The resistance of mcr-1-carrying Enterobacteriaceae to polymyxin, the last resort antibiotic, has raised great concern worldwide. In this study, four mcr-1-carrying plasmids isolated from Klebsiella pneumoniae clinical isolates were completely sequenced and genome compositions of the mcr-1-carrying plasmids were analyzed.
The antimicrobial resistance genes and susceptibility of four mcr-1-carrying K. pneumoniae isolates were characterized. The comparison of mcr-1-carrying plasmids with closely related plasmids and analysis of mcr-1 gene cassette were carried out.
Genome compositions of four mcr-1-carrying plasmids revealed the Tn6330 and Tn6390 cassettes embedded in two IncHI1 type plasmids, ΔTn6330 in an IncHI2 type plasmid and mcr-1-pap2 in an IncX4 type plasmid. We also predicted the intermediate structures of the Tn6330 and Tn6390 cassettes.
The dissemination of the colistin-resistant gene mcr-1 in Taiwan could have been driven by various plasmids and mobile gene cassettes. The evolution of the genetic environment has led to diversity in the mcr-1 gene among plasmids. This work sheds light on the urgent need for continued surveillance of the worldwide distribution of mcr-1 and evaluates public health risks for colistin resistance.