Co-Occurrence of NDM-9 and MCR-1 in a Human Gut Colonized ST1011.

Background: The emergence of the plasmid-borne colistin-resistant gene () poses a great threat to human health. What is worse, the recent observations of the coexistence of with carbapenemase encoding genes in some bacteria caused even more concern. Yet, there is a lack of observations of such strains in the human gut.

Methods: The isolation of L889 was performed on selective medium plates. Antibiotic susceptibilities were determined by an agar dilution and a broth microdilution method. Multi-locus sequence typing (MLST) and acquired resistance genes were also characterized. Transferability of /-carrying plasmids was determined by conjugation, replicon typing and S1-Pulsed-field gel electrophoresis (S1-PFGE), and Southern blotting. The sequences of these plasmids were analyzed by using whole-genome sequencing with Illumina Novaseq and Nanopore platforms.

Results: L889 was identified as ST1101 concomitantly carrying and from a stool sample. Antimicrobial susceptibility tests showed that it was resistant to various antimicrobial agents and only susceptible to tigecycline. Notably, was located on a ~114-kb untypable plasmid, while was located on a ~63-kb IncI2 plasmid.

Conclusion: Our research, to our knowledge, first reported an ST1101 strain with an untypeable -harbouring plasmid and an IncI2 -carrying plasmid. The colonized strains potentially contribute to the dissemination and transfer of and to clinical isolates, which is a considerable threat to public health and should be closely monitored.