| Capsular polysaccharides are generally some mucous material surrounding the bacterial surface. Capsular polysaccharides paly an important role in infection and pathogenicity of Streptococcus suis. Acording to the antigenic differernce of the capsular polysaccharides, there are 33 serotypes of Streptococcus suis. The structure of the capsular polysaccharides in every serotype is different, which was composed of repeating oligosaccharides linked by glycosidic bond. The synthesis of the capsular polysaccharides is complex. The capsular polysaccharides synthesis locus encodes the enzymes to build the repeat unit, including glycosyltransferase, acetyltransferase, repeat-unit flippase, polymerase and so on. Research on the pattern and construction of the capsular polysaccharides synthesis locus (CPS locus) can provide the detailed knowledge to synthesis pathway and the reasons to the variation in capsular polysaccharides. The sequence of the capsular polysaccharides synthesis locus also can be used to screen the serotype-spesific genes and develop serotype-spesific detection method, which is convenient in generous clinical sample detection. The analysis associated with monosaccharide compositon can reval the reason to the cross-reaction among some serotypes.1. CLONING AND ANALYSIS OF THE CONSERVED REGIONS IN THE CAPSULAR POLYSACCHARIDES SYNTHESIS LOCUS OF STREPTOCOCCUS SUISBased on the CPS locus sequence of Streptococcus suis serotype 1,2,7 and 9 and the results to the cross-hybridization experiments, the CPS locus of Streptococcus suis was hypothesized as cassette-like structure which is similar to Streptococcus pneumoniae. PCR, sequencing and southern blotting was used to certify the hypothesis. The results showed that the CPS locus of Streptococcus suis was cassette-like structure. The 5’-end of the CPS locus contained 4 regulatory genes which is highly similar in all the serotypes. The flanking genes of the CPS locus are conservative. The flanking gene aroA, which is at the downstream to the CPS locus, was selected as the objective gene to develop the PCR to amplify the serotype-specific regions. The phylogenetic relationship of the orfY、orfX、cpsA、cpsB、cpsC、cpsD and aroA was analyzed in this part.2. GENETIC ANALYSIS OF THE CAPSULAR POLYSACCHARIDES SYNTHESIS LOCUS IN 15 STREPTOCOCCUS SUIS SEROTYPESCapsular polysaccharides synthesis locus of 14 Streptococcus suis serotypes (serotype 1,3,4,5,7,8,9,10,14,19,23,25 and 1/2) was sequenced and compared with that of serotype 2. The capsular polysaccharides synthesis locus of the above-mentioned 15 serotypes can mainly fall into 2 groups. The serotype-specific genes located in the central region, including glycosyltransferase, acyltransferase, phosphotransferases, aminotransferases, glycerol phosphotransferase, metalloprotease, pyruvyltransferase, polysaccharide polymerase and flippase. The 3’region encodes some IS transposase. In serotype 1,2,14,16 and 1/2, five proteins (NeuA,B,C,D and sialyltransferase) involved in sialic acid synthesis located at the downstream of the locus. All the translated proteins in the capsular polysaccharides synthesis locus were clustered into 127 homology groups by TribeMCL algorithm. General organization of the locus in 15 serotypes suggested that the capsular polysaccharide of Streptococcus suis could be synthesized by the Wzy-dependent pathway. The relationship of the locus in the 15 serotypes with immunologic cross-reaction and the mechanism to the generation of capsule diversity of Streptococcus suis was discussed.3. DEVELOPMENT AND APPLICATION OF THE PCR ASSAYS FOR RAPID DETACTION TO THE 9 SEROTYPES OF STREPTOCOCCUS SUISExcept serotype 1(14),2(1/2),7 and 9, only laborious and time-consuming antiserum agglutination methods can be used to identify other serotypes. Because of the increasing occurrence infected by different Streptococcus suis capsular types in pigs or human, it’s necessary to develope rapid diagnostic methods to deal with them. Based on the serotype-specific genes identified by cross-hybridization experiments, rapid PCR methods for detection to the 9 serotypes (3,4,5,8,10,16,19,23 and 25) were developed in this paper.One handrud and ninety nine chinses clinical isolates of Streptococcus suis were detected by these PCR methods. The PCR identification results were accordant to the traditional serum agglutination. The PCR assays can be used in detection not only in reference strains, but also clinical isolates. It also can identify some isolates which can’t be identified by antiserum agglutination. These assays will be a useful diagnostic tool to detect Streptococcus suis isolates and to identify their serotypes.4. COMPARISON TO THE MONOSACCHARIDE COMPOSITION OF CAPSULAR POLYSACCHARIDES IN STREPTOCOCCUS SUIS SEROTYPE 1, 2,14 AND 1/2There are one-way or two-way cross-reactions among Streptococcus suis serotype 1,2,1/2 and 14, the reason to which was unknown. The capsular polysaccharides of serotype 14 and 1/2 were purified on Sephacryl S-300 column and identified by phenol-sulphuric acid method and dot-ELISA. The molecular weight of the serotype 14 and 1/2 capsular polysaccharides was revealed as 487.38 kD and 512.72 kD by high performance gel permeation chromatography, respectively. The monosaccharide composition of serotype 14 and 1/2 capsular polysaccharides was determined as Glc/Gal/GlcNAc/Rha/Neu5Ac (1:2.94:1.35:0.24:0.37) and Glc/Gal/GlcNAc/GalNAc/Rha/Neu5Ac (1:1.67:1.05:0.93:0.72:0.7) by pre-column derivatization high performance liquid chromatography, fluorescent labeling HPLC and NMR, respectively. These were compared with the composition of serotype 1 and 2 capsular polysaccharides. Glc, GlcN, Gal and Neu5Ac was contained in the capsular polysaccharides of serotype 1,214 and 1/2. But there is no prominent correlation between the monosaccharide composition and cross-reactions. The cross-reactions among them could be induced by the structure of the capsular polysaccharides and/or the other components on the cell wall. |
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