Longitudinal evaluation of interventions on antimicrobial use and antimicrobial resistance on broiler farms in West Java, Indonesia

To address the growing public health concern of antimicrobial resistance (AMR), this study evaluated the impact of a combination of targeted interventions on antimicrobial use (AMU) and AMR in commensal Escherichia coli within small- and medium-scale broiler farms in West Java, Indonesia. This longitudinal study was conducted from 2019 to 2023 and included data from 98 production cycles (across 19 farms) pre-intervention and 55 production cycles (across 14 farms) post-intervention. AMU was assessed using count-based treatment frequency per standardized 30-day cycle. Changes in AMU and AMR were analyzed using a hierarchical Bayesian negative-binomial regression and Bayesian Gaussian linear model, respectively, and included potential risk factors for AMU including mortality rates, biosecurity levels and seasonality. Fluoroquinolones were the most frequently used antimicrobials pre- and post-intervention. The observed total AMU (aggregated across all classes) decreased from 0.4 to a treatment frequency of 0.3, corresponding to a reduction from an average of 11 to 9 treatment days per cycle. Although the model did not indicate a significant effect of the intervention on overall AMU, a significant decline of 92.6 % in colistin use was observed, most likely attributable to a national ban on colistin use implemented in the study period. The proportion of E. coli isolates exhibiting non-wild-type phenotypes-defined as those with minimum inhibitory concentration (MIC) values above the epidemiological cutoff (ECOFF), indicating a deviation from the wild-type population-did not decline post-intervention across all 14 tested antimicrobials. The AMR model did not demonstrate a clear effect of the included risk factors but suggested a potential increase in resistance associated with higher levels of AMU. This study provides a comprehensive longitudinal assessment of AMU and AMR in small- and medium-scale broiler farms in West Java. The outcomes provide valuable baseline AMU and AMR levels and underscore the potential, and complexity, of targeted interventions to reduce AMU and mitigate AMR, and the need for further investigation into the effectiveness of AMU reduction strategies.