Characterizing Knh: A Multifunctional Kingella Kingae Adhesin
host pathogen interaction
Kingella kingae is an important pathogen in young children and initiates infection by colonizing the posterior pharynx. Adherence to pharyngeal epithelial cells is an important first step in the process of colonization. In the work presented here we examine the characteristics of the Kingella kingae trimeric autotransporter adhesin Knh. Initially, we sought to elucidate the interplay of Knh with type IV pili (T4P) and the polysaccharide capsule in K. kingae adherence to epithelial cells. A strain expressing only Knh is capable of higher levels of adherence under shear stress than a strain expressing only T4P. Examination by various microscopy methods revealed that the capsule has a mean depth of 700 nm and that Knh is approximately 110 nm long. Additional microscopy demonstrated that when bacteria expressing retractile T4P are in close contact with host cells, the capsule is absent at the point of contact between the bacterium and the host cell membrane. Capsule depth remains intact, and adherence levels are markedly reduced with a retraction deficient mutant. These results support the following model: T4P make initial contact with the host cell and mediate low strength adherence. T4P retract, pulling the organism closer to the host cell and displacing the capsule, allowing Knh to be exposed and mediate high strength, tight adherence to the host cell surface. This report provides the first description of the mechanical displacement of capsule enabling intimate bacterial adherence to host cells. Further study of Knh revealed that Knh varies clonally among clinical isolates and contain regions of significant identity and regions of significant variation. Knh variants from clinical isolates are able to mediate adherence to epithelial cells and several extracellular matrix (ECM) proteins. However, the Knh variants vary in the specific ECM proteins to which they adhere. Using the Knh variant from our prototype strain, we observed that both the head and stalk domains of Knh can mediate adherence to epithelial cells and vitronectin. Knh is thus a multifunctional adhesin that is potentially important for colonization and the pathogenesis of K. kingae disease.