Assessing the associations between antimicrobial use and antimicrobial susceptibility testing results in Clostridium perfringens in Canadian broiler chickens, turkeys, and layer chickens from 2018 to 2023

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OBJECTIVE: The objective of this study was to characterize the antimicrobial susceptibility of Clostridium perfringens isolates recovered from healthy broiler chicken, turkey, and layer flocks in Canada, and to assess potential associations between observed antimicrobial susceptibility test (AST) results and reported antimicrobial use (AMU). METHODS: AMU data from questionnaires, and fecal samples for AST, were collected by 17 poultry veterinarians across Canada. Data from 210 broiler chicken, 91 turkey, and 66 layer chicken flocks from 2017 to 2018 (broilers only), 2021, and 2023 were analyzed. Minimum inhibitory concentration (MIC) results were categorized as high or low based on available clinical breakpoints. Based on levels of AMU and distributions of MIC data, mixed-effect logistic regression models were built to examine the relationship between bacitracin use and high MICs in broilers and turkeys. RESULTS: Bacitracin was the most commonly reported antimicrobial used across all three poultry commodities studied. Significant differences in MIC distributions for bacitracin were observed among the three commodities, with broilers demonstrating the highest percentage of isolates in the upper measurable MIC range. Logistic regression analysis revealed a significant relationship (P-value ≤0.05) between bacitracin use and MIC values. Specifically, each incremental increase of 1 mg/kg in bacitracin use raised the odds of detecting a high MIC value by 4.5 % in broilers (OR = 1.045) and 9.6 % in turkeys (OR = 1.096). CONCLUSIONS: These findings suggest that elevated AMU, particularly bacitracin, is associated with reduced susceptibility (higher MICs) in C. perfringens isolates from poultry, highlighting that prudent use of antimicrobials is needed to preserve antimicrobial efficacy.

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