Flattening Patterns of Antimicrobial Resistance Levels in Indicator E. coli in Dutch Livestock.

INTRODUCTION: Antimicrobial resistance (AMR) is defined by the World Health Organization as one of the most important health threats, that needs a One Health approach. Monitoring AMR in livestock is an important element, which has been done in the Netherlands in a monitoring program since 1998. The aim was to analyse AMR trends during the periods 2010-2018 and 2019-2023. METHODS: A dataset containing the antimicrobial resistance data of > 12,000 indicator E. coli isolates collected from faecal samples from broilers, fattening pigs and veal calves at slaughter houses, as part of the Dutch AMR monitoring program, was built to analyze AMR trends. ECOFF values were used to distinguish wild-type (WT) and non-wild-type (non-WT, phenotypically resistant) isolates. RESULTS: In the period 2010-2018 decreasing resistance patterns to most antibiotics were seen in broilers, fattening pigs and veal calves. However, in the period 2019-2023 flattening resistance patterns were observed in broilers and fattening pigs for antibiotics amoxicillin/ampicillin, sulfamethoxazole and trimethoprim, at relatively high levels of resistance, despite a reduction in antibiotic usage during this period. CONCLUSIONS: Following a significant decreasing trend in the prevalence of AMR between 2010 and 2018, no significant changes in the prevalence of AMR were observed between 2019 and 2023 for most antibiotics. To get more insight into the limited correlation between usage and resistance in recent years, further studies are needed to analyse the relation, and underlying factors, between antibiotic usage and AMR more in depth.