Identification And Regulation Of Expression Of Virulence Factor Genes In Streptococcus Suis Serotype 2

The streptococcus suis serotype 2 strains cvcc606 and cvcc607 were used in our study. The strain cvcc606 was separated from swine in shanghai china, and the stains cvcc607 was separated in Japan.First of all, we studied the modality, characteristic of growth, hemolysis of streptococcus suis serotype 2, and we drew the growth curves in various condition. Laboratory result: the characteristics growth of strains cvcc606 and cvcc607 were similar, but hemolysis of tow strains were different. The growth curves were alike in the same condition, and the changes of growth curves were concurrent in the various condition. The result indicated that tow strains from different area were identical in many characteristics of growth.The different growth curves of streptococcus suis serotype 2 in our study show that temperature influence the growth of two strains. And gas exchange didn't influence the growth of two strains.We examined whether strains cvcc606 and cvcc607 had seven genes of virulence factors. The virulence factors included capsular polysaccharide (cps2j), muramidase released protein (mrp), extracellular factor protein(epf), haemolysin(sly), unkown gene(orf2), hyaluronate lyase (hly) and serum opacity factor(ofs). And we get the sequences of the genes. Laboratory result: the strains cvcc606 and cvcc607 had the seven genes of virulence factors. These virulence gene sequences of strains cvcc606 and cvcc607 were similar to the gene sequences of other streptococcus suis strains. Getting the gene sequence of serum opacity factor of strain cvcc606 was significant, because it mean that the strains separated from our country had the virulence factor. The ofs gene sequence of strain cvcc606 and the ofs gene sequence of foreign strain were same, and the ofs gene sequence of cvcc607 was high similar to foreign strain. Hly gene of strains cvcc606 and cvcc607 contains a frame shift resulting in a premature stop codon. This resulted in expression and secretion of a non-functional polypeptide that does possess hyaluronidase activity. The hly coder sequences of two strains were high similar to other streptococcus suis serotype 2 strains and were low similar to other serotypes strains. We found the expression of seven virulence factor of the same that streptococcus suis serotype 2 strain were different in our study. In conventional growth condition, virulence factors hly, orf2 and ofs were highly expressed and cps2j and sly were lowly expressed. And we tested the influence of temperature, CO2, still growth and shaken growth on the expression of seven virulence factor by RT-PCR. The results showed that the expression of some virulence factors from streptococcus suis serotype 2 was affected by temperature and gas exchange in the media. Laboratory result: from 37℃to 25℃, the expression of sly increased, and the expression of ofs diminished at 25℃. The results showed low temperature advanced the expression of sly and restrained the expression of ofs. The expression of hly and ofs diminished when the strain cvcc606 in shaken growth condition. The expression of mrp and sly increased, and the expression of hly and ofs diminished in the gas condition of air+20%CO₂. This result showed high content of oxygen restrained the expression of hly and ofs. High content of carbon dioxide restrained the expression of hly and ofs, and advanced the expression of mrp and sly.These results of our study are significative with cultivating streptococcus suis serotype 2 invitro and research of pathogenesis, and prevention and cure illness induced by streptococcus suis serotype 2.