The cps genes of Streptococcus suis serotypes 1, 2, and 9: development of rapid serotype-specific PCR assays.

We developed three type-specific PCR assays for the rapid and sensitive detection of Streptococcus suis serotype 1 (plus 14), serotype 2 (plus 1/2), and serotype 9 strains in tonsillar specimens from pigs. The PCR primers were based on the sequences of type-specific capsular genes of S. suis serotype 1, 2, and 9 strains. We recently characterized a major part of the capsular biosynthesis (cps) locus of S. suis serotype 2. Here we extended these studies and characterized major parts of the cps loci of S. suis serotypes 1 and 9. Type-specific genes were identified by cross-hybridization experiments between the individual cps genes and chromosomal DNAs from the 35 different serotypes. Four genes of S. suis serotype 1 specifically hybridized with serotype 1 and 14 strains only. Five genes of S. suis serotype 2 specifically hybridized with serotype 2 and 1/2 strains only, and two genes of S. suis serotype 9 specifically hybridized with serotype 9 strains. Until now rapid and sensitive diagnostic tests were available only for pathogenic strains of serotype 2 and highly pathogenic strains of serotype 1. The serotype-specific PCR assays can therefore be useful tools for the identification of serotype 1, 14, 2, 1/2, and 9 strains both for diagnostic purposes and in epidemiological and transmission studies. Therefore, these tests may facilitate control and eradication programs.