Comprehensive resistome analysis reveals the prevalence of NDM and MCR-1 in Chinese poultry production

Abstract

By 2030, the global population will be 8.5 billion, placing pressure on international poultry production, of which China is a key producer¹. From April 2017, China will implement the withdrawal of colistin as a growth promoter, removing over 8,000 tonnes per year from the Chinese farming sector². To understand the impact of banning colistin and the epidemiology of multi-drug-resistant (MDR) Escherichia coli (using bla_NDM and mcr-1 as marker genes), we sampled poultry, dogs, sewage, wild birds and flies. Here, we show that mcr-1, but not bla_NDM, is prevalent in hatcheries, but bla_NDM quickly contaminates flocks through dogs, flies and wild birds. We also screened samples directly for resistance genes to understand the true breadth and depth of the environmental and animal resistome. Direct sample testing for bla_NDM and mcr-1 in hatcheries, commercial farms, a slaughterhouse and supermarkets revealed considerably higher levels of positive samples than the bla_NDM- and mcr-1-positive E. coli, indicating a substantial segment of unseen resistome-a phenomenon we have termed the 'phantom resistome'. Whole-genome sequencing identified common bla_NDM-positive E. coli shared among farms, flies, dogs and farmers, providing direct evidence of carbapenem-resistant E. coli transmission and environmental contamination.