Luck Jennifer N, Tettelin Hervé, Orihuela Carlos J
Department of Microbiology, The University of Alabama at Birmingham, Birmingham, AL, United States.
Department of Microbiology and Immunology, Institute for Genome Sciences, University of Maryland School of Medicine, Baltimore, MD, United States.
Front Cell Infect Microbiol. 2020 Dec 23;10:613287. doi: 10.3389/fcimb.2020.613287. eCollection 2020.
Capsular polysaccharide (CPS), which surrounds the bacteria, is one of the most significant and multifaceted contributors to virulence. Capsule prevents entrapment in mucus during colonization, traps water to protect against desiccation, can serve as an energy reserve, and protects the bacterium against complement-mediated opsonization and immune cell phagocytosis. To date, 100 biochemically and serologically distinct capsule types have been identified for ; 20 to 30 of which have well-defined propensity to cause opportunistic human infection. Among these, serotype 3 is perhaps the most problematic as serotype 3 infections are characterized as having severe clinical manifestations including empyema, bacteremia, cardiotoxicity, and meningitis; consequently, with a fatality rate of 30%-47%. Moreover, serotype 3 resists antibody-mediated clearance despite its inclusion in the current 13-valent conjugate vaccine formulation. This review covers the role of capsule in pneumococcal pathogenesis and the importance of serotype 3 on human disease. We discuss how serotype 3 capsule synthesis and presentation on the bacterial surface is distinct from other serotypes, the biochemical and physiological properties of this capsule type that facilitate its ability to cause disease, and why existing vaccines are unable to confer protection. We conclude with discussion of the clonal properties of serotype 3 and how these have changed since introduction of the 13-valent vaccine in 2000.
包裹在细菌周围的荚膜多糖（CPS）是毒力最重要、最具多面性的促成因素之一。荚膜可防止细菌在定植过程中被困在黏液中，留住水分以抵御干燥，可作为能量储备，并保护细菌免受补体介导的调理作用和免疫细胞吞噬作用。迄今为止，已鉴定出100种生化和血清学上不同的荚膜类型；其中20至30种具有明确的引起人类机会性感染的倾向。其中，3型血清型可能是问题最大的，因为3型血清型感染的特点是具有严重的临床表现，包括脓胸、菌血症、心脏毒性和脑膜炎；因此，死亡率为30%-47%。此外，尽管3型血清型已被纳入目前的13价结合疫苗配方中，但它仍能抵抗抗体介导的清除。本综述涵盖了荚膜在肺炎球菌发病机制中的作用以及3型血清型对人类疾病的重要性。我们讨论了3型血清型荚膜的合成及其在细菌表面的呈现与其他血清型有何不同，这种荚膜类型的生化和生理特性如何促进其致病能力，以及现有疫苗为何无法提供保护。我们最后讨论了3型血清型的克隆特性以及自2000年引入13价疫苗以来这些特性发生了怎样的变化。
