Study on preparation of a Streptococcus suis ghost vaccine

Streptococcus suis (S.suis)is an important zoonotic pathogen in pigs and human. Bacterial ghosts (BGs) which are empty envelopes were used recently as efficient delivery system in vaccine development. In this study, S.suis ghosts were prepared and protective efficacy was evaluated in mice. Sodium hydroxide was used to prepare S.suis ghosts which were visualized under scanning electron microscopy. The optimum concentration of is Sodium hydroxide 6 mg/mL for ghosts formed. To investigate the S.suis ghosts as a candidate vaccine, the 50 BALB/c mice were randomly divided into three groups: Group A (control group), group B (subcutaneous injection of inactivated S.suis 2), group C (subcutaneous injection of inactivated S.suis 9), group D (subcutaneous injection of S.suis 2 ghosts), group E (subcutaneous injection of S.suis 9 ghosts). Serum were collected from five groups on the day of 7, 14, 21 and 28 after the first immunization for potency assay. Indirect ELISA results showed that antibody titer of blood serum of mice from group S.suis2 ghosts and group S.suis9 ghosts were significantly higher than blank group(P < 0.01), but were approximate to the conventional inactivated vaccine group SS2. In comparison with the conventional inactivated vaccine, S.suis ghosts as candidate vaccine strategy showed the excellent immunogenicity and provided protection against S.suis challenge in mice model.