Role Of A Two-Component Signal Transduction System 2148HK/RR In Pathogenicity Of Streptococcus Suis Type 2

To construct gene knock-out mutant of a two-component signal transduction system 2148hk/rr in Streptococcus suis type 2 virulent strain 05ZYH33.Recombinant gene knock-out vector was constructed consisting of the spc^r cassette with flanking homology regions to the target genes, the isogenic 2148hk/rr-deficient mutant was generated by allelic replacement. PCR analysis and Southern hybridization indicated that the coding genes of 2148hk/rr were replaced completely by the spc^r cassette. The mutant of 05ZYH33 2148hk/rr system was constructed successfully, which laid the foundation for further research on the role of this two-component signal transduction system during infection.Susceptivity of different strains of mice to the Streptococcus suis type 2 virulent strain 05ZYH33 were evaluated. Two groups of 28-day-old mice, 10 mice each, which belonged to BABL/c and ICR respectively, were inoculated intraperitoneally with 1mL volume of bacterial suspension corresponding to 5×10⁸ CFU of bacteria. All BABL/c mice died in 14 days while 6 of the ICR mice survived, suggesting BABL/c mice as a more susceptive strain to evaluating virulence of 05ZYH33. In order to determine the 50% lethal dose (LD₅₀) of the bacteria to BABL/c mice,30 mice were equally divided into 6 groups. The first 5 groups of mice were inoculated with 1 mL volume of bacterial suspension with 5 times' dilution, while the last group's mice with THS served as negative control. The calculated LD₅₀ turned out to be 8.4×10⁷ CFU.This study laid foundation for further research on pathogenesis of Streptococcus suis type 2.The pathogenic role of a two-component signal transduction system 2148hk/rr of Streptococcus suis type 2 were evaluated in murine and swine model respectively. In murine model, thirty BABL/c mice of 28-day-old were equally distributed into three groups. The first group's mice were inoculated intraperitoneally with 1mL volume of Streptococcus suis type 2 virulent bacterial suspension corresponding to 5×10⁸ CFU of bacteria,while the second group with its mutant strain which lacks the two-component system coding gene 2148hk/rr.The last group's mice were inoculated with equal volume of THS and served as negative control. All of the first group's mice died in 2 days while no mice died in the second group though some of the inoculated mice were infected slightly. In swine model, nine piglets of three-week-old were divided equally into three groups. The first and thesecond group's piglets were inoculated intravenously with 1mL volume 10⁸ CFU of the virulent and its mutant strain of Streptococcus suis respectively. The third group's piglets were inoculated with equal volume of PBS and served as negative control. All the animals belonged to the first two groups died in two days, while the last control group's animal were unaffected. The discrepant results we got from the two different animal model suggests a different role the two-component system played during infection of the pathogen to the different hosts. Further research needs to be done to get more details about the pathogenic role of this two-component system in Streptococcus suis type 2...