Construction of a recombinant attenuated Salmonella enterica serovar Choleraesuis vaccine expressing three antigens of Streptococcus suis and evaluation of its safety and immunogenicity.

Streptococcus suis serotype 2 (SS2) is a major cause of meningitis and septicemia in piglets, prompting a pressing need for safe and effective vaccines amid reduced antibiotic use. In this study, we developed a novel recombinant attenuated Salmonella Choleraesuis vaccine vector, rSC0148, incorporating triple safety systems (delayed lysis, attenuation, and balanced lethality), to deliver a fusion antigen of three SS2 immunogens (SaoA, Eno, and 6PGD), yielding the candidate strain rSC0148(pS-SE6). Our results demonstrated that compared to the wild-type strain C78-3, rSC0148(pS-SE6) showed reduced invasiveness, increased susceptibility to disinfectants, and no environmental shedding post-immunization in piglets. A single dose conferred 100% protection against SS2 in both mice and piglets, and provided 100% (mice) and 80% (piglets) protection against wild-type S. Choleraesuis challenge. These results highlight the strain's strong safety and immunogenicity, offering an innovative platform for S. suis vaccine development and supporting swine disease prevention strategies.