Evolutionary Origins and Virulence Determinants of ST25 Hypervirulent Klebsiella pneumoniae in Swine: Genomic Insights and Functional Validation

The global spread of multidrug-resistant hypervirulent Klebsiella pneumoniae (MDR-HvKp), among which carbapenem-resistant strains are of major concern, poses a severe threat to public health due to its high mortality rate and extremely limited treatment options. While human-derived HvKp strains are well-studied, animal-origin variants remain poorly characterized. Here, we isolated a HvKp strain KPB from a swine farm in China, exhibiting high mortality and extreme virulence (LD50 = 20 CFU). Phylogenomic analysis of 342 K. pneumoniae genomes revealed that the swine-derived KPB (sequence type 25 [ST25] lineage) clusters closely with clinical isolates, suggesting zoonotic transmission risks. Targeted mutagenesis identified wcaJ/wzc-mediated capsule synthesis as the critical virulence determinant, with capsule-deficient mutants showing 100% reduced lethality in mouse infection models. Building on this, we developed a phage therapy achieving 100% survival in infected mice at 101 PFU doses. These findings highlight the evolutionary convergence of animal and human HvKp strains and propose phage-based strategies as a promising countermeasure against infections due to HvKp. Our study underscores the urgency of One Health surveillance to mitigate zoonotic threats.