Generation of a Novel Staphylococcus aureus Ghost Vaccine and Examination of Its Immunogenicity against Virulent Challenge in Rats

Staphylococcus aureus is a Gram-positive pathogen that causes a wide range of infections in humans and animals. Bacterial ghosts are nonliving, empty cell envelopes and are well represented as novel vaccine candidates. In this study, we examined the immunogenicity and protective efficacy of S. aureus ghosts (SAGs) against a virulent challenge in rats. Nonliving SAGs were generated by using the MIC of sodium hydroxide. The formation of a transmembrane lysis tunnel structure in SAGs was visualized by scanning electron microscopy. To investigate these SAGs as a vaccine candidate, rats were divided into four groups, A (nonimmunized control), B (orally immunized), C (subcutaneously immunized), and D (intravenously immunized). The IgG antibody responses were significantly stronger in the SAG-immunized groups than in the nonimmunized control group (P < 0.05). Moreover, a significant increase in the populations of CD4(+) and CD8(+) T cells was observed in all three immunized groups (P < 0.05). We also found that serum bactericidal antibodies were significantly elicited in the SAG-immunized groups (P < 0.05). Most importantly, the bacterial loads in the immunized groups were significantly lower than those in the nonimmunized control group (P < 0.01). These results suggest that immunization with SAGs induces immune responses and provides protection against a virulent S. aureus challenge.