Multiplex PCR assay for the detection of serotype 2 and 9 of Streptococcus suis

To develop a highly specific, sensitive and rapid method for the detection of Streptococcus suis with multiplex PCR, 4 pairs of primers were designed, in which 2 pairs of them were based on capsular polysaccharide genes specific for serotype 2 and 9 (cps2 and cps9), and the other 2 pairs of primers were based on the virulence genes epf and mrp, encoding the extracellular factor protein (EF) and muramidase released protein (MRP) of the virulent serotype 2 respectively. Ten strains of Streptococcus suis in which 5 strains belonged to serotype 9 and the other 5 strains belonged to serotype 2 were identified by means of the multiplex PCR assay with several strains of negative controls. It was found that of the 10 strains of S.suis, isolated from diseased pigs, all were positive by the multiplex PCR assay. The 5 strains of serotype 2 could be further divided into 2 genotypes, i.e.cps2~+mrp~+epf~+ (3 strains); cps~+mrp~-epf~-(2 strains). By using the same technique of multiplex PCR, no PCR product could be detected from S.suis group C and group D, ETEC O148, STEC O138, Staphylococcus and Salmonella enteritidis.The target strain of serotype of S.suis could be detected definitely when the template contained as few as 10 cfu. It is concluded that this multiplex PCR assay is a highly specific, sensitive and rapid method for the detection of serotype of S.suis.