Phasevarion-Regulated Virulence in the Emerging Pediatric Pathogen Kingella kingae

Abstract

<i>Kingella kingae</i> is a common etiological agent of pediatric osteoarticular infections. While current research has expanded our understanding of <i>K. kingae</i> pathogenesis, there is a paucity of knowledge about host-pathogen interactions and virulence gene regulation. Many host-adapted bacterial pathogens contain phase variable DNA methyltransferases (<i>mod</i> genes), which can control expression of a regulon of genes (phasevarion) through differential methylation of the genome. Here, we identify a phase variable type III <i>mod</i> gene in <i>K. kingae</i>, suggesting that phasevarions operate in this pathogen. Phylogenetic studies revealed that there are two active <i>modK</i> alleles in <i>K. kingae</i> Proteomic analysis of secreted and surface-associated proteins, quantitative PCR, and a heat shock assay comparing the wild-type <i>modK1</i> ON (i.e., in frame for expression) strain to a <i>modK1</i> OFF (i.e., out of frame) strain revealed three virulence-associated genes under ModK1 control. These include the <i>K. kingae</i> toxin <i>rtxA</i> and the heat shock genes <i>groEL</i> and <i>dnaK</i> Cytokine expression analysis showed that the interleukin-8 (IL-8), IL-1β, and tumor necrosis factor responses of THP-1 macrophages were lower in the <i>modK1</i> ON strain than in the <i>modK1</i>::<i>kan</i> mutant. This suggests that the ModK1 phasevarion influences the host inflammatory response and provides the first evidence of this phase variable epigenetic mechanism of gene regulation in <i>K. kingae</i>.