Hernandez Kevin A, Porsch Eric A, Muñoz Vanessa L, St Geme Iii Joseph W
University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, United States of America.
Department of Pediatrics, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, United States of America.
PLoS Pathog. 2025 Sep 2;21(9):e1013473. doi: 10.1371/journal.ppat.1013473. eCollection 2025 Sep.
Kingella kingae is a Gram-negative bacterium that has emerged as a leading cause of invasive disease in children between 6 months and 4 years of age. K. kingae initiates infection by colonizing the oropharynx, then breaches the oropharyngeal epithelium, enters the bloodstream, and disseminates to distant sites to cause disease, including osteomyelitis, septic arthritis, and endocarditis. To survive in the bloodstream and disseminate to sites of invasive disease, K. kingae produces a polysaccharide capsule and an exopolysaccharide that inhibit opsonin deposition and mediate resistance to complement-mediated serum killing. However, elimination of these extracellular polysaccharides only partially reduces K. kingae survival in human serum, suggesting that additional factors contribute to serum resistance. In this study, we found that K. kingae binds human factor H (FH), a negative regulator of the alternative complement pathway. In experiments using rat serum as a source of complement, we observed that K. kingae was able to utilize human FH to resist killing. Introduction of exogenous human FH into the juvenile rat infection model of K. kingae disease enhanced virulence in vivo, demonstrating the importance of FH binding in the pathogenesis of disease. Far-western blot analysis identified a 37-kDa outer membrane protein designated KK02920 that was responsible for FH binding and enhanced virulence in vivo in the presence of human FH. Loss of KK02920 virtually abrogated serum resistance, indicating that KK02920 is the major determinant of K. kingae serum resistance. Additional analysis revealed the presence of KK02920 across a collection of serum-resistant invasive and carrier K. kingae isolates, all of which can utilize human FH to resist complement-mediated killing. This work demonstrates the importance of a complement-regulator binding protein as a major mechanism of serum resistance in an encapsulated organism.
金氏金杆菌是一种革兰氏阴性菌，已成为6个月至4岁儿童侵袭性疾病的主要病因。金氏金杆菌通过定植于口咽部引发感染，随后突破口咽上皮，进入血液，并扩散至远处部位引发疾病，包括骨髓炎、化脓性关节炎和心内膜炎。为了在血液中存活并扩散至侵袭性疾病部位，金氏金杆菌产生一种多糖荚膜和一种胞外多糖，它们可抑制调理素沉积并介导对补体介导的血清杀伤的抗性。然而，去除这些细胞外多糖仅部分降低了金氏金杆菌在人血清中的存活率，这表明还有其他因素导致血清抗性。在本研究中，我们发现金氏金杆菌与人因子H（FH）结合，FH是替代补体途径的负调节因子。在使用大鼠血清作为补体来源的实验中，我们观察到金氏金杆菌能够利用人FH抵抗杀伤。将外源性人FH引入金氏金杆菌疾病的幼鼠感染模型中可增强体内毒力，证明FH结合在疾病发病机制中的重要性。Far-western印迹分析鉴定出一种37 kDa的外膜蛋白，命名为KK02920，它负责FH结合并在存在人FH的情况下增强体内毒力。KK02920的缺失几乎消除了血清抗性，表明KK02920是金氏金杆菌血清抗性的主要决定因素。进一步分析显示，在一系列血清抗性侵袭性和携带金氏金杆菌分离株中均存在KK02920，所有这些分离株都能利用人FH抵抗补体介导的杀伤。这项工作证明了补体调节因子结合蛋白作为包膜生物体血清抗性主要机制的重要性。
