Antimicrobial use and bacterial resistance in broilers
Study results for Salmonella, Campylobacter, E. coli and Enterococcus
4 November 2024
2 minute read
By: Editor's note: the following is from a poster presentation by Randall Singer, DVM, PhD, and colleagues, University of Minnesota, during the 2024 annual conference of the American Association of Avian Pathologists.
The objective of this project was to design a sustainable on-farm antimicrobial use and antimicrobial resistance monitoring program representative of the US broiler chicken industry. The program was implemented as a cross-sectional sampling of farms. Each company that voluntarily participated selected the complexes to enroll, and then each complex selected 4-8 farms for sampling during each 3-month interval.
Litter samples were cultured for Salmonella, Campylobacter, E. coli and Enterococcus. A total of 346, 356, 364 and 357 farms were sampled in 2020, 2021, 2022 and 2023, respectively. Approximately 50% of the sampled farms raised animals without antimicrobials. No medically important antimicrobials were used in the feed of the sampled flocks.
S. Kentucky and S. Infantis were the most common Salmonella serotypes identified. Most S. Kentucky isolates were pan-susceptible or resistant to tetracycline whereas most S. Infantis isolates were multidrug resistant, typically with resistance to sulfonamide, tetracycline and fluoroquinolone antimicrobials. There was no statistical association between antimicrobial use and the presence of multidrug resistant S. Infantis.
Most Campylobacter isolates were C. jejuni, and most were pan-susceptible or resistant to tetracycline only; approximately one-third had resistance to ciprofloxacin. There was no statistical association between antimicrobial use and resistance in C. jejuni isolates.
The most common antimicrobial resistance in E. coli was against sulfonamides and tetracyclines, but there was no statistical association between antimicrobial use and antimicrobial resistance in E. coli. The prevalence of resistance against gentamicin in E. coli was between 10 and 20%, which represents a substantial decline from the prevalence 5 to 10 years ago.
The most common antimicrobial resistance in Enterococcus was against streptogramins and tetracyclines, with some resistance to erythromycin and ciprofloxacin, especially in E. faecium. To capture long-term associations between antimicrobial use and antimicrobial resistance, these datasets need to be collected in parallel at the farm level.
