The genetically modified suilysin, rSLYP353L, provides a candidate vaccine that suppresses proinflammatory response and reduces fatality following infection with Streptococcus suis

Streptococcus suis is a persistent global hazard in the swine industry and an emerging threat to public health. The high mortality in China following outbreaks of streptococcal toxic shock syndrome (STSS) underscores the urgency for effective prevention. A limited understanding of the pathogenesis of S. suis in STSS may explain the lack of biological products for prevention. Suilysin (SLY) is an important virulence factor in the pathogenesis of S. suis. To identify a candidate vaccine for S. suis-induced STSS, we constructed a recombinant non-hemolytic mutant of SLY that has hemagglutination activity, rSLYP353L, and evaluated its ability to induce inflammatory response and prevent fatal S. suis infection in mice. The rSLYP353L mutant, as compared with hemolytic rSLY, elicited lower levels of IL-6, KC and IL-10 at 3 h and 5 h post-treatment (p < 0.05), indicating that hemolytic activity is associated with rSLY-mediated inflammation. Furthermore, passive immunization with anti-SLYP353L antisera protected mice from acute death after infection with S. suis SC84 (p < 0.05). Effects were not due to protection against tissue damage, as S. suis SC84 caused no detectable histopathological lesions in mice within 24 h. However, immunization with rSLYP353L caused significantly reduced levels of KC and IL-1β at 6 and 9 h post-challenge and IL-6 at 9 h post-challenge (p < 0.05). In conclusion, rSLYP353L may provide a potential vaccine for protection against S. suis-induced STSS due to its reduction in proinflammatory response early in S. suis infection.