Surveillance of antimicrobial use and resistance is needed to manage antimicrobial resistance in bacteria. In this study, data were collected on antimicrobial use and resistance in Staphylococcus aureus (n=562), isolated from intramammary
infections and (sub)clinical
mastitis cases on 89 dairy farms in 4 regions of Canada [Alberta, Ontario, Québec, and the Maritime Provinces (Prince Edward Island, Nova Scotia, and New Brunswick)]. Dairy producers were asked to deposit empty drug containers into specially provided receptacles, and antimicrobial
drug use rate was calculated to quantify antimicrobial use. Minimum inhibitory concentrations were determined using the Sensititer
bovine mastitis plate system (TREK Diagnostic Systems Inc., Cleveland,
OH), containing antimicrobials commonly used for
mastitis treatment and control. Multivariable logistic regression models were built to determine herd-level risk factors of
penicillin,
ampicillin,
pirlimycin,
penicillin-
novobiocin combination,
tetracycline and
sulfadimethoxine resistance in Staph. aureus isolates. Intramammary administration of the
penicillin-
novobiocin combination for dry cow
therapy was associated with
penicillin and ampicillin resistance [odds ratio (OR): 2.17 and 3.10, respectively]. Systemic administration of
penicillin was associated with penicillin resistance (OR: 1.63). Intramammary administration of
pirlimycin for lactating cow
mastitis treatment was associated with
pirlimycin resistance as well (OR: 2.07). Average herd parity was associated with
ampicillin and tetracycline resistance (OR: 3.88 and 0.02, respectively). Average herd size was also associated with tetracycline resistance (OR: 1.02). Dairy herds in the Maritime region had higher odds of
penicillin and lower odds of ampicillin resistance than dairy herds in Québec (OR: 2.18 and 0.19, respectively). Alberta dairy herds had lower odds of
ampicillin and
sulfadimethoxine resistance than dairy herds in Québec (OR: 0.04 and 0.08, respectively). Ontario dairy herds had lower odds of
tetracycline and
sulfadimethoxine resistance than dairy herds in Québec (OR: 0.05 and 0.33, respectively). Herd-level use of certain antimicrobials administered for
mastitis treatment and control, such as intramammary
penicillin and
pirlimycin as well as systemically administered
penicillin and
florfenicol, was positively associated with antimicrobial resistance in
bovine mastitis pathogens in the field conditions. Differences in antimicrobial resistance outcomes across 4 regions of Canada were observed.