Decreasing antimicrobial resistance in representative UK livestock species was associated with reduced total sales of antimicrobials in the last decade.

Background: Antimicrobial resistance (AMR) in pathogenic bacteria is a leading global health crisis estimated to currently contribute to human mortality on a par with malaria or HIV, with potential to increase in importance. Livestock can comprise a reservoir of AMR, which can be directly or indirectly transmitted to humans and vice versa. Representative surveillance schemes for antimicrobial use (AMU) and AMR in livestock populations have been running in the UK since 2014, during which time veterinary AMU has decreased, providing an opportunity to assess and quantify the potential relationship between AMU and AMR.

Objectives: To analyse associations between the decrease of total sales of antimicrobials for livestock and the prevalence of non-wild type (WT) (AMR) Escherichia coli detected in UK pigs and poultry in 2 year weighted data points from 2014 to 2021.

Methods: AMR was measured with epidemiological cut-off values (ECOFFs). Associations between prevalence of AMR, multidrug resistance (non-WT phenotypes to three or more classes of antimicrobials), (indicator measures of AMR), and standardized veterinary antimicrobial sales were modelled by regression.

Results: The decrease in any detectable AMR phenotypes in E. coli (primary indicator) was associated with the decrease of total sales of antimicrobials from 59.27 mg/population correction unit (PCU) in 2014-15 to 29.14 in 2020-21 (OR: 2.69, P < 0.001). Furthermore, prevalence of E. coli displaying multidrug resistance (secondary indicator) was also associated with the decrease in sales of antimicrobials (OR: 2.58, P < 0.001).

Conclusions: The decrease in sales of antimicrobials in livestock was associated with a decrease in non-WT E. coli found in livestock.