Colocation of the Polymyxin Resistance Gene mcr-1 and a Variant of mcr-3 on a Plasmid in an Escherichia coli Isolate from a Chicken Farm.

A colistin-resistant Escherichia coli isolate from a commercial poultry farm in China carried two colistin resistance genes, mcr-1 and variant of mcr-3 , in an IncP plasmid. The variant of the mcr-3 gene, named mcr-3.11 , encoded two amino acid substitutions compared with the mcr-3 gene. A novel genetic structure, IS Kpn40-mcr-3-dgkA -IS Kpn40 , might be the key element mediating the translocation of mcr-3 through the formation of a circular form. The mcr-1 and mcr-3 genes, which are colocated on a plasmid, might pose a huge threat to public health.