Characterization of Streptococcus suis isolates from the diseased pigs in China between 2003 and 2007

The aim of this study was to illustrate the characteristics of 407 strains of Streptococcus suis (S. suis) isolated from diseased pigs in China. The results revealed that S. suis, with 56.6% of the Streptococci isolates, had replaced Streptococcus equi subsp. zooepidemicus as the predominant agent. Among the strains investigated, serotype 2 (43.2%) was most prevalent, followed by serotypes 3 (14.7%) and 4, 8, 5, 7, 1/2 (3.2-6.4%). Serotype 2 was more frequently isolated from swine with systemic infection, while serotype 3 was significantly associated with pneumonia. A high percentage of S. suis serotype 2 strains (54%) belonged to the genotype sly+ mrp+ epf+, which is a highly virulent strain, as confirmed by mice infection test. Biofilm producers only had lowly virulence compared to strains with the same genotype, indicating that biofilm could be associated with virulence but be not the character of virulent strains. The present study contributes to understanding the characteristics of Streptococcus suis and controlling Streptococcal disease in China.