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Objective: From the previous comparative genomic analysis, we found a specific unknown 10 kb sequence (including 11 Open reading Frames) in Chinese piscine strain GD201008-001 genome. To study the role of 10 kb in the pathogenicity of piscine S. agalactiae, the 10 kb sequence was deleted from the GD201008-001 genome., Methods: The isogenic mutant Δ10 kb was constructed by using the temperature-sensitive Streptococcus-E. coli shuttle vector pSET4s. We compared the growth characteristics, adherence to HEp-2 cell and bacterial virulence in a zebrafish infection model between wild strain and mutant. Meanwhile the expressions of the known virulence genes from GD201008-001 and Δ10 kb were also quantified by real-time PCR., Results: The Δ10 kb showed no significant differences in bacterial morphology and adherence to HEp-2 cells compared with the wild-type strain, but the speed of growth was slightly slower than the wild strain. Furthermore the 50% lethal dose of Δ10 kb was decreased up to 10-fold (P < 0.001) of the parental strain in a zebrafish infection model, and the expressions of the virulence genes, PI-2b and neul, were significantly increased in the mutant., Conclusion: These findings demonstrated that the 10 kb sequence of piscine Streptococcus agalactiae exerts a significant effect on bacterial virulence and probably regulates the virulence genes expression of GD20 1008-001.

Objective: We studied the serological response between the special regions on the Torque teno sus virus 2 (TTSuV2) ORF1 coded protein and the porcine sera from conventional pigs., Methods: Based on a Chinese TTSuV2 strain from Guangdong province, two overlapped virus proteins were expressed from Escherichia coli. Then, purified recombinant TTSuV2 ORF1a and TTSuV2 ORF1ab proteins were used as the antigens in the Western Blotting and ELISA assay., Results: The recombinant TTSuV2 ORF1a and TTSuV2 ORF1ab proteins were identified with the special tag monoclonal antibody. The results of the ELISA tests shown that there were significant relationships between two groups of dates from the recombinant TTSuV2 ORF1a and TTSuV2 ORF1ab proteins antigenic assay. The results of the following Western Blotting assay indicated that the TTSuV2-specific IgG antibodies were contained in pig sera., Conclusion: The truncated TTSuV2 ORF1a protein (positions 168 to 346 corresponding to TTSuV2 GDIMA1) contains important B cell epitopes which can stimulate immune system antibody secretion. The truncated TTSuV2 ORF1a protein could be effective in TTSuV2 immunodiagnosis.

Objective: There are one-way or two-way cross-reactions among Streptococcus suis serotype 1, 2, 1/2 and 14, the reason to which was unknown., Methods: 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 kDa and 512.72 kDa by high performance gel permeation chromatography, respectively., Results: 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, 2 14 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.

In recent years, mass outbreaks of highly pathogenic (HP) porcine reproductive and respiratory syndrome virus (PRRSV) have spread all over the Chinese swine industry. Based on the first infectious cDNA clone of HP PRRSV strain pJX143 and that of an attenuated PRRSV, pAPRRS, constructed in our group, we constructed several chimeric clones with various substitutions of structural protein genes (ORF4-7) and 3' UTR between attenuated pAPRRS and virulent pJX143.Upon transfection of MA-104 cultured cells, all chimeric constructs pSX12, p5NX12, and p56N12 were rescued. The rescued viruses maintained the similar virological properties, based on the results of the growth curve of the rescued viruses. To test if the chimeric viruses can be used as a vaccine candidate, vSX12 and v56N12 vaccinated pigs were challenged with the HP PRRSV JX143 strain. As a result, the vSX12 vaccinated pigs were all seroconverted by 14-day-post vaccination, while v56N12 vaccinated pigs showed poor antibody response. Upon challenge, the vSX12-vaccinated group showed no signs of clinical PRRS syndrome, and virema period was shorten to 6 days post-challenge. Our results demonstrated that 1) vSX12 chimeric virus is a good vaccine candidate; 2) the virulence determinants of HP PRRSV probably located in coding regions other than ORF3-7 and 3' UTR, as our chimeric viruses were proved to be attenuated.