Genetic characterization of KHM-1 metallo-β-lactamase-producing Enterobacterales isolates from inpatient sources in Osaka, Japan.

Objectives: KHM-1-metallo-β-lactamase-producing Enterobacterales strains, of which only a few have been found, were isolated from four inpatients in Osaka, Japan during 2016 to 2020. We compared whole genomes of the four KHM-1-producing isolates, including one Enterobacter hormaechei subsp. hoffmannii, one Escherichia coli, and two Citrobacter freundii.

Methods: These isolates were characterized by whole-genome sequencing, comparative analysis of bla-encoding plasmids with earlier reported plasmids, and antimicrobial susceptibility tests.

Results: Multilocus sequence typing classified the E. hormaechei subsp. hoffmannii isolate to ST78, the E. coli isolate to ST354, and the two C. freundii isolates to ST95. These isolates harboured various antimicrobial resistance genes aside from bla on their chromosomes and plasmids. In all four isolates, bla was located on 137 kbp to 213 kbp plasmids of IncC replicon type. Although there were common resistance genes such as bla-ISEc68, class I integron cassette, and fosG, the four bla-encoding plasmids were distinguishable into two lineages based on differences of the resistance gene components and their surrounding regions.

Conclusion: Because no epidemiological contact was observed among the inpatients, the bla-encoding IncC plasmids might have spread horizontally to multiple bacterial species through repeated recombination and insertion.