The Potential As A Live Attenuated Vaccine Of The Recombinant Of Streptococcus Equi Ssp. Zooepidemicus Expressing The Recombinant Immunogenic Protein Of Streptococcus Suis Type 2

Streptococcus suis （S. suis） is an important swine pathogen that causes many pathological conditions, such as arthritis, endocarditis, meningitis, pneumonia, and septicemia. Thirty-three serotypes （types 1/2 and 1 to 31,33） have been described based on capsular polysaccharides. Most S. suis strains isolated from diseased pigs belong to a capsular type 2（SS2）. SS2 is also an important zoonotic agent for people in contact with swine or their by-products and causes meningitis, permanent hearing loss, and septic shock.Streptococcus equi subsp. Zooepidemicus （SEZ） made lead to substantial economic losses for pig industry and became a substantial serous threat to human health especially whome involved in pig industry. It infects a wide range of animals, causing septicemia, meningitis, endocarditis, arthritis and mastitis. To date, the pig industry is still suffering from this disease in China.Though conventional inactivated vaccine has played a key role in protection against homologous bacteria infection, but the results were inconsistent when it was used to protect against heterologous bacteria infection. The study of novel genetically engineering vaccine would become the focus against the SS infection.To know the characteristics of Chinese popular strain SC19, a series of experiments were done for the goal of understanding this disease and the vaccinal study.For prevent SS2 and SEZ, in the present study, strain ST171 was used as a vector to express protective proteins of SS2. The recombinant strains ST171-MRP, ST171-SAO and ST171-HP0197 were constructed and its potential as a bivalent vaccine against both SEZ and SS2 infection was examined in mouse and pig model. The principal results were described as the following:1. The study of the characteristics of Chinese popular strain SC19A strain named SC19 was isolated from Sichuan province in 2005. SC19 was belong to SS2 and the genotype was mrp+epf+sly+. It has the haemolytic activity and could infect Balb/c, km, rabbit and pig.In this paper, the lesions following experimental infection of pigs with S. suis 2 were studied. The important clinical symptoms were nerval symptom and arthritis. Histopathologically, the infected pigs exhibited typical meningoencephalitis symptoms. Immunohistochemistry identified bacteria within the cytoplasm of neutrophils and macrophages localized in meningeal lesions. The brain is easy to be disoperation by the bacteria. The secreted suilysin protein showed a similar localization within the cytoplasm of inflammatory cells, indicating that suilysin had high expression by bacteria when the bateria went into in vivo of pig and may contribute to the pathogenesis of streptococcal meningoencephalitis.2. The potential as a live attenuated vaccine of the recombinant of streptococcus equi ssp.zooepidemicus expressing the recombinant immunogenic protein of streptococcus suis type 2In the present study, SEZ strain ST171, which is a live attenuated vaccine strain used widely in china for many years, was used as a source strain to develop a bivalent live vaccine. Muramidase-released protein （MRP）, surface protein SP1 （SAO）, hypothetical protein SSU98₀197 （HP0197） of SS2 which were proved to have the effective protetive efficacy were inserted into the genome of ST171 and gave rise to the recombinant strains ST171-MRP, ST171-SAO and ST171-HP0197. The proteins were expressed successfully in ST171-MRP, ST171-SAO and ST171-HP0197 as determined by western blot assay.The further protective efficacy of recombinant strains as live vaccine was evaluated in mouse and pig model. The inserted gene did not influence the virulence of strain ST171, and the 3 recombinant strains induced obvious SEZ-specific humoral immune responses and provided conspicuous protection against a lethal SEZ challenge, which is similar to vaccine ST171. Most importantly, the recombinant could induce detectable protein-specific IgG antibody and celular immunological response, and provide partial protect of mice against a lethal SS2 challenge. The further protective efficacy in pig model was done. The 2 recombinant strains ST171-SAO and ST171-HP0197, like ST171, induced obvious SEZ-specific humoral immune responses and provided conspicuous protection against a lethal SEZ challenge. Simultaneously, the recombinant strains could induce detectable protein-specific IgG antibody and celular immunological response, and provide partial protect of pig against a lethal SS2 challenge. These results indicate that ST171-MRP, ST171-SAO and ST171-HP0197 were the potential candidate for development of bivalent vaccine against both SEZ and SS2 infections.