Genetic and phenotypic characterizations of IncX3 plasmids harboring bla NDM-5 and bla NDM-16b in Japan.

Importance: IncX3 plasmids harboring bla _NDM-5 play a major role in the spread of carbapenem resistance in Asia, particularly in China, in clinical and environmental settings. In this study, we present that Enterobacterales isolates carrying IncX3 plasmids harboring bla _NDM-5 have been disseminated in Japan, where their identification was previously rare. In addition, bla _NDM-16b , a single-nucleotide variant of bla _NDM-5 , was found to be carried by an identical IncX3 plasmid. A comparative sequence analysis revealed that the bla _NDM-16b gene emerged from a single nucleotide substitution on an IncX3 plasmid harboring bla _NDM-5 . The bla _NDM-16b gene did not confer elevated carbapenem resistance compared to bla _NDM-5 in our assay using transformants carrying the plasmid harboring either of these genes, although the A233V substitution was reported to confer stability to the enzyme in ion-depleted conditions. Nevertheless, vigilance regarding the emergence of novel variants is required.
Competing Interests: The authors declare no conflict of interest.