The invention relates to Streptococcus suis infection in pigs, vaccines directed against those infections and tests for diagnosing Streptococcus suis infections. The invention provides an isolated or recombinant nucleic acid encoding a capsular gene cluster of Streptococcus suis or a gene or gene fragment derived thereof. The invention further provides a nucleic acid probe or primer allowing species or serotype-specific detection of Streptococcus suis. The invention also provides a Streptococcus suis antigen and vaccine derived thereof.