Temporal Trends and Associations of Antimicrobial Use and Resistance in Enterococcus Species From Broiler Farms in Canada

INTRODUCTION: Antimicrobials are widely used in animal production for the treatment, prevention, and control of infectious diseases. However, antimicrobial use (AMU) is also a key driver of antimicrobial resistance (AMR). In response, the Canadian poultry sector implemented a phased three-step AMU reduction strategy to mitigate the emergence and spread of AMR. Enterococci are ubiquitous inhabitants of the gastrointestinal tract of animals and serve as important sentinel organisms for AMR surveillance because of their capacity to acquire AMR. METHODS: This study investigated associations between farm management practices, including AMU, and AMR in enterococci isolated from broiler chickens. Farm management data were collected using standardized questionnaires, and faecal samples were obtained during farm visits. Phenotypic AMR profiles were determined by minimum inhibitory concentration testing of 623 isolates from 419 flocks across five Canadian provinces over a 4-year period. Generalized linear mixed models were used to evaluate associations between AMR and other factors, including AMU, province, year, breed, stocking density, downtime between flocks, and sanitation practices. RESULTS: Avilamycin use was significantly associated with avilamycin resistance in both E. faecalis and E. faecium. Provincial and temporal differences in resistance were observed for certain antimicrobials, with a notable decline in resistant isolates to Veterinary Drugs Directorate's Category II and III antimicrobials following implementation of the three-step AMU reduction strategy. CONCLUSIONS: These findings suggest that targeted AMU reduction strategies were associated with reducing AMR percentages in enterococci from Canadian broilers.