Porcine Streptococcus suis strains as potential sources of infections in humans: an underdiagnosed problem in North America?

S treptococcus suis is a gram-positive coccus, possessing cell wall antigenic determinants related to Lancefield group D, although it is genetically unrelated to other members of this group, such as enterococci. Streptococcus suis is a capsulated bacterium, with the composition of the capsule defining the serotype. There are presently 35 capsular types or serotypes. The original classification of S suis into Lancefield groups R, S, and T is erroneous, obsolete, and should be avoided. Strains of S suis originally defined as Lancefield groups R, S, and T correspond to capsular types 2, 1, and 15, respectively.1