Genetic Diversity Study On Virulence Markers Of Streptococcus Suis

Streptococcus suis is a major pathogen in porcine industry and also an important zoonotic agent causing severe invasive diseases in human. The virulence markers most frequently used were MRP, EF and Suilysion, and serotype 2 is the main serotype in many countries.Although there are many study on Streptococcus suis, which was also increase our knowledge of this pathogen, but we have not gain effective strategy to contral it. So it is nessary to study in novel point. In this paper we studied the genetic diversity of MRP, EF and SLY, then through these data we inspected the pan genome character, the ecological character and evolution character of Streptococcus suis. At last we discussed novel point on study and contral of Streptococcus suis.First, we studied the genetic diversity of MRP, EF and SLYwithin 180 Streptococcus suis serotype 2 field isolates, then characterized the association between genotypes and pathogenicity and detected selection pressure on these virulence-associated genes. It seemed that the whole ORF of mrp or epf was lost in the corresponding chromosomal region in some isolates. There were 3 main genotypes of these proteins in the isolates. The genotype of MRP was various, but genotype of 5LY&EF could be thought to be only two:sly+epf+sometimes sly+epf*) and sly0epf0, which also correspond to virulence and the phylogenetic relationship of these isolates. There was no significant positive selection pressure in the genes of the 3 virulence-associated factors. Compared with PCR method, sequencing the genetic locus of virulence-associated genes gave us more information of Streptococcus suis especially information on genetic diversity and interaction between these genes and host.Second, we studied genetic diversity of MRP, EF and SLY within 50 strains of different serotypes. It was found that the corresponding chromosomal region of MRP could be divided into 12 types and the corresponding chromosomal region of EF could be divided into 7 types. Our results suggested these variations resulted from integration of foreign genes and vestiges of genetic exchange such as insertion sequences and poly G were also found in some sequences. It was found that distribution of genotype of different virulence markers correspond to the phylogenetic ship of strains and the the Streptococcus suis population could be divided into 4 clusters.Through study on another 90 isolates, there was significant association between popilations and sources, which suggested the existence of the variations of mrp and epf was associated with ecological niche of Streptococcus suis. Taken together, these data suggested that:heterogeneity was an important feature of Streptococcus suis genome and different types of variations led to the phenomenon that mrp or epf was not detected in some strains; These variations resulted from integration of foreign genes and the mechanism might be various; the acquisition of these variations (genetic recombination or accumulation of mutation) were not random but impacted by ecological niches of S. suis.Through the study above it was found that the pan genome of Streptococcus suis had the general character of bacterial pan genome. It was also found that one gene might have different vatiatons in pan genome of Streptococcus suis, which would was mainly result of integration of foreign genes and the mechanism might also various. This fact increased the difficulty in study of Strptococcus suis. It was also found that these variations correspond to the phylogenetic relationship of the strains and was significant associated with sources of the strains. So it was recommendated that populations of Streptococcus suis was divided in to 3 ecotypes:pneumonic, systemic and commensalismic, and studied separately, which would decrease the interference of heterogeneity of Streptococcus suis genome in our future study. Our data suggested the pathogenicity of Streptococcus suis incolved many factors, and it was thought the genes crucial for bacterial adaption was in accessory genome (specializational genome). So is was recommendated that we first made clear the content of specializational genome, then gained the interaction network based on these genes, last formed targed strategy to contral Streptococcus suis.