Ban of colistin livestock feed supplementation decreased the prevalence of colistin-resistant Escherichia coli in Ecuador

Objectives: In 2019, Ecuador implemented a ban on colistin feed supplementation owing to the increasing prevalence of colistin-resistant bacteria; however, the impact of this ban remains unclear. Methods: In this study, we aimed to elucidate the effects of the 2019 colistin ban by comparing the prevalence of colistin-resistant Escherichia coli in Ecuador with that in Vietnam, where colistin use is still permitted. We isolated colistin-resistant E. coli from the fecal samples of residents and detected mobile colistin resistance (mcr) genes in both the fecal samples and isolates. Results: Prevalence of colistin-resistant E. coli significantly decreased from 80.6 % in 2019 (n = 139) to 4.7 % in 2022 (n = 106) in Ecuador. Meanwhile, colistin-resistant E. coli prevalence only decreased from 84.7 % in 2017 (n = 98) to 62 % in 2024 (n = 50) in Vietnam. Notably, 96.8 % of the colistin-resistant E. coli isolates in Vietnam carried the mcr genes in 2024, whereas only 4.7 % of the isolates in Ecuadorian fecal samples harbored these genes in 2023. Conclusions: Overall, our findings highlight the significant impact of colistin use regulations on the decreased prevalence of colistin-resistant E. coli among Ecuadorian residents.