Affiliation:
1. Antimicrobial Resistance Research Center, National Institute of Infectious Diseases , Tokyo, Japan
Abstract
ABSTRACT
The spread of the gene encoding the NDM-type carbapenemase,
bla
NDM
, poses a serious threat to clinical practice and public health. This gene is usually carried by transferable plasmids, which facilitates its rapid spread among various species of Enterobacterales. Plasmids with the IncX3 replicon play a major role in the spread of
bla
NDM
in Asian countries. In this study, we conducted genomic sequencing and a comparative analysis of the IncX3-type plasmids harboring
bla
NDM-5
and
bla
NDM-16b
, a single-nucleotide variant of
bla
NDM-5
, isolated in a national antimicrobial-resistant bacterial genomic surveillance in Japan (Japan Antimicrobial Resistant Bacterial Surveillance), which was carried out during 2019–2020. We compared five plasmids harboring
bla
NDM-5
and one plasmid harboring
bla
NDM-16b
. They were highly identical and differed in several nucleotide substitutions or variations in insertion sequences, although they were carried by different species or genotypes. Notably,
bla
NDM-16b
-carrying pJBBDACG-19-0070 was identical to a plasmid carrying
bla
NDM-5
except for one nucleotide substitution in the
bla
NDM
gene throughout the 46 kb sequences. Transformants carrying these two plasmids showed comparative resistance to carbapenems, indicating that a substitution on the NDM enzyme (Ala233 to Val) did not affect carbapenem resistance, at least under normal experimental conditions. A database search revealed that several identical plasmids carrying
bla
NDM-5
were reported from neighboring countries, mainly China, before our surveillance period. Our analysis suggested that the IncX3 plasmid harboring
bla
NDM-5
is spreading in Japan, and
bla
NDM-16b
emerged from a single nucleotide substitution on the plasmid, with widespread dissemination in Asian countries.
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.
Funder
Japan Agency for Medical Research and Development
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Cell Biology,Microbiology (medical),Genetics,General Immunology and Microbiology,Ecology,Physiology