Identification and characterization of novel immunogenic proteins of Streptococcus suis serotype 2.

Streptococcus suis, a zoonotic pathogen, caused serious outbreaks in humans with high mortality rates in the past decade. To develop safer and more effective vaccines, particularly for human protection, cell wall and extracellular proteins of S. suis serotype 2 were analyzed by an immunoproteomic approach in this study. Thirty-two proteins with high immunogenicity were identified and 22 of them were newly identified. Further analyses of 9 selected proteins revealed that (1) these 9 proteins were expressed in all tested virulent S. suis serotype 2 isolates, (2) antisera against 6 of the selected proteins efficiently killed the bacteria by opsonized phagocytosis in human blood, and (3) significantly higher levels of serum antibodies against 3 proteins were detected in both patients and infected swines. Therefore, our results suggest the 3 proteins (SSU98_0197, SSU98_1094 and SSU1664) have strong potential to be vaccine candidates.