Immunoproteomic assay of surface proteins of Streptococcus suis serotype 9

Streptococcus suis is an important swine pathogen responsible for a diverse group of diseases. Studies on vaccines have focused on S. suis serotype 2 strains, which are the most invasive isolates worldwide. However, in China S. suis serotype 9 (SS9) is also a prevalent serotype, which is frequently isolated from diseased pigs. Little is known about immunogenic proteins for SS9. Therefore, an immunoproteomic-based approach was developed to identify immunogenic proteins of SS9. Cell wall proteins extracted from SS9 strain GZ0565 isolated from a diseased pig with meningitis were screened by two-dimensional Western blotting using anti-SS9 sera pooled from specific pathogen-free mice. Protein spots were excised from preparative gels and identified by matrix-assisted laser desorption ionization time-of-flight MS (MALDI-TOF-MS) or MALDI-TOF-TOF-MS, which led to the identification of eight immunogenic proteins (arginine deiminase, extracellular solute-binding protein, translation elongation factor Ts, neprilysin, peptide ATP-binding cassette transporter peptide-binding protein, pyruvate kinase, phosphate acetyltransferase, and fructose-bisphosphate aldolase). These immunogenic proteins, which are encoded by genes that are reasonably conserved among SS9 strains, could be developed as vaccine candidates.