Molecular characterization and comparison of bla (NDM-1)-carrying and bla (NDM-5)-harboring IncX3-type plasmids in carbapenem-resistant Klebsiella pneumoniae

Carbapenem-resistant Klebsiella pneumoniae (CRKP), which harbors the bla (NDM) plasmid, has been reported extensively and is considered a global threat clinically. However, characterization and comparisons of bla (NDM-1)-carrying and bla (NDM-5)-harboring IncX3-type plasmids in CRKP are lacking. Here, we systematically compared the differences in the characteristics, genetic backgrounds, transferability, and fitness costs between bla (NDM-1)-carrying and bla (NDM-5)-carrying plasmids in K. pneumoniae isolates. Fifteen NDM-producing CRKP isolates were recovered from 1376 CRKP isolates between 2019 and 2021, of which 4 were positive for bla (NDM-1) and 11 were positive for bla (NDM-5). All strains were highly resistant to carbapenem but remained susceptible to tigecycline and colistin. Core-genome-based phylogenetic analyses revealed that these strains were not clonally related. Whole-genome sequencing showed that bla (NDM-1) and bla (NDM-5) were located on ~54 kb and ~46 kb IncX3-type plasmids, respectively. The backbone, genetic context, and fitness cost of the bla (NDM-1)-bearing plasmid were highly similar to those of the bla (NDM-5)-carrying plasmid, but the transferability of the bla (NDM-1)-positive plasmid was greater than that of the bla (NDM-5)-positive plasmid. In conclusion, the transmission of bla (NDM-1) or bla (NDM-5) is mainly disseminated by plasmids rather than clonal spread. The high transfer frequency of the IncX3 plasmid facilitates the prevalence and dissemination of NDM-KP among Enterobacteriaceae. IMPORTANCE: The emergence of NDM-producing Klebsiella pneumoniae is a severe challenge to public health. The widespread presence of bla (NDM-1) and bla (NDM-5) in Enterobacteriaceae has aroused broad concern. In this study, we performed molecular characterization of bla (NDM-1)-carrying and bla (NDM-5)-harboring IncX3-type plasmids in carbapenem-resistant Klebsiella pneumoniae (CRKP) and compared their phenotypes between strains with different bla (NDM) subtype. Our findings highlight the importance of IncX3-type plasmids in the transfer of the bla (NDM-1) and bla (NDM-5) genes and demonstrate that the bla (NDM-1) plasmid possesses higher transfer ability. These data will provide important insights into carbapenem resistance gene transfer via plasmids and their further spread in clinical settings.