Bead-based DNA assay for the detection of Streptococcus suis in tonsillar specimens of pigs

Streptococcus suis is an important swine pathogen in nearly all countries with an extensive pig industry. In pigs it is associated with meningitis, arthritis, endocarditis, septicemia, pneumonia and sudden death. In certain parts of Asia S. suis is a common cause of bacterial meningitis in humans. Attempts to control S. suis in pig farming are hampered by the lack of sensitive diagnostic tools and effective vaccines. To provide a basis for adequate control measures, a bead-based suspension array was developed that targets six genes using multiplex PCR followed by target specific primer extension (TSPE) and subsequent hybridisation to beads. Assays were designed using AlleleID and Primer- Plex on consensus sequences of four serotype specific capsular polysaccharide (cps) genes (cps1I, cps2J, cps7H, cps9H), the extracellular virulence factor EF (epf) and a general S. suis marker (glutamate dehydrogenase; gdh). The proof-of-principle of the assay was demonstrated with chromosomal DNA of reference strains: each PCR was capable of producing the desired amplicon, also when performed in a sixplex reaction. Upon hybridisation of the TSPE products, all multiplex PCR products produced signals on the appropriate beads. This assay will be evaluated with field samples, using DNA isolated from tonsillar specimens of pigs. Ultimately, this expandable assay may be applicable for studying epidemiology and transmission, and could contribute to efforts aimed at control and eradication of S. suis in pig farming, thereby contributing to human health.