Molecular characterization and comparison of -carrying and -harboring IncX3-type plasmids in carbapenem-resistant .

Carbapenem-resistant (CRKP), which harbors the plasmid, has been reported extensively and is considered a global threat clinically. However, characterization and comparisons of -carrying and -harboring IncX3-type plasmids in CRKP are lacking. Here, we systematically compared the differences in the characteristics, genetic backgrounds, transferability, and fitness costs between -carrying and -carrying plasmids in isolates. Fifteen NDM-producing CRKP isolates were recovered from 1376 CRKP isolates between 2019 and 2021, of which 4 were positive for and 11 were positive for . 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 and were located on ~54 kb and ~46 kb IncX3-type plasmids, respectively. The backbone, genetic context, and fitness cost of the -bearing plasmid were highly similar to those of the -carrying plasmid, but the transferability of the -positive plasmid was greater than that of the -positive plasmid. In conclusion, the transmission of or 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 . IMPORTANCE The emergence of NDM-producing is a severe challenge to public health. The widespread presence of and in has aroused broad concern. In this study, we performed molecular characterization of -carrying and -harboring IncX3-type plasmids in carbapenem-resistant (CRKP) and compared their phenotypes between strains with different subtype. Our findings highlight the importance of IncX3-type plasmids in the transfer of the and genes and demonstrate that the 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.