Fig. 6

Evaluation of immune responses and protection against S. Choleraesuis. a Scheme of immunization regimen. b Antibody responses induced by OMVs derived from C78-3, ΔtolA, ΔtolB, and ΔtolR strains. IgG titers against OMPs from C78-3 and three mutants groups were remarkably higher in contrast to the PBS group. c Survival of the mice subjected to immunization with OMVs obtained from C78-3, ΔtolA, ΔtolB, and ΔtolR strains. Intraperitoneal immunizations of PBS served as the negative controls. Two weeks posterior to the reinforce immunizations, all animals were challenged with the wild-type S. Choleraesuis. The infected mice were supervised every day for 30 days. *P < 0.05; **P < 0.01; ***P < 0.001