Objectives: A plasmid-mediated colistin resistance gene, mcr-1 , has been reported worldwide and has caused concern regarding a major therapeutic challenge. Alarmingly, mcr-1  has spread into clinical carbapenem-resistant Enterobacteriaceae isolates, resulting in extensively drug-resistant and even pan drug-resistant isolates that can cause untreatable infections. In this study, we report isolation of an extensively drug-resistant Escherichia coli  strain EC1188 that coproduces NDM-16 and MCR-1 from a urine sample taken from a patient with craniocerebral injury.
Materials and methods: E. coli  strain EC1188 was identified and subjected to genotyping, susceptibility testing and conjugation experiments. The genetic locations of bla _NDM-16 and mcr-1  were established with southern blot hybridization. The complete genome sequence of this strain was obtained and the genetic characteristics of the mcr-1 - and bla _NDM-16-harboring plasmids were analyzed. In addition, comparative genetic analyses of mcr-1  and bla _NDM-16 with closely related plasmids were also carried out.
Results: Whole-genome sequencing revealed that strain EC1188 possess various resistance genes and virulence genes. S1-pulsed-field gel electrophoresis and southern blot suggested that the bla _NDM-16 and mcr-1  genes were located on an ~65 kb plasmid and an ~80 kb plasmid, respectively. Moreover, the two genes could successfully transfer their resistance phenotype to E. coli  strain C600. Sequence analysis showed that these two plasmids possessed high sequence similarity to previously reported bla _NDM-5-harboring and mcr-1 -harboring plasmids in China.
Conclusion: To the best of our knowledge, this is the first report to isolate an E. coli  strain that coproduces NDM-16 and MCR-1. In addition, we characterized the bla _NDM-16-harboring plasmid for the first time. Our study further emphasizes that the co-occurrence of the two prevalent transferrable resistance plasmids in a single isolate is highly significant because infections caused by MCR-1–producing carbapenem-resistant Enterobacteriaceae isolates are increasing each year. It is imperative to perform active surveillance to prevent further dissemination of MCR-1–producing CRE isolates.
Keywords: E. coli , mcr-1, NDM-16, CRE, colistin resistance, extensively drug-resistant bacteria