Genetic and phenotypic characterizations of IncX3 plasmids harboring and in Japan.

IncX3 plasmids harboring 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 have been disseminated in Japan, where their identification was previously rare. In addition, , a single-nucleotide variant of , was found to be carried by an identical IncX3 plasmid. A comparative sequence analysis revealed that the gene emerged from a single nucleotide substitution on an IncX3 plasmid harboring . The gene did not confer elevated carbapenem resistance compared to 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.