Phasevarion-Regulated Virulence in the Emerging Pediatric Pathogen Kingella kingae.

is a common etiological agent of pediatric osteoarticular infections. While current research has expanded our understanding of 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 ( 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 gene in , suggesting that phasevarions operate in this pathogen. Phylogenetic studies revealed that there are two active alleles in Proteomic analysis of secreted and surface-associated proteins, quantitative PCR, and a heat shock assay comparing the wild-type ON (i.e., in frame for expression) strain to a OFF (i.e., out of frame) strain revealed three virulence-associated genes under ModK1 control. These include the toxin and the heat shock genes and 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 ON strain than in the :: 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 .