Identification And Pathogenesis Study Of Streptococcus Suis Serotype 2 In Vivo Induced Antigen

Streptococcus suis is an important cause of meningitis, septicaemia, arthritis and sudden death in pigs. So far,35 serotypes were described based on variation of the capsular polysaccharide (CPS). S. suis infections especially the serotype 2, caused great economic loss in pig industry worldwide every year. Moreover, S. suis can infect humans, mainly associated with exposure to infected pigs or tissues. A recent outbreak in China caused by a serotype 2 strain resulted in 38 deaths among 215 infected humans, an 18% mortality rate. The bacterium has caused sporadic human illness in other countries as well, including the United Kingdom, and has been identified as a leading cause of bacterial meningitis in Hong Kong Special Administrative Region and Vietnam. S. suis infections raised considerable international concerns among the public health professionals.Currently, attempts to control the diseases caused by S. suis are still hampered by insufficient knowledge of pathogenesis mechanism, and a lack of effective vaccines and sensitive diagnostic methods. Althogh a set of virulence traits was identified. Knoledge about he molecular mechanism of invasion and damage of the host tissue by the bacteria is still limited. In order to put an insight to the interaction of host and pathogen, we use in vivo induced antigen technology to identify of Streptococcus suis serotype 2 antigens which were uniquely expressed during infection.1. Identification of Streptococcus suis antigenic determinants specifically expressed during infectionStreptococcus suis is an important swine and human pathogen with adhesive and invasive properties. Pathogenesis mechanism of S. suis infection has not been completely defined due to limited information on its virulence factors. In this study, in vivo antigen technology (IVIAT) was used to identify S. suis antigens expressed during pig infection. In total,20 in vivo induced (ivi) genes were identified, including suilysin, a known putative virulence factor; enzymes function in metabolism/housekeeping, cell division/replication and cell wall degradation, transporting related genes, cell wall-associated proteins, and hypothetical proteins of unknown function. Five genes were selected to test the in vivo expression by relative real-time PCR in mice. SecA, putative modification enzyme (mod), moeA and orf28 were apparently upregulated in vivo. Of the twenty ivi genes, three parts of a subtilisin-like serine protease (ssp) gene were identified. The three segments (sspN, sspM and sspC) were expressed and purified. The anti-SSP antibodies in various phages after infection were evaluated. It was found that the antibody developed as early as at the first week post infection. Such proteins might be explored as markers of S. suis infection. S. suis antigens identified by IVIAT warrant further evaluation on their contributions to pathogenesis, and may probably be developed for diagnostc and preventive applications.2. Identification of a cell wall-associated subtilisin-like serine protease involved in the pathogenesis of Streptococcus suis serotype 2Streptococcus suis is an important swine and human pathogen, and also an emerging zoonotic agent. A surface-associated subtilisin-like serine protease (SspA) of S. suis was identified by screening a genomic expression library as fragments of this protein reacted most strongly with convalescent-phase pig sera. The sspA gene is present in 29 of 33 S. suis serotypes reference strains and is expressed on the surface of S. suis. Relative real-time quantitive PCR assay demonstrated that sspA mRNA expression in vivo was several thousand fold of that in vitro. A sspA- mutant was generated from a S. suis serotype 2 strain SC19 by allelic exchange. The mutant was not different from the wild type strain in subcellular structures and in hemolytic phenotype. However, the virulence of the sspA mutant was markedly lower than the wild type in pigs as demonstrated in experimental infections. These data indicated that the surface associated protein SspA is a conserved virulence factor of S. suis and is involved in the pathogenesis of S. suis.