Emergence and diversity of IncHI2 plasmids co-carrying carbapenemase genes and mcr-9.1/9.2 in Enterobacter hormaechei from a Chinese children's hospital.

OBJECTIVE

This study aimed to characterize the IncHI2 plasmids co-harbouring carbapenemase genes and mcr-9 genes in carbapenem-resistant Enterobacter hormaechei (CREH) isolated from a children's hospital in Suzhou, China.

METHODS

Whole-genome sequencing (WGS) was employed to determine the genome sequences of 12 non-duplicate CREH strains. The molecular features of CREH strains and IncHI2 plasmids harbouring carbapenemase genes with or without mcr-9 genes were characterized through genomic analysis. Conjugal transfer assay and plasmid stability testing were used to evaluate the transfer ability and stability of IncHI2 plasmids.

RESULTS

The genomic analysis revealed that 12 CREH strains all carried carbapenemase genes blaNDM-1, blaNDM-5 or blaIMP-26. Although the sequence types (STs) of these 12 strains were relatively diverse, most of the strains (11/12) carried IncHI2 and IncHI2A replicons. Further plasmid analysis showed that carbapenemase genes blaIMP-26 and blaNDM-1 could coexist with mcr-9.1 or mcr-9.2 on IncHI2 plasmids. While the backbones of these IncHI2 plasmids were relatively conserved, the accessory modules carrying the carbapenemase and mcr-9 genes exhibited diverse genetic contexts, involving transposon Tn125, Tn1696 and Tn6725, and integron In27-like, In615b, and In837. Conjugal transfer assay and plasmid stability testing confirmed the transferability and stability of IncHI2 plasmids.

CONCLUSIONS

This study reports the emergence and diversity of IncHI2 plasmids that co-harbour carbapenemase genes and mcr-9.1/9.2 in E. hormaechei. To our knowledge, this is also the first report of blaNDM-1 and mcr-9.2 being carried on a single plasmid in China. The prevalence of such evolutionarily diverse and conjugative carbapenemase-encoding IncHI2 plasmids warrants close monitoring.