Dissemination and Stability of the bla NDM-5 -Carrying IncX3-Type Plasmid among Multiclonal Klebsiella pneumoniae Isolates

The emergence and spread of New Delhi metallo-β-lactamase (NDM)-producing Enterobacteriaceae have been a serious challenge to public health, and NDM-5 shows increased resistance to carbapenems compared with other variants. NDM-5 has been identified mostly in E. coli but has rarely been described in K. pneumoniae and other Enterobacteriaceae isolates. Here, we present the dissemination of highly similar 46-kb IncX3 bla NDM-5 -carrying plasmids among multiclonal K. pneumoniae strains in children, highlighting the horizontal gene transfer of bla NDM-5 among K. pneumoniae strains via the IncX3 plasmid. Moreover, the IncX3 bla NDM-5 -carrying plasmids displayed strong stability in clinical strains when cultured in antibiotic-free medium, and the plasmid maintenance was attributed partly to conjugal transfer. Plasmid conjugation is mediated by the type IV secretion system (T4SS), and T4SS is conserved among all epidemic IncX3 bla NDM-5 -carrying plasmids. Therefore, combining conjugation inhibition and promotion of plasmid loss would be an effective strategy to limit the conjugation-assisted persistence of IncX3 bla NDM-5 -carrying plasmids.