Phylogenetic analysis of three key genes in Streptococcus. (A) Phylogenetic relationships of most Streptococcus spp. based on a 552-bp segment of the cpn60 gene. The tree was constructed with the MEGA (v.5.0.3) software package using the neighbor-joining method, with P-distance, complete gap deletion, and bootstrapping (n = 500) parameters. Accession numbers for sequences used in this analysis are shown after the strain names. The cpn60 segments of S. suis strains are highlighted with red branches, and the red type indicates the cpn60 segment from S. suis serotype Chz. The cpn60 segments of previous S. suis serotypes 32 and 34 and S. orisratti are highlighted with blue branches and red type. (B) Phylogenetic relationships of 35 serotypes of S. suis based on a 1,056-bp segment of the recN gene. The red type indicates the recN segment from S. suis serotype Chz. The recN segments of previous S. suis serotypes 20, 22, 26, and 33 are highlighted with blue branches and type. (C) Phylogenetic relationships of 35 serotypes of S. suis based on a 409-bp segment of the sodA gene. The red type indicates the sodA segment from S. suis serotype Chz. The sodA segments of S. suis serotypes 20, 22, 26, and 33 are highlighted with blue branches and type.