Phenotypic and Genotypic Characteristics of Hypervirulent Klebsiella pneumoniae (hvKp): A Narrative Review.

Hypervirulence, an emerging term used to describe an ability of pathogen to survive in harsh environments, is particularly suited to the enigmatic Klebsiella pneumoniae (Kp). Numerous studies are underway to comprehend how this bacterium evolve into hypervirulent forms. While K. pneumoniae typically affects immunocompromised individuals in hospital settings as an opportunistic pathogen, certain strains are capable of infecting healthy individuals in community settings. This observation triggered the researchers to recognize the emergence of a new pathotype in Kp and termed it into "Hypervirulence." Nevertheless, the differentiation of hypervirulent from the classical strains became a great challenge in hospital settings and research laboratories as well. This review addresses the critical challenge of differentiating hvKp from cKp by evaluating phenotypic traits, such as hypermucoviscosity, siderophore overproduction, and enhanced biofilm formation, alongside genotypic markers, including various key virulence genes and specific capsular serotypes. Additionally, virulence gene expression level in various environmental stress, pathogenicity assays using in vitro serum resistance and immune cell models, and in vivo animal or insect models provide functional confirmation of hypervirulence. The integration of these phenotypic, genotypic, virulence gene expression level, and pathogenicity-based approaches enables accurate identification of hvKp, thereby resolving the diagnostic dilemma and improving clinical management and epidemiological surveillance of this increasingly significant pathogen.