Conjugal Transfer, Whole Genome Sequencing, and Plasmid Analysis of Four mcr-1 -bearing Isolates from U.S. Patients.

Four Enterobacteriaceae clinical isolates bearing mcr-1 gene-harboring plasmids were characterized. All isolates demonstrated the ability to transfer colistin resistance to E. coli; plasmids were stable in conjugants after multiple passages on non-selective media. mcr-1 was located on an IncX4 (n=3) or IncN (n=1) plasmid. The IncN plasmid harbored 13 additional antimicrobial resistance genes. Results indicate the mcr-1 -bearing plasmids in this study are highly transferable in vitro and stable in the recipients.