Resolution of Streptococcus suis Serotypes 1/2 versus 2 and 1 versus 14 by PCR-Restriction Fragment Length Polymorphism Method.

Streptococcus suis is an important pathogen of pigs but is also transmissible to humans, with potentially fatal consequences. Among 29 serotypes currently recognized, some are clinically and epidemiologically more important than others. This is particularly true for serotypes 2 and 14, which have a large impact on pig production and also on human health. Conventional PCR-based serotyping cannot distinguish between serotype 1/2 and serotype 2 or between serotype 1 and serotype 14. Although serotype 1/2 and serotype 2 have a very similar cps locus, they differ in a single-nucleotide substitution at nucleotide position 483 of the cpsK gene. Similarly, serotypes 1 and 14 have a very similar cps locus but also differ in the same nucleotide substitution of the cpsK gene. Fortunately, this cpsK 483G→C/T substitution can be detected by BstNI restriction endonuclease. A PCR-restriction fragment length polymorphism (RFLP) detection method amplifying a fragment of the cpsK gene digested by BstNI restriction endonuclease was developed and tested in reference strains of these serotypes and also in field isolates.