Division of Bacterial and Parasitic Diseases, National Institute of Animal Health, National Agriculture and Food Research Organization, Tsukuba, Ibaraki, Japan.
Faculty of Veterinary Medicine, University of Montreal, Saint-Hyacinthe, QC, Canada.
Sci Rep. 2021 Mar 22;11(1):6513. doi: 10.1038/s41598-021-85882-3.
The capsular polysaccharide (CPS) of Streptococcus suis defines various serotypes based on its composition and structure. Though serotype switching has been suggested to occur between S. suis strains, its impact on pathogenicity and virulence remains unknown. Herein, we experimentally generated S. suis serotype-switched mutants from a serotype 2 strain that express the serotype 3, 4, 7, 8, 9, or 14 CPS. The effects of serotype switching were then investigated with regards to classical properties conferred by presence of the serotype 2 CPS, including adhesion to/invasion of epithelial cells, resistance to phagocytosis by macrophages, killing by whole blood, dendritic cell-derived pro-inflammatory mediator production and virulence using mouse and porcine infection models. Results demonstrated that these properties on host cell interactions were differentially modulated depending on the switched serotypes, although some different mutations other than loci of CPS-related genes were found in each the serotype-switched mutant. Among the serotype-switched mutants, the mutant expressing the serotype 8 CPS was hyper-virulent, whereas mutants expressing the serotype 3 or 4 CPSs had reduced virulence. By contrast, switching to serotype 7, 9, or 14 CPSs had little to no effect. These findings suggest that serotype switching can drastically alter S. suis virulence and host cell interactions.
猪链球菌荚膜多糖 (CPS) 根据其组成和结构定义了不同的血清型。虽然已经提出血清型转换可能发生在 S. suis 菌株之间，但它对致病性和毒力的影响尚不清楚。在此，我们从血清型 2 菌株中实验性地产生了表达血清型 3、4、7、8、9 或 14 CPS 的血清型转换突变体。然后，我们通过使用小鼠和猪感染模型，研究了血清型转换对存在血清型 2 CPS 赋予的经典特性的影响，包括对上皮细胞的粘附/入侵、对巨噬细胞吞噬作用的抗性、全血杀伤、树突状细胞衍生的促炎介质产生和毒力。结果表明，这些与宿主细胞相互作用的特性根据转换的血清型而不同调节，尽管在每个血清型转换突变体中都发现了除 CPS 相关基因座之外的一些不同突变。在血清型转换突变体中，表达血清型 8 CPS 的突变体具有超毒力，而表达血清型 3 或 4 CPS 的突变体的毒力降低。相比之下，转换为血清型 7、9 或 14 CPS 几乎没有影响。这些发现表明血清型转换可以极大地改变 S. suis 的毒力和宿主细胞相互作用。
