Pathologic analysis of the brain from Streptococcus suis type 2 experimentally infected pigs.

Streptococcus suis type 2 (S. suis 2) is known as a major porcine pathogen worldwide and causes meningitis, septicemia, endocarditis, arthritis, and septic shock in pigs. Suilysin, a secreted protein of S. suis 2, is considered to be an important S. suis 2 virulence-associated factor. In this paper, the cerebellar lesions following experimental infection of pigs with S. suis 2 were studied. An immunohistochemical technique was applied to compare the distribution of bacteria and secreted suilysin protein in brain. The infected pigs developed histologic lesions of meningoencephalitis. Immunohistochemistry identified bacteria within the cytoplasm of neutrophils and macrophages localized in meningeal lesions. The secreted suilysin protein showed a similar localization within the cytoplasm of inflammatory cells, indicating that suilysin had high expression in vivo and may contribute to the pathogenesis of streptococcal meningoencephalitis.