Natural variation of hypervirulent Klebsiella pathogenicity loci among Taiwan bloodstream isolates

ABSTRACT Klebsiella pneumoniae is a major cause of both nosocomial and community-acquired infections, with hypervirulent (hvKP) strains causing severe disease in healthy individuals. In Southeastern Asia, diabetes mellitus is a recognized risk factor for hvKP-associated pyogenic liver abscesses. hvKP virulence is typically attributed to carriage of a large virulence plasmid encoding siderophore biosynthesis ( iuc , iro ) and mucoid regulator ( rmpA , rmpA2 ) genes. Here, we analyzed 50 bloodstream isolates from Taipei, Taiwan, to investigate genomic and phenotypic characteristics of isolates from patients with or without diabetes mellitus. In diabetic patients and patients with liver abscesses, hvKP biomarkers were found in 66% ( n = 33) and 64% ( n = 32) of isolates, respectively. While we expected hvKP isolates to be overrepresented in this collection, we observed extensive diversity among hvKP pathogenicity loci, with strains of typical ST23 hvKP lineages carrying incomplete KpVP-1 virulence plasmids. This hvKP biomarker diversity is typically found in classical multidrug-resistant lineages that have acquired portions of the virulence plasmid. Phenotypic assays showed that hvKP biomarkers did not strictly predict hypermucoviscosity, capsule and siderophore production, or survival in serum. Loss of rmpA consistently eliminated hypermucoviscosity and reduced virulence in a murine pneumonia model, whereas aerobactin loss did not. In vivo studies demonstrated variations in virulence that could not be explained solely by differences in the number of hypervirulence-associated loci. These findings highlight the complexity of K. pneumoniae pathogenesis and demonstrate that while canonical biomarkers effectively distinguish hvKP from classical K. pneumoniae , they are insufficient to predict variation in virulence among hvKP strains. Our findings provide insight into the virulence spectrum of strains carrying incomplete plasmid configurations. IMPORTANCE K. pneumoniae poses a global health threat due to the convergence of antimicrobial resistance and hypervirulence. We identified substantial diversity in virulence plasmid content, including incomplete virulence plasmids within archetypal hvKP lineages, and showed that phenotypic and in vivo virulence traits cannot be fully explained by the presence or absence of individual hypervirulence-associated loci. While canonical biomarkers such as rmpA and iuc are widely used to distinguish hypervirulent strains, our analysis demonstrates that no single biomarker is sufficient to reliably predict pathogenic potential and that virulence depends on specific locus combinations and broader context. These findings highlight a critical gap in our understanding of hvKP pathogenesis, underscoring the need for more nuanced frameworks to evaluate virulence. This work has important implications for clinical diagnostics, surveillance, and risk assessment of emerging K. pneumoniae strains worldwide.