Emergence of a clinical isolate of E. coil ST297 co-carrying bla_NDM-13 and mcr-1.1 in China

The coexistence of carbapenem resistance genes and mcr-1.1 in Enterobacterales has been an urgent and persistent threat to global public health. In this study, we isolated a clinical NB4833, an Escherichia coli isolate that co-carries mcr-1.1 and bla_NDM-13.

This study aimed to isolate a clinical NB4833, an Escherichia coli isolate that co-carries mcr-1.1 and bla_NDM-13 and investigated the phenotypic and genotypic characteristics of plasmids harbored by E. coli isolate NB4833.

Antimicrobial susceptibility testing and conjugation assay were performed on E. coli isolate NB4833. Stability of the plasmid and growth rate determination were used to characterize the plasmids harboring mcr-1.1 and bla_NDM-13. In addition, the genetic characteristics of the plasmids were analyzed based on whole-genome sequencing of the strain and comparative genetic analysis with related plasmids.

Whole-genome sequencing showed that the isolate carried multiple resistance genes and possessed phenotypes indicative of all antibiotic resistance except tigecycline. And the mcr-1.1- and bla_NDM-13-harbouring plasmids showed relatively high similarity to the related plasmids. The pNB4833-NDM-13 plasmid was capable of trans conjugation with an efficiency of 1.04 × 10^-2 in a filter mating experiment and the transconjugant J53/ pNB4833-NDM-13 was able to be stably inherited after 10 days of passage.

To our knowledge, this is the first report of the coexistence of the IncI2 plasmid carrying mcr-1.1 and a bla_NDM-13-carrying integrated IncFIB/IncFII plasmid in an ST297 clinical E. coli isolate. In addition, we investigated a novel plasmid carrying bla_NDM-13. Our study expands the diversity of plasmids carrying bla_NDM-13, which exhibits epidemic importance in bacterial resistance. Therefore, there are important measures that should be taken to prevent the spread of these plasmids.