Complete genome sequence of an intestinal carriage Escherichia coli strain L2803 co-harbouring blaNDM-9 and mcr-1 from China.

OBJECTIVES

To define the plasmid-resolved genomic architecture of Escherichia coli L2803, an intestinal carriage isolate co-harbouring blaNDM-9 and mcr-1, and to assess its epidemiological relevance.

METHODS

A faecal isolate from a hospitalised patient was investigated by broth microdilution, S1 nuclease pulsed-field gel electrophoresis (S1-PFGE), Southern blotting and hybrid whole-genome sequencing using short- and long-read data. The complete mcr-1 plasmid was compared with a previously reported related plasmid from the same research setting.

RESULTS

Hybrid assembly showed that L2803 carried blaNDM-9 and mcr-1 on distinct plasmids. Southern blotting localised blaNDM-9 to a plasmid of approximately 120 kb. The complete mcr-1 plasmid, pL2803-mcr-1.1, retained the canonical mcr-1-pap2 module and a highly conserved backbone containing trbL, mobC, mbeA, ymoA, topB, yfhR and xerC. Comparative analysis showed strong similarity to the previously described local plasmid pL2387-mcr-1.1, suggesting persistence of a successful mcr-1 plasmid scaffold in the intestinal reservoir.

CONCLUSIONS

The convergence of blaNDM-9 and mcr-1 in L2803 was mediated by separate plasmid vehicles. This genome note highlights the gut as a reservoir in which a conserved colistin-resistance plasmid can persist while distinct carbapenemase plasmids are acquired, underscoring the value of plasmid-level surveillance of colonising Enterobacterales.