mcr-1 Enterobacteriaceae from human faeces in Guangzhou, China. Enterobacteriaceae bacterium

mcr-1-mediated colistin resistance in Enterobacteriaceae is of concern, given colistin is frequently used as a treatment of last resort in multi-drug resistant Enterobacteriaceae infections. This study investigated increases in mcr-1-harbouring and more recent increases in mcr-1-harbouring/third generation cephalosporin-resistant Enterobacteriaceae human gastrointestinal colonization rates (Guangzhou, 2011-2016) using whole genome sequencing of isolates cultured from faeces.In mcr-1/third generation cephalosporin-resistant isolates (predominantly Escherichia coli), we identified wide bacterial strain diversity, mcr-1 in association with common plasmid backbones, and frequent mcr-1 chromosomal integration. Significant sequence similarity with other published mcr-1 plasmid sequences was consistent with pig-chicken-human spread.The numerous genetic mechanisms associated with mcr-1 have likely contributed to its dissemination, and will facilitate its persistence; the high prevalence of mcr-1 in multi-drug resistant E. coli successfully colonising humans in Guangzhou is a clinical threat.