Characterization of a Clinical Enterobacter hormaechei Strain Belonging to Epidemic Clone ST418 Co-carrying blaNDM-1, blaIMP-4 and mcr-9.1

An Enterobacter hormaechei isolate (ECL-90) simultaneously harboring blaNDM-1, blaIMP-4 and mcr-9.1 was recovered from the secretion specimen of a 24-year-old male patient in a tertiary hospital in China. The whole genome sequencing of this isolate was complete, and 4 circular plasmids with variable sizes were detected. Multi-locus sequence typing (MLST) analysis assigned the isolate to ST418, known as a carbapenemase-producing epidemic clone in China. blaIMP-4 and mcr-9.1 genes were co-carried on an IncHI2/2A plasmid (pECL-90-2) and blaNDM-1 was harbored by an IncX3 plasmid (pECL-90-3). The genetic context of mcr-9.1 was identified as a prevalent structure, “rcnR-rcnA-pcoE-pcoS-IS903-mcr-9-wbuC”, which is a relatively unitary model involved in the mobilization of mcr-9. Meanwhile, blaNDM-1 gene was detected within a globally widespread structure known as NDM-GE-U.S (“ISAba125–blaNDM-1–blaMBL”). Our study warrants that the convergence of genes mediating resistance to last-resort antibiotics in epidemic clones would largely facilitate their widespread in clinical settings, thus representing a potential challenge to clinical treatment and public health.