Characterization of an ST38 carbapenem-resistant and highly virulent Escherichia coli carrying conjugatively transferable ColV virulence-resistance and bla_NDM-5-positive resistance plasmids

Objectives: To characterize an Escherichia coli strain causing bloodstream infection encoding both high-virulence and carbapenem-resistance phenotypes.Methods: Antimicrobial susceptibility testing, WGS and bioinformatics analysis were performed to characterize strain E1. The function of the ColV plasmid was investigated by the Galleria mellonella infection model, serum killing and macrophage killing assays. The fitness effect of the ColV plasmid was tested by growth curve, plasmid stability tests and the in vitro competition assay. The conjugation assay was performed to test the transferability of the ColV and bla(NDM-5)-carrying plasmids.Results: E. coli E1 from bloodstream infection was MDR and highly virulent in the G. mellonella infection model. It belonged to phylogroup D, ST38 and serotype O7:H8. E1 carried a conjugatively transferable IncI1-type bla(NDM-5)-positive plasmid, which conferred carbapenem resistance, a conjugative IncFIB/FII-type ColV plasmid encoding an array of virulence-associated genes and antibiotic resistance genes bla(TEM-1B), strAB and sul2, and seven other plasmids. Co-transfer of the ColV plasmid and the bla(NDM-5)-positive plasmid was observed. The ColV virulence-resistance hybrid plasmid contributed to the virulence, resistance to serum killing, and macrophage phagocytosis in E. coli E1. The carriage of this ColV plasmid did not constitute an in vitro fitness burden to strain E1 but caused fitness costs to E. coli strain EC600.Conclusions: The emergence of such a highly virulent and resistant strain with conjugative bla(NDM-5)-positive and ColV plasmids posed a significant threat to public health. Implementation of control measures is needed to prevent such strains from further disseminating in hospital settings and the community.