Immunogenicity of Murein‐associated Proteins from Temperature‐stressed Streptococcus suis Cultures

We compared immunogenicity in pigs of whole cell lysate proteins (WCP) with murein-associated proteins (MAP) obtained from a virulent serotype 2 strain of Streptococcus (S.) suis grown at 32 or 42 degrees C. Protein fractions were tested for their ability to induce antibodies in 3-week-old piglets by enzyme-linked immunosorbent assay and Western blot analysis. We found a significant increase in the antibody levels in all sera irrespective of the preparation used for immunization. However, alpha-WCP sera showed higher reactivities than alpha-MAP sera, and piglets immunized with 32 degrees C preparations (alpha-32 sera) showed higher responses than those immunized with 42 degrees C preparations (alpha-42 sera). Western blot analysis revealed that alpha-WCP sera in part reacted with different proteins when compared with alpha-MAP sera. Furthermore, some proteins were only detected by alpha-32 but not by alpha-42 sera. In conclusion, the results demonstrate the immunogenicity of cell wall MAP of S. suis, and highlight the importance of considering growth conditions in the preparation of subunit vaccines.