Characterization of a novel bla(NDM-5)-harboring IncFII plasmid and an mcr-1-bearing IncI2 plasmid in a single Escherichia coli ST167 clinical isolate

BACKGROUND AND PURPOSE: The spread of the plasmid-mediated, colistin-resistance gene mcr-1 into New Delhi metallo-β-lactamase (NDM)-producing bacterial isolates can cause untreatable infections. In this study, we conducted a molecular characterization of a novel, conjugative, bla(NDM-5)-positive IncFII plasmid (pNDM-EC16-50) together with an mcr-1-bearing IncI2 plasmid in a single Escherichia coli ST167 clinical isolate EC16-50. METHODS AND RESULTS: EC16-50, which belongs to the E. coli strain ST167 and phylogroup A, was identified to co-produce NDM-5 and MCR-1. S1-PFGE and Southern blotting showed that bla(NDM-5) and mcr-1 genes were located oñ95 kb and ~65 kb plasmids, respectively. A conjugation assay revealed that both bla(NDM-5)- and mcr-1-bearing plasmids were self-transmissible. Comparative plasmid analysis suggested that bla(NDM-5)-harboring F2:A-:B-plasmid might have evolved from the well-reported NDM-carrying pMC-NDM-like plasmid via recombination with a locally emerged pSJ_94 plasmid, whereas the mcr-1-carrying IncI2 plasmid was similar to previously reported mcr-1-bearing plasmids in China. CONCLUSION AND IMPACT: This study represents the first report of the NDM-5 carrying Inc-FII- but not IncX3-type plasmid in an MCR-1-producing E. coli isolate. More striking was the dissemination of mcr-1 in a successful epidemic NDM-5-producing E. coli clone ST167, which could facilitate the spread of colistin resistance in carbapenemase-producing E. coli isolates.