Studies Of Streptococcus Suis Type 2-Zebrafish Model And Prokaryotic Expression Of Major Histocompatibility Complex DXB Gene Exon 2 In Xiphophorus Helleri

This paper includes two parts of research: Study on Streptococcus suis type 2-Zebrafish Model; Prokaryotic Expression of Major Histocompatibility Complex DXB gene exon2 in Xiphophorus helleri.1. Streptococcus suis type 2-Zebrafish ModelZebrafish (Danio rerio) is a new infection model for studying mammal pathogens. 1 005 80-day-old AB line inbred zebrafish were grouped and infected intraperitoneally with 8 highly virulent strains for pigs (mrp+ef+). The 50% lethal dose(LD₅₀) were in the range of 5.36×10³cfu to 5.01×10⁴cful at 96 h. The SS2 strains which highly virulent for pigs also caused high morbidity and mortality in zebrafish. Acute septicemia were observed in inoculated fish. The bacteria inoculated could be reisolated from the organs of the fish. 1 strain avirulent for pigs (mrp - ef-) was also inoculated but not lethal for fish, and its LD50 was >10⁶ cfu. There is significant difference between the LD50 of SS2 virulent strains and avirulent one(p<0.01).Streptococcus suis type 2 HA9801 strain and ZY05719 strain were tested as vaccines against the virulent homologous and heterologous challenges in zebrafish. 200 Zebrafish(Danio rerio) were immunized and attacked intrapertoneally. 100 zebrafish were immunized with muramidase-released protein(MRP) subunit vaccine,and attacked with 50 LD₅₀HA9801 strain. 100 zebrafish were injected i.p. with positive swine anti-SS2 serum, inoculated with 50 LD₅₀HA9801 strain 24h after injected. The mortality and relative percent survival (RSP) were calculated. The RSP of HA9801 strain WBV are 78% against...