Interactions between Streptococcus suis serotype 2 and different epithelial cell lines.

Streptococcus suis is an important swine pathogen responsible for cases of sudden death, septicaemia, meningitis, endocarditis and pneumonia. It is also recognized as a zoonotic agent in people occupationally exposed to pigs or pig products. Knowledge on virulence factors of S. suis serotype 2 is limited and the pathogenesis of the infection is poorly understood. It has been suggested that the disease due to S. suis serotype 2 begins with colonization of the nasopharyngeal epithelium, followed by either spread within the respiratory tract or invasion of the bloodstream. The mechanisms involved in the access of bacteria from the bloodstream to the central nervous system are unknown. It is possible that epithelial cells of the choroid plexus also play an important role in the pathogenesis of the meningitis. Different interactions (adhesion, invasion and toxic effects) of S. suis serotype 2 with epithelial cell lines [LLC-PK1, PK(15), A549, HeLa and MDCK] were studied and compared to those of a human pathogen which also causes meningitis, group B Streptococcus (GBS). The results showed that S. suis serotype 2, in contrast to GBS, is able to adhere to but not to invade epithelial cells. The adhesin(s) involved seem(s) to be partially masked by the capsule and are a part of the cell wall. The haemolysin produced by S. suis serotype 2 is responsible for a toxic effect observed on epithelial cells. The results described give additional evidence that pathogenesis of the infection differs between S. suis and GBS. In particular, it is possible that suilysin-positive S. suis strains use adherence and cell injury, as opposed to direct cellular invasion, as part of a complicated multistep process which leads to bacteraemia and meningitis in pigs.