Objectives: Hypervirulent Klebsiella pneumoniae (hvKp) ST23-K1 poses a global health threat due to its high virulence and increasing antimicrobial resistance. This study aimed to characterise the genomic feature and phylogenetic evolution of ST23-K1 in China.
Methods: K1 isolates from a nationwide epidemiological surveillance project underwent whole-genome sequencing. Virulence was assessed using hypermucoviscosity phenotyping and a murine infection model. For ST23-K1 carrying acquired antimicrobial resistance genes (ARGs), the CRISPR/Cas system, protospacers, anti-CRISPR (Acr) genes, and plasmidome were characterised. Time-resolved phylogenetic analysis was performed using integrated locally generated and publicly available data.
Results: Among 400 K1 isolates, ST23 was the most prevalent sequence type, and its effective population size increased following CG23-I divergence. The CG23-I sub-lineage was widely distributed nationwide with limited evidence of clonal transmission. Isolates with an incomplete cps locus exhibited significantly reduced virulence compared with those carrying an intact locus. The prevalence of extended-spectrum β-lactamase-positive ST23-K1 isolates increased over time, whereas carbapenemase-producing isolates remained stable. Among acquired ARGs-positive ST23-K1 isolates, a conserved protospacer corresponding to a prevalent spacer was identified. This protospacer, together with AcrIE genes, was frequently co-located on IncFII-type plasmids.
Conclusion: ST23-K1 remains a hypervirulent lineage undergoing ongoing evolutionary expansion. The presence of acquired ARGs in ST23-K1 may be associated with AcrIE-harbouring IncFII plasmids, and functional validation is required to clarify the underlying mechanisms. Continuous genomic surveillance is essential to monitor the evolution and antimicrobial resistance trends of ST23-K1.

Co-authors: Qiucheng Shi, Jingyi Zhu, Rui Weng, Guanhong Lu, Yan Pan, Ping Zhang, Jingjing Quan, Dongdong Zhao, Yunsong Yu, Zhengan Wang