Clonal diversity and plasmid-mediated emergence of NDM-1-producing Raoultella ornithinolytica in clinical isolates.

OBJECTIVE

Raoultella ornithinolytica is recognized as an emerging opportunistic pathogen, with sporadic reports of multidrug resistance. However, comprehensive analyses of carbapenem-resistant isolates remain limited. This study investigated the molecular features and plasmid-mediated transmission of blaNDM-1 among clonally distinct clinical isolates of R. ornithinolytica in Seoul, South Korea.

METHODS

All 13 carbapenem-resistant R. ornithinolytica isolates referred to the central reference laboratory in Seoul from seven hospitals between 2018 and 2020 were analysed. Isolates were characterized using antimicrobial susceptibility testing, resistance gene detection, plasmid replicon typing, pulsed-field gel electrophoresis, conjugation assays, and whole-genome sequencing.

RESULTS

Among the 13 isolates, 10 harboured blaNDM-1, seven of which carried the gene on IncX3 plasmids. Despite clonal diversity, six of the 13 isolates shared nearly identical transferable IncX3 plasmids of approximately 45 kb, indicating horizontal plasmid dissemination among non-clonal strains. A novel blaNDM-1 configuration, IS3000-∆ISAba125-IS1A-blaNDM-1-bleMBL-trpF, was found in both R. ornithinolytica and Enterobacter cloacae from a single hospital, including two patients with co-infection. These findings highlighting the key role of IncX3 plasmids in rapid dissemination of blaNDM-1 across species boundaries.

CONCLUSIONS

This study demonstrates the contribution of IncX3 plasmids to the intra- and interspecies spread of blaNDM-1, underscoring the need for enhanced genomic surveillance of emerging pathogens such as R. ornithinolytica to limit carbapenem resistance transmission in clinical settings.