Emergence of a clinical carbapenem-resistant Escherichia coli co-harboring blandm-5 and mcr-1.1 on the same plasmid.

OBJECTIVES

Escherichia coli is a major pathogen, and the emergence of carbapenem-resistant E. coli (CREC) significantly restricts clinical treatment options. Polymyxins are considered the last-line treatment for CREC infections; however, the occurrence of polymyxin-resistant CREC, particularly following reports of plasmid-mediated colistin resistance (mcr), poses an increasing challenge.

METHODS

In this study, we identified a polymyxin-resistant CREC strain isolated from the rectal swab of a patient hospitalized in a hematology ward. Antimicrobial susceptibility testings, S1-PFGE, Southern blot analysis, Conjugation Experiment, whole genome sequencing (WGS) and bioinformatic analysis were used to characterize the strain.

RESULTS

The strain showed resistance to all tested antimicrobial agents except tigecycline. By bioinformatic analysis, the strain was found to carry one copy of the mcr-1.1 gene and two copies of blaNDM-5 genes. One blaNDM-5 and the mcr-1.1 gene were co-located on a plasmid (pCDE2901_MCR-NDM), while the second blaNDM-5 gene resided on another plasmid (pCDE2901_NDM). The blaNDM-5 gene in pCDE2901_MCR-NDM was likely mobilized from pCDE2901_NDM via a transposon. The plasmid pCDE2901_NDM could successfully transferred from the donor strain CDE2901 to the recipient strain EC600, while the plasmid pCDE2901_MCR-NDM was unable to undergo horizontal transfer despite harboring mobile-associated genes.

CONCLUSIONS

Given the critical role of polymyxins in treating CREC infections, the co-transfer of polymyxin and carbapenem resistance may severely undermine the efficacy of clinical therapies. Strengthened surveillance and monitoring are imperative to curtail the spread of extensively drug-resistant (XDR) pathogens.