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Kingella kingae is an emerging bacterial pathogen that is being recognized increasingly as an important etiology of septic arthritis, osteomyelitis, and bacteremia, especially in young children. Colonization of the posterior pharynx is a key step in the pathogenesis ofK. kingae disease. Previous work established that type IV pili are necessary forK. kingae adherence to the respiratory epithelium. In this study, we set out to identify additional factors that influenceK. kingae interactions with human epithelial cells. We found that genetic disruption of the gene encoding a predicted trimeric autotransporter protein called Knh (K ingellaN hhAh omolog) resulted in reduced adherence to human epithelial cells. In addition, we established thatK. kingae elaborates a surface-associated polysaccharide capsule that requires a predicted ABC-type transporter export operon calledctrABCD for surface presentation. Furthermore, we discovered that the presence of a surface capsule interferes with Knh-mediated adherence to human epithelial cells by nonpiliated organisms and that maximal adherence in the presence of a capsule requires the predicted type IV pilus retraction machinery, PilT/PilU. On the basis of the data presented here, we propose a novel adherence mechanism that allowsK. kingae to adhere efficiently to human epithelial cells while remaining encapsulated and more resistant to immune clearance.IMPORTANCE Kingella kingae is a Gram-negative bacterium that is being recognized increasingly as a cause of joint and bone infections in young children. The pathogenesis of disease due toK. kingae begins with bacterial colonization of the upper respiratory tract, and previous work established that surface hair-like fibers called type IV pili are necessary forK. kingae adherence to respiratory epithelial cells. In this study, we set out to identify additional factors that influenceK. kingae interactions with respiratory epithelial cells. We discovered a novel surface protein called Knh that mediatesK. kingae adherence and found that a surface-associated carbohydrate capsule interferes with the Knh-mediated adherence of organisms lacking pili. Further analysis revealed that pilus retraction is necessary for maximal Knh-mediated adherence in the presence of the capsule. Our results may lead to new strategies to prevent disease due toK. kingae and potentially other pathogenic bacteria.

Modulation of Kingella kingae Adherence to Human Epithelial Cells by Type IV Pili, Capsule, and a Novel Trimeric Autotransporter