Abstract
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.
Highlights
The capsular polysaccharide (CPS) of Streptococcus suis defines various serotypes based on its composition and structure
Serotype switching in S. suis has not yet been demonstrated, these findings suggest that replacement of the cps gene clusters may occur in strains in the competent state through up-take of genomic DNA of the other serotype strains from the environment
Serotype-switched S. suis mutants were generated from serotype 2 to serotypes 3, 4, 7, 8, 9 or 14 via induction of competence state using XIP, which is the first report experimentally demonstrating full cps locus exchange in S. suis
Summary
The capsular polysaccharide (CPS) of Streptococcus suis defines various serotypes based on its composition and structure. The effects of serotype switching were 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 proinflammatory 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, some different mutations other than loci of CPS-related genes were found in each the serotype-switched mutant. Serotype switching in S. suis has not yet been demonstrated, these findings suggest that replacement of the cps gene clusters may occur in strains in the competent state through up-take of genomic DNA of the other serotype strains from the environment
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