Genomic features of an Escherichia coli ST156 strain harboring chromosome-located mcr-1 and plasmid-mediated blaNDM-5.

Abstract

The emergence of Escherichia coli strains coharboring the blaNDM and mcr genes has become a new challenge in clinical therapy because of their resistance to most antibiotics. This study reports the emergence of an E. coli strain GZEC065 isolated from blood sample of a patient in China with both chromosome-located mcr-1 and plasmid-mediated blaNDM-5 genes. Antimicrobial susceptibility testing showed that GZEC065 was resistant to most tested antimicrobials, including imipenem and polymyxin B. S1-nuclease-pulsed-field gel electrophoresis, Southern blotting analysis and conjugation assay was performed to determine the location and conjugative ability of mcr-1 and blaNDM-5 genes. Whole genome sequencing and analysis showed that GZEC065 belonged to sequence type ST156 and contained three different plasmids (46kb, 88kb and 142kb) with multiple resistance genes, such as mcr-1, blaNDM-5 and blaTEM-1. The blaNDM-5 gene was carried by the 46kb conjugative IncX3 plasmid, which has been reported frequently in China. The mcr-1 gene was located on the chromosome mediated by the Tn6330 mobile element and showed genetic complexity among different strains. The emergence of E. coli strains coharboring both chromosome-located mcr-1 and plasmid-mediated blaNDM-5 genes highlights the urgent need for alternative antibiotic treatment and continuous active surveillance.