Carbapenemase-producing Klebsiella oxytoca complex in France (2017-2023): molecular epidemiology integrated with virulence and biofilm phenotypes.

OBJECTIVES

This study analysed a large French collection of carbapenemase-producing Klebsiella oxytoca complex (KoC) isolates (2017-2023) to map species and carbapenemase distributions and identify emerging lineages. We further investigated virulence traits to understand the epidemiological success of the dominant ST-2 lineage.

METHODS

We conducted a retrospective study of all KoC isolates received at the French National Reference Center for Antimicrobial Resistance from 2017 to 2023. Whole-genome sequencing was performed to assess species assignment, phylogeny, and sequence types. Virulence analyses included biofilm formation assays (on abiotic surfaces and eukaryotic cells) and Galleria mellonella infection models.

RESULTS

K. oxytoca sensu stricto remained the most prevalent species among the KoC. OXA-48-like enzymes were the most common carbapenemases, and two major lineages predominated: ST-141 and, far ahead, ST-2. The success of ST-2 appears linked to its low virulence combined with a strong capacity for long-term persistence.

CONCLUSION

Our findings confirm that K. oxytoca comprises a complex of distinct species whose taxonomy warrants continued revision. ST-2 circulates widely in France and, despite its limited virulence, shows remarkable persistence, making it an epidemiological important lineage.