Local temperature and humidity are associated with proportion of antimicrobial-resistant Escherichia coli isolates in farm environments: considerations for on-farm surveillance

Evidence suggests that increased local temperatures are associated with higher prevalence of antimicrobial resistance (AMR) in environmental bacteria. This observational cohort study investigates associations between local climate and the proportion of antimicrobial-resistant Escherichia coli isolated from 2,766 farm environment samples from 53 English dairy farms. A non-linear Bayesian model that accounts for decreased test sensitivity at low E. coli abundance was used to estimate the proportion of antimicrobial-resistant E. coli from colony count data. A 20°C increase in local temperature was associated with a 5.0-fold increase in the proportion of streptomycin-resistant E. coli (95% credible interval [CI]: 1.03–33.0; absolute increase: 0.2%, 95% CI: 2.3 × 10 ⁻³ %–1.2%). Weaker evidence suggested that increased temperatures were associated with increased proportions of tetracycline-resistant E. coli . Increasing relative humidity was associated with an increase in the proportion of amoxicillin-, streptomycin-, and tetracycline-resistant E. coli . A 32% increase in relative humidity (from 60% to 92%) was associated with a 4.7-fold increase in the proportion of amoxicillin-resistant E. coli (median; 95% CI: 1.4–15.7; absolute increase: 1.3%, 95% CI: 0.2%–3.5%). For amoxicillin and streptomycin, a synergistic effect where increasing both temperature and humidity was associated with increased proportions of antimicrobial-resistant E. coli was observed, with weak evidence of this effect observed for tetracycline. These findings highlight the importance of considering weather conditions, sample characteristics, and seasonality in livestock AMR surveillance. Associations between local weather conditions and the proportion of livestock E. coli exhibiting AMR suggest that climate change may influence the burden of One Health AMR.