Outer membrane vesicles mediating horizontal transfer of the epidemic bla_OXA-232 carbapenemase gene among Enterobacterales

ABSTRACT

OXA-232 is one of the most common OXA-48-like carbapenemase derivatives and is widely disseminated in nosocomial settings across countries. The bla_OXA-232 gene is located on a 6-kb non-conjugative ColKP3-type plasmid, while the dissemination of bla_OXA-232 into different Enterobacterales species and the polyclonal dissemination of OXA-232-producing K. pneumoniae revealed the horizontal transfer of bla_OXA-232. However, it’s still unclear how this non-conjugative ColKP3 plasmid could facilitate the mobilization of bla_OXA-232. Here, we observed the in vivo intraspecies transfer of bla_OXA-232 during a nosocomial outbreak of OXA-232-producing K. pneumoniae. We demonstrated the presence of ColKP3 OXA-232 plasmid in the outer membrane vesicles (OMVs) derived from clinical isolates, and OMVs could facilitate the horizontal transfer of bla_OXA-232 among Enterobacterales. In contrast, for the most prevalent carbapenemase genes, including bla_KPC-2 and bla_NDM-1, though the presence of carbapenemase genes and plasmid backbones in the vesicular lumen was observed, OMVs couldn’t promote effective transformation, probably due to the low copy number of plasmids in clinical isolates and the low number of plasmids loaded into vesicles. Conjugation assay revealed that the epidemic IncX3 NDM-1 and IncFII(pHN7A8)/IncR KPC-2 plasmids were conjugative and could be horizontally transferred via independent conjugation or with the help of a co-existent conjugative plasmid. For the large-size and low-copy number conjugative plasmids carrying carbapenemase genes, OMVs-mediated gene exchange may only serve as an alternative pathway for horizontal transfer. In conclusion, diverse mobilization strategies were employed by plasmids harbouring carbapenemase genes, and plasmids display a proper choice of mobility pathway due to their individual properties.

KEYWORDS:

• OXA-232
• outer membrane vesicles
• horizontal gene transfer
• carbapenemase genes
• plasmid mobility

Acknowledgements

We thank the authority of CR-hvKP4 by Prof. Rong Zhang from the Second Affiliated Hospital of Zhejiang University School of Medicine. We thank the authority of Kp1902226 by Prof. Xing Wang from Shanghai Children’s Medical Center.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Ethical approval

All procedures performed in this study involving human participants were in accordance with the ethical standards of the Institutional Review Board Ethics Committee of Renji Hospital. For this type of retrospective study, formal consent is not required.

Nucleotide sequence accession numbers

Genome sequences of all OXA-232-producing K. pneumoniae strains have been deposited in the NCBI database under BioProject accession numbers PRJNA1001133.

Transparency declarations

The authors declare that they have no competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Additional information

Funding

This study was supported by National Natural Science Foundation of China (82272374), Shanghai Pujiang Program (22PJ1409600), and a research fund from Renji Hospital for young scholars (RJTJ22-MS-018). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.