Prevalence and risk factors of mcr-1-positive volunteers after colistin banning as animal growth promoter in China: a community-based case-control study.

Abstract

OBJECTIVES\nChina banned the use of colistin as animal growth promoter in April 2017. Herein, we report the prevalence of mcr-1 in the intestine of healthy human and risk factors associated with mcr-1 carriage after the implementation of the ban.\n\n\nMETHODS\nWe recruited 719 healthy volunteers from Shenzhen city from 1st March 2018 to 31st December 2019 to investigate the prevalence of mcr-1 in human intestine, and undertook a case-control study to ascertain the risk factors associated with mcr-1-positive population. Further comparative study was conducted to identify differences between genetic characteristics of mcr-1-positive and -negative Escherichia coli.\n\n\nRESULTS\nOverall, 56 (7·8%, CI: 5·9-10·0, n = 719) individual fecal samples were positive for mcr-1, and prevalence of mcr-1 among individuals in 2019 (2·4%, CI: 8·7-15·0, 7/294) was significantly lower than that in 2018 (11·5%, CI: 1·0-4·8, 49/425) (P < 0·0001). After the colistin banning, animal-derived food (pork and chicken meat) was no longer a risk factor for mcr-1 carriage in human intestine, whilst a higher intake of aquatic food (>75 g/day) and whole grains (>150 g/day) were associated with higher and lower risk of mcr-1 carriage, respectively (OR = 2·175, 95% CI: 1·047-4·517; OR = 0·045, 95% CI: 0·004-0·567). Comparing with mcr-1-negative E. coli, the mcr-1-positive E. coli had different patterns of resistance genes and genetic heterogeneity.\n\n\nCONCLUSIONS\nOur study implicate aquatic food is associated with mcr-1 carriage in healthy population, even after the ban on colistin. Dietary modification (eg. whole grains) may help combat mcr-1-positive bacterial colonization in the gut.