Identification of Antigens Common to Streptococcus suis Serotypes 2 and 9 by Immunoproteomic Analysis

Abstract

Streptococcus suis is a Gram-positive pathogen that causes serious diseases in pigs. In addition to S. suis serotype 2 (SS2), S. suis serotype 9 (SS9) is another prevalent serotype, which is frequently isolated from the organs of diseased pigs in China. An immunoproteomic-based approach was developed to identify antigens common to SS2 and SS9 for vaccine development. Cell wall proteins extracted from SS2 strain HA9801 were screened by two-dimensional Western blot using anti-SS2 sera, anti-SS9 sera, or pre-immune sera pooled from specific pathogen free (SPF) mice. Protein spots on preparative gels were excised and identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometry, which led to the identification of four shared immunogenic proteins (arginine deiminase, translation elongation factor-Ts, o-acetylserine lyase, and 1-phosphofructokinase). The genes encoding these four proteins from SS9 strain GZ0565 were cloned and their proteins were overexpressed in Escherichia coli BL21. Western blot analysis of these recombinant proteins using the convalescent serum of an SPF mini-pig inoculated with the SS2 strain, anti-SS2 sera, and anti-SS9 sera pooled from SPF mice further confirmed the immunogenicity of these proteins. These immunogenic proteins, which are encoded by genes that are reasonably conserved among SS2 and SS9 strains, could be developed as vaccine candidates.

Keywords

• Streptococcus suis
• common antigen
• immunoproteomics