Carbapenemase-producing <b>Klebsiella oxytoca</b> 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: 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.