Class C sortases of the SrtBCD pilus cluster involved in the virulence of Streptococcus suis in the mouse model.

Streptococcus suis is an important swine pathogen that severely damages the pig industry worldwide. It’s also a zoonotic pathogen leading to meningitis and streptococcal toxic shock-like syndrome. Although almost 100 virulence-associated factors were identified, the pathogenesis mechanism remains unclear. Three single-gene deletion mutants and one triple-gene deletion mutant were created in order to study the roles of class C sortase, which is ordinarily in charge of pili subunit cell wall anchoring in Gram-positive bacteria. Flow cytometry revealed that the cell wall distribution of major pilin in the same gene cluster is unaffected by the deletion of class C sortases. qRT-PCR verified that the deletion of one sortase gene would influence the transcription of other sortases in the same gene cluster, and the animal challenge assay demonstrated that the virulence of the triple deletion mutant was reduced. Additionally, the in vitro tests using HEp-2 and RAW264.7 cells demonstrated that class C sortase could participate in the initial colonization and anti-phagocytosis steps. Taken together, this study reported the class C sortases in the srtBCD pilus cluster directly involved in the pathological process of S. suis in the mouse model.