Kingella kingae is a Gram negative bacterium of Neisseriaceae family that colonizes throat of young children and is transmitted from child-to-child through close personal contact. The bacterium is an emerging pathogen and is the leading cause of osteomyelitis and septic arthritis in pediatric patients younger than four years old. Complications of osteoarticular infections in children include abnormalities in bone growth, limitation of joint mobility, unstable joint articulation, and chronic joint dislocation, resulting in residual skeletal dysfunction in 10- 25% of cases. In recent years, b-lactamase activity has emerged in K. kingae and is now present in ~25% of isolates. Many of these isolates are resistant to other antibiotics as well, raising concern about approaches to treatment in the future, especially given the potential for rapid spread of antibiotic resistance in other members of the Neisseriaceae family. At present there are no effective strategies to prevent K. kingae disease and the associated morbidity. Despite the growing appreciation of the role of K. kingae as a pathogen, our knowledge on pathophysiological effect of K. kingae on skeletal tissue is limited. In this project we propose to elaborate novel experimental systems to study the sequelae of the bone infections due to this understudied pathogen. We will assess the femur osteomyelitis, one of the most common clinical presentation of K. kingae infection, by direct injection of the bacteria in the infant rats’ femur. Additionally, we will characterize hematogenously acquired K. kingae bone infections. Using state-of-the art technologies, including micro-computed tomography (microCT) analysis and highly sensitive in vivo imaging, we will define the inflammatory response and pathology features in the bone microenvironment. The availability of a well-characterized model would aid greatly to understanding the pathology features of K. kingae induced pediatric osteomyelitis. Key virulence factors in K. kingae include a potent RTX-toxin that can affect different cell types. The experimental system will be used to investigate the role of RtxA in the K. kingae pathogenesis. K. kingae biofilm formation on bone will be evaluated using in vivo and in vitro systems. .