| Streptococcus suis is a common pathogen in swine farms worldwide and is associated with a variety of diseases such as meningitis, arthritis, bronchopneumonia, and septicemia in piglets. It is also recognized as a zoonotic agent in humans especially those occupationally exposed to pigs or swine byproducts. Based on the capsular type,35 serotypes of S. suis have been described, and they are designated from 1 to 34 and 1/2. While S. suis serotype 2 (SS2) is the most widely isolated serotype, S. suis serotype 9 (SS9) is also a prevalent serotype that is frequently isolated from diseased pigs in countries such as Australia, Holland, Belgium, and Germany. Several epidemiological studies have reported that SS9 is also frequently isolated from the organs of diseased pigs in China. Furthermore, these studies have indicated that the prevalence of SS9 has increased during the last few years.1 Comparative proteome analysis of secreted proteins of ss9 isolates from diseased and healthy pigsInvestigations of virulence factors have focused on SS2. Unlike SS2, little is known about virulence factors for SS9. The two SS9 strains, GZ0565 and SH040917, were isolated from a diseased pig and a healthy pig, respectively. The virulence of these two SS9 strains was evaluated in zebrafish. The 50% lethal dose value of strain GZ0565 was 3.8×105 cfu/fish, while zebrafish injected with strain SH040917 exhibited no mortalities. For revealing proteins probably involved in different pathogenicity, a comparative proteomics approach was used to distinguish between the two-dimensional electrophoresis profiles of secreted proteins in two strains. With the use of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and MALDI-TOF/TOF-MS, protein spots that were unique to strain GZ0565 were identified, and led to the identification of 13 candidate proteins. The largest proportion of these proteins was metabolism-related. Five of the proteins are putative virulence-associated factors:DNA nuclease, o-acetylserine lyase, peptidoglycan-binding LysM, phosphoglycerate mutase, and putative 5'-nucleotidase. These findings contribute to the understanding of SS9 pathogenic mechanisms.2 Immunoproteomic assay of surface protein of SS9Studies on vaccine have focused on S. suis serotype 2 strains. However, little is known about immunogenic proteins for SS9. Therefore, an immunoproteomic-based approach was developed to identify immunogenic proteins of SS9. Cell wall proteins extracted from SS9 strain GZ0565 isolated from a diseased pig with meningitis were screened by two-dimensional Western blotting using anti-SS9 sera pooled from Specific Pathogen Free mice. Protein spots were excised from preparative gels and identified by MALDI-TOF-MS or MALDI-TOF-TOF-MS, which led to the identification of 8 immunogenic proteins (arginine deiminase, extracellular solute-binding protein, translation elongation factor Ts, neprilysin, peptide ABC transporter peptide-binding protein, pyruvate kinase, phosphate acetyltransferase, and fructose-bisphosphate aldolase). These immunogenic proteins, which are encoded by genes that are reasonably conserved among SS9 strains, could be developed as vaccine candidates.3 Identification of antigens common to SS2 and SS9 by immunoproteomic analysisIn addition to SS2, SS9 is another prevalent serotype, which is frequently isolated from the organs of diseased pigs in China. An immunoproteomic-based approach was developed to identify antigens common to SS2 and SS9 for vaccine development. Cell wall proteins extracted from SS2 strain HA9801 were screened by two-dimensional Western blotting using anti-SS2 sera, anti-SS9 sera, or pre-immune sera pooled from SPF mice. Protein spots on preparative gels were excised and identified by MALDI-TOF-MS, which led to the identification of four shared immunogenic proteins (arginine deiminase, translation elongation factor-Ts,1-phosphofructokinase, o-acetylserine lyase). The genes encoding these four proteins from SS9 strain GZ0565 were cloned and their proteins were overexpressed in E. coli. Western blot analysis of these recombinant proteins using the convalescent serum of an SPF mini-pig inoculated with the SS2 strain further confirmed the immunogenicity of these proteins. These immunogenic proteins, which are encoded by genes that are reasonably conserved among SS2 and SS9 strains, could be developed as vaccine candidates.4 Transcriptome profiling of zebrafish due to S. suis infectionLack of a common experimental infection model has hampered the studies on this bacterial species. Different research groups use different animal species, pigs with different ages and different immunological status, or different routes of infection. This may result in the important discrepancies regarding the virulence of even the same strain. Zebrafish as infection model for S. suis has been demonstrated by our groups, which has been cited by OIE. Here, an Affymetrix Zebrafish GeneChip was used to identify alterations in gene expression of zebrafish injected with SS2 strain HA9801. Among the 14900 transcripts in the microarray,189 genes were differentially expressed, of which 125 genes were upregulated and 64 genes were downregulated. Upregulated genes included many known components of the immune and inflammatory response, coagulation factors, complement activation and acute phase response, and stress and/or defense response. Three genes (encoding serum amyloid protein A, matrix metalloproteinase 9 and apoptosis-related cysteine protease), which have previously been implicated in the response to S. suis infection in other organisms, were also upregulated. Many of the genes we observed to be downregulated play roles in the positive regulation of locomotion or behavior, others are muscle specific. The reliability of the data obtained from the microarray was verified by performing quantitative real-time PCR on 12 representative genes. The data may provide further validation of this disease model, which will contribute to an understanding of S. suis pathogenic mechanisms.
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