Immunization with a nontoxic mutant of staphylococcal enterotoxin A, SEAD227A, protects against enterotoxin-induced emesis in house musk shrews.

BACKGROUND Staphylococcal enterotoxins (SEs) are the most common cause of foodborne diseases and toxic shock throughout the world. However, no vaccine that prevents emesis induced by SEs has been described. METHODS A nontoxic mutant of SEA, SEAD227A, was constructed by site-directed mutagenesis and was purified by means of the Escherichia coli expression system. House musk shrews, a small emetic animal model, were immunized with SEAD227A and then challenged with wild-type SEA. SEA-induced emesis was recorded for 3 h. Antibody production was analyzed by gel double-immunodiffusion assay. Neutralizing activities of the antibodies with respect to superantigenic and emetic activities were analyzed in vitro and in vivo. RESULTS SEAD227A was devoid of both superantigenic and emetic activities but still retained its immunological activity. Immunization with SEAD227A strongly induced specific antibody production and provided significant protection against SEA-induced emesis. Antibodies from immunized shrews markedly inhibited the SEA-induced proliferation of spleen cells and also significantly ablated SEA-induced vomiting in the animals. CONCLUSIONS These results suggest that vaccination with SEAD227A, which is devoid of toxic properties, provides protection against SEA-induced emesis. This nontoxic mutant and its specific antibodies might be useful in the prevention and treatment of staphylococcal food poisoning.