Screening of Trivalent Inactivated Vaccine Candidate Strains of Streptococcus suis Serotype 2,3 and 9 Using Galleria mellonella and Mice Infection Models
The aim was to evaluate the immune protective effect of a trivalent inactivated vaccine prepared from virulent strains of clinically isolated Streptococcus suis serotype 2,3 and 9 on mice.One virulent strain each of S.suis serotype 2,3 and 9 were screened from clinical isolates using Galleria mellonella and mice infection models(SS1803,SS1803024,SS1696),and the growth curves and virulence genes were tested.The strains were separately inactivated and mixed inactivated and mixed with adjuvants.4 × 107 CFU,8 × 107 CFU SS1803,2 × 108 CFU,5× 108 CFU SS1803024,1 × 108 CFU,5×108 CFU SS1696,and trivalent inactivated vaccine(2× 107 CFU SS1803+1.5 × 108 CFU SS1803024+3 × 107 CFU SS1696)were used to immune the BALB/c mice in two rounds,serum was collected to detect the levels of specific antibodies and the immune protection rates of the mice were observed after challenge with lethal doses of the three strains respectively.Then,a sub-lethal dose were used to challenge the trivalent immunized group,the bacterial loads in blood,brain,lung and spleen and the levels of cytokines IL-6 andIL-12 of mice were measured,and the histopathological changes in brain,lung,spleen and kidney were also observed.The virulence genes of the three vaccine candidate strains were identified as:SS1803:gapdh+/sly+/fbps+/orf2+/mrp-/89K-/gdh+/epf+,SS1803024:gapdh+/sly+/fbps+/orf2+/mrp-/89K-/gdh+/epf-,SS1696:gapdh+/sly-/fbps+/orf2+/mrp-/89K-/gdh+/epf-.Both monovalent and trivalent vaccine immune groups induced IgG antibodies corresponding to the immunized serotypes,with the production of IgG1 antibodies predominating.The trivalent group provided 83.3％,66.7％and 66.7％protection against serotype 2,3 and 9 strains,respectively.It also effectively reduced the bacterial loads in the tissues,and reduced the levels of serum inflammatory factors and the degree of tissue lesions of mice after infection.In this study,highly virulent strains of serotype 2,3 and 9 with high clinical prevalence were screened.Trivalent inactivated vaccine were prepared,which provided good immune protection in mice challenge model.These studies provided new materials for the development of multivalent vaccine of Streptococcus suis.
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维普
