Immunogenicity and protective efficacy of recombinant alkaline shock protein 23 from Staphylococcus aureus in a murine model

The diversity and severity of infections caused and the rapid emergence of antibiotic resistance necessitates the development of a vaccine against Staphylococcus aureus. None of the antigens tried as vaccine candidates so far has been translated into a clinically viable vaccine. Recent research data suggest that antigens with the potential to activate cell mediated immunity along with humoral immunity would be the key to the development of a vaccine. Alkaline shock protein 23, a membrane-anchored protein involved in the stress response, has been identified as a CD4+ T cell antigen from S. aureus. In the present study, we report the evaluation of immunogenicity and protective efficacy of a recombinant alkaline shock protein 23 from S. aureus in mouse models. The gene coding for the protein was cloned and expressed in Escherichia coli, purified using immobilized metal iron affinity chromatography, sequence-confirmed using mass spectrometry and intraperitoneally administered to BALB/c mice. Serum titers of IgG, IgG1, and IgG2a in response to the protein were measured on post-immunization days 21, 35 and 42 using indirect ELISA and compared to control mice injected with PBS. Our results showed that the protein induced significantly higher (p < 0.01) antibody responses in immunized mice compared to the control mice. The mean serum antibody titers of IgG, IgG1 and IgG2a three weeks after the last immunization were found to be 25600, 25600 and 12800 respectively. Moreover, we found that immunization with Asp23 protected mice from a lethal dose of S. aureus strain USA300.