Expression and immunogenicity of the sly gene of Streptococcus suis type 2

Abstract:

[Background] Streptococcus suis (SS) is an important zoonotic pathogen with 35 serotypes, of which the most serious is Streptococcus suis type 2 (SS2). Suilysin (SLY) secreted by various serotypes of SS may have a better immune protection. Therefore, SLY has a great advantage as a component of SS genetic engineering subunit vaccine. [Objective] to express the suilysin gene (sly) from a highly virulent strain (AH10-8) of SS2 in Anhui Province and to determine the immune protection of the SLY protein. [Methods] The full-length of sly was amplified by using a pair of specific primers with BamH I and Xho I sites. Subsequently, the PCR-amplified sly gene was cloned into the pET-30a vector. The plasmid was transformed into E. coli BL21 and expressed under the IPTG induced promoter. SLY was visualized by SDS-PAGE, and the protein antigenicity was confirmed by Western blotting. Zebrafish and Kunming mice were used to carry out SLY immune attack protection test, and the IgG antibody titer of serum in Kunming mice was detected by indirect ELISA, and the pathological changes and the protective rate were observed. [Results] The sly gene that cloned into pET-30a vector was highly expressed in E. coli BL21. The molecular weight of the SLY protein was about 60 kD and it is in accordance with the expected molecular weight of sly and SLY protein could react with serum from the SS2 infected patients. The serum antibody titers induced by the SLY protein and AH10-8 inactivated whole cells immune to IgG after three times were 1:6 400, 1:204 800 (ultrasound lysate of AH10-8 strain whole cell used as antigen) and 1:102 400, 1:51 200 (the SLY protein used as antigen). The relative protection rates of sly and AH10-8 inactivated total bacteria to Kunming mice and zebrafish were 40%, 80%, 84% and 92%, respectively. There was obvious difference between pathological changes in control group and experimental group. [Conclusion] The expressed SLY protein has a good reactivity and immunogenicity, which can induce a protective immune response. SLY protein can be a good candidate for the development of the SS2 vaccine.