Changes in colistin resistance and mcr-1 abundance in Escherichia coli of animal and human origins following the ban of colistin-positive additives in China: an epidemiological comparative study.

BackgroundFollowing the discovery and emergence of the plasmid-mediated colistin resistance gene, mcr-1, the Chinese government formally banned colistin as an animal growth promoter on April 30, 2017. Herein, we report patterns in colistin resistance and mcr-1 abundance in Escherichia coli from animals and humans between 2015 and 2019, to evaluate the effects of the colistin withdrawal.MethodsWe did an epidemiology comparative study to investigate: annual production and sales of colistin in agriculture across mainland China according to data from the China Veterinary Drug Association from 2015 to 2018; the prevalence of colistin-resistant E coli (CREC) in pigs and chickens in 23 Chinese provinces and municipalities as reported in the China Surveillance on Antimicrobial Resistance of Animal Origin database from Jan 1, 2015, to Dec 31, 2016, and Jan 1, 2017, to Dec 31, 2018; the presence of residual colistin and mcr-1 in faeces from 118 animal farms (60 pig, 29 chicken, and 29 cattle) across four provinces over July 1, 2017, to August 31, 2017, and July 1, 2018 to August 31, 2018; the prevalence of mcr-1-positive E coli (MCRPEC) carriage in healthy individuals attending routine hospital examinations across 24 provinces and municipalities from June 1 to July 30, 2019, comparing with equivalent 2016 data (June 1 to September 30) from our previous study in the same hospitals; and the patterns in CREC prevalence among hospital E coli infections across 26 provinces and municipalities from Jan 1, 2015, to Dec 31, 2016, and Jan 1, 2018, to Dec 31, 2019, reported on the China Antimicrobial Surveillance Network.FindingsAfter the ban on colistin as a growth promoter, marked reductions were observed in the production (27 170 tonnes in 2015 vs 2497 tonnes in 2018) and sale (US$71·5 million in 2015 vs US$8·0 million in 2018) of colistin sulfate premix. Across 118 farms in four provinces, mean colistin residue concentration was 191·1 μg/kg (SD 934·1) in 2017 versus 7·5 μg/kg (50·0) in 2018 (p