Genomic characterization of an ST44 Escherichia coli isolate harboring an mcr-8.2-bearing IncR plasmid from a paediatric patient in China.

OBJECTIVES

The emergence of plasmid-mediated mobile colistin resistance (mcr) genes poses a serious threat to the clinical efficacy of colistin, a last-resort antibiotic for multidrug-resistant gram-negative bacterial infections. The occurrence of the less prevalent mcr-8 variant in clinically relevant species remains poorly characterized. This study aimed to characterize an ST44 E. coli isolate harbouring an mcr-8.2-bearing IncR plasmid from a paediatric patient in China.

METHODS

A faecal E. coli isolate from a 5-year-old patient was analysed. Antimicrobial susceptibility was determined by broth microdilution, and conjugation assays were performed to assess plasmid transferability. Comparative genomic analysis was performed to identify multiple resistance determinants, virulence factors, and plasmid replicon types. A global phylogenetic analysis was conducted to contextualize the isolate among publicly available E. coli ST44 genomes.

RESULTS

The isolate belonged to ST44 and showed resistance to colistin (MIC = 8 mg/L). Genomic analysis revealed the presence of an IncR plasmid, designated p4717_mcr-8, harbouring mcr-8.2 along with additional resistance genes, including mph(A), aac(3)-IId, blaTEM, and rmtB. The plasmid was transferable to E. coli J53 at a frequency of 4.63 × 10-4. The mcr-8.2 gene was embedded within a conserved ISEcl1-mcr-8.2-ISKpn26 genetic structure. Phylogenetic analysis of publicly available ST44 genomes suggested that this lineage is not a common reservoir of mcr genes.

CONCLUSIONS

This study reports a mobile mcr-8.2-carrying plasmid in an ST44 E. coli isolate from a paediatric patient, highlighting a potentially under recognized reservoir for silent dissemination and emphasizing the need for active surveillance of mcr genes in paediatric populations.