Heterogeneous Genetic Location of mcr-1 in Colistin-Resistant Escherichia coli Isolated from Humans and Retail Chicken Meat in Switzerland: Emergence of mcr-1-Carrying IncK2 Plasmids

We characterized the genetic environment of mcr-1 in colistin-resistant Escherichia coli strains isolated in Switzerland during 2014-2016 from humans (n=3) and chicken meat (n=6). Whole genome and plasmid sequencing identified mcr-1 integrated in IncX4 (of which, one carrying the mcr-1.2 variant), IncI2, IncHI2 and novel IncK2 plasmids (overall, n=7), as well as in the bacterial chromosome (n=2) in single or duplicate copies. Our study supports the easy mobilization of mcr-1 across diverse genetic locations.