The First Report of mcr-1-Carrying Escherichia coli, Isolated from a Clinical Sample in the North-East of Romania

Abstract

Colistin resistance poses a significant clinical challenge, particularly in Gram-negative bacteria. This study investigates the occurrence of plasmid-mediated colistin resistance among Enterobacterales isolates (Escherichia coli, Klebsiella pneumoniae, and Enterobacter spp.) and non-fermentative rods (Acinetobacter baumannii and Pseudomonas aeruginosa). We analyzed 114 colistin-resistant isolates that were selected, based on resistance phenotypes, and isolated between 2019 and 2023. To achieve this, we used the rapid immunochromatographic test, NG-Test^® MCR-1; multiplex PCR for mcr-1 to mcr-8, and real-time PCR for mcr-1 and mcr-2. One E. coli isolate was identified as carrying the mcr-1 gene, confirmed by NG-Test^® MCR-1, multiplex PCR and whole-genome sequencing. This strain, belonging to ST69, harbored four plasmids, harboring different antimicrobial resistance genes, with mcr-1 being located on a 33,304 bp circular IncX4 plasmid. No mcr-2 to mcr-8-positive isolates were detected, prompting further investigation into alternative colistin resistance mechanisms. This is the first report of a mcr-1-positive, colistin-resistant E. coli isolated from a human clinical sample in the North-East of Romania.

Keywords: E. coli; Enterobacterales; antimicrobial resistance; colistin resistance; mcr-1-mcr-8; whole-genome sequencing.

Figure 1

A schematic circular representation of the E. coli IncX4 plasmid.