Streptococcus suis, particularly serotype 2, is a human and porcine pathogen associated with a wide range of diseases including meningitis, septicaemia, and endocarditis. Among the genes in the capsular polysaccharide biosynthesis (cps) locus, cps2J exists only in the serotype 2 and 1/2 strains; therefore, cps2J-positive strains are suspected to have capsules of serotype 2 or 1/2. Coagglutination using anti-serotype 1 and 2 sera or transmission electron microscopy analysis of cps2J-positive isolates from pigs showed that all isolates from animals with meningitis were encapsulated, whereas 34% of isolates from animals with endocarditis were unencapsulated, indicating that capsule loss often occurred in the isolates associated with endocarditis. Some of the unencapsulated isolates had deletions and insertions at cps loci. In addition, a representative unencapsulated isolate and an unencapsulated strain showed adherence to porcine and human platelets, a major virulence determinant for infective endocarditis, to a significantly greater extent than the encapsulated strains. Although the capsule is considered an important virulence factor in S. suis, these results suggest that loss of capsular production is beneficial to S. suis in the course of infective endocarditis.
(Bacterial and Parasitic Disease Research Division)
Lakkitjaroen N. et al (2011) J. Med. Microbiol. 60:1669-1676