selected bacteria isolated from horses using diagnostic data from the Atlantic Veterinary College Diagnostic Services Bacteriology Laboratory, Charlottetown, Prince Edward Island over a 20-year period. Streptococcus equi subsp. zooepidemicus and Escherichia coli were the most commonly isolated bacteria over the study period. Clinical samples were most frequently submitted from respiratory and reproductive systems. Most bacterial isolates were susceptible to ceftiofur. Resistance was most common in Gram-negative enteric bacteria, while streptococci were frequently susceptible to most of the antimicrobials tested including penicillin and trimethoprim-sulfamethoxazole. The antimicrobial resistance trends over the study period were relatively stable. Multi-drug resistance was observed in 9% of the bacterial isolates. Information provided in this study could be used to help guide rational, empirical antimicrobial treatment selection in equine practices in Atlantic Canada.