The Novel PhoP/VirK Regulatory Axis Synergistically Drives Antibiotic Resistance and Virulence in Klebsiella pneumoniae
The genetic connection between virulence and antibiotic resistance remains poorly understood. Our previous RNA-Seq analysis of a polymyxin-resistant Klebsiella pneumoniae ATCC BAA2146 mutant identified a highly expressed VirK/YbjX family gene (kpn2146_RS17285), encoding a conserved membrane protein, designated virK (virulence required for Klebsiella pneumoniae). This study investigates the function and regulation of virK and its role in linking polymyxin resistance and virulence through the PhoP/VirK axis. VirK localizes to the outer membrane and, although not involved in lipopolysaccharide modification, its deletion markedly reduced bacterial virulence in a mouse systemic infection model. Transcriptional and electrophoretic mobility shift assays demonstrated that virK is directly activated by the PhoP protein. A strong positive correlation between virK and phoP expression (r=0.98) was also observed in multidrug-resistant clinical isolates. Since the PhoP/PhoQ two-component system mediates polymyxin resistance, its direct regulation of VirK uncovers an adaptive mechanism coupling enhanced virulence with antibiotic resistance. These findings reveal a previously unrecognized PhoP/VirK regulatory pathway that synergistically promotes resistance and pathogenicity, offering new insights into bacterial evolution and suggesting that targeting this axis could provide an effective strategy to combat multidrug-resistant K. pneumoniae infections.