UspF Regulates Type III Pili-Mediated Adhesion, Oxidative Stress Resistance, and Virulence in Klebsiella pneumoniae

<i>Klebsiella pneumoniae</i> (<i>K. pneumoniae</i>, <i>KP</i>) is a significant opportunistic pathogen responsible for both nosocomial and community-acquired infections. Bacterial adhesion is the critical initial step for host colonization and the establishment of disease. In this study, we utilized a mariner transposon mutagenesis system to construct a mutant library from the clinical <i>KP</i> strain <i>KP</i>20, identifying a mutant with significantly impaired epithelial cell adhesion due to an insertion in the <i>uspF</i> gene. Genetic knockout experiments confirmed that <i>uspF</i> deletion markedly reduced the adhesion to human airway epithelial cells (Calu-3) and downregulated the transcription of type III pili-encoding genes (<i>mrkABDF</i>). Furthermore, <i>uspF</i> deficiency compromised antioxidant stress and serum resistance and increased susceptibility to dendritic cell and macrophage phagocytosis. In vivo challenge experiments further demonstrated that <i>uspF</i> deletion significantly attenuated <i>K. pneumoniae</i> virulence in mice. These findings provide important insights into the molecular pathogenesis of <i>K. pneumoniae</i> and identify UspF as a potential target for therapeutic intervention.