Emergence of hypervirulent and carbapenem-resistant Klebsiella pneumoniae ST37: genomic and phenotypic characterization of virulence and resistance

The emergence and spread of carbapenem-resistant <i>Klebsiella pneumoniae</i> (CRKP) ST37 necessitates urgent reassessment of its pathogenic potential. This study aims to characterize the genomic and phenotypic features of ST37 isolates collected from a tertiary hospital in eastern China, from December 2020 to August 2023. Fifteen CRKP isolates underwent antimicrobial susceptibility testing, whole-genome sequencing (WGS), and phylogenetic analysis for resistance/virulence gene profiling. Phenotypic virulence assays, including quantitative siderophore production, string test, mucoviscosity, capsule quantification, serum resistance, and <i>Galleria mellonella in vivo</i> infection model were designed to evaluate the level of pathogenicity of the isolates. All ST37 <i>Klebsiella pneumoniae</i> isolates exhibited resistance to carbapenems, with 60.0% (9/15) harboring <i>bla</i> _KPC-2 alongside extensive ESBL genes. Critically, a significant subset (26.7%, 4/15; YF1062/YF1072/YF2197/YF2203; KL25/O5) demonstrated hypervirulent phenotypes, evidenced by elevated siderophore production, aerobactin gene carriage (<i>iucABCD</i>/<i>iutA</i>), and extreme lethality in <i>Galleria mellonella</i>, confirming convergent ST37 CRKP-hvKP emergence. This study confirms the emergence of hypervirulent strains within the carbapenem-resistant ST37 lineage, representing a significant convergent threat necessitating urgent surveillance and novel interventions.