Formononetin alleviates Streptococcus suis infection by targeting suilysin

Streptococcus suis serotype 2 (SS2) has become a leading pathogen responsible for swine industry and human infections, causing enormous economic loss and triggering food safety risk. New and alternative strategies for combating this microorganism are urgently needed. Suilysin (SLY), a pore-forming toxins produced by SS2 has been revealed play critical role during its infection and could be an ideal target for combating this pathogen. Here, we found that formononetin (Form) inhibited the haemolytic activity of SLY without exerting growth pressure on SS2 or affecting the expression of SLY. At the cellular infection level, Form treatment diminished the cytotoxicity induced by SLY or SS2 and inflammatory response induced by SS2. In addition, the treatment with Form reduced bacterial burden in livers and spleens in SS2 infected mice. These data revealed that Form could attenuate the pathogenesis of SS2 both in vitro and in vivo by targeting SLY, suggesting that this compound could be used in combating S. suis infections.