Cloning, expression and characterization of a cell wall surface protein, 6-phosphogluconate-dehydrogenase, of Streptococcus suis serotype 2

Streptococcus suis type 2 is a pathogen responsible for diverse diseases in both pigs and humans. In order to understand the pathogenesis of the S. suis type 2 infection, the gene encoding a cell surface protein, 6-phosphogluconate-dehydrogenase (6PGD) of S. suis type 2 was cloned and sequenced, and recombinant 6PGD protein (r6PGD) was produced in a prokaryotic expression system. Sequence analysis of the cloned 6 pdg gene showed 82% similarity with Streptococcus pneumoniae 6 pdg at the nucleic acid level. Western blotting using r6PGD-specific antiserum confirmed the cell surface location of the 6PGD protein of S. suis type 2. The role of 6PGD in S. suis type 2 pathogenesis as an adhesin and its immunogenicity in mice was further investigated. The results showed that the recombinant protein interfered with the adhesion of S. suis type 2 to Hep2 and HeLa cells by 72% and 66%, respectively. Immunization of CD-1 mice with r6PGD increased the protective efficacy by 80% following intraperitoneal administration of a lethal dose of S. suis type 2. Immunization of CD-1 mice with r6PGD elicited a significant protective immune response, which demonstrated the importance of 6PGD to bacterial pathogenesis. Identification and characterization of the role of S. suis type 2 6PGD in adhesion and immunogenicity will allow us to use this protein to develop new antimicrobial therapies and/or vaccines.