Detection and analysis of Staphylococcal enterotoxin A in food by Western immunoblotting

Western blotting has the potential to overcome some of the major problems associated with enzyme-linked immunosorbent assay (ELISA) detection of toxins in food, such as cross-reactivity with unrelated antigens and insensitivity with heat-treated foods, because the Western procedure solubilizes denatured protein and allows characterization of the antigen that reacts with the antibody. A simple Western immunoblotting protocol was developed to identify and measure the level of Staphylococcus aureus enterotoxin A (SEA) in food. Test samples are merely homogenized with no additional solubilization or pretreatment steps. The immunoblots detect SEA at levels as low as 100 pg/ml. Using the simplified sample preparation, both native and heat-denatured SEA were identified in a variety of foods including mushrooms, milk, potato salad and meat products. Our data suggest that SEA is being secreted at mid-log growth in BHI media as well as in mushrooms. These results suggest that Western blotting is a useful tool for determining the presence of SEA in foods because it allows characterization of the antigen reacting with the antibody and can be used for heat-treated foods, thus overcoming some of the limitations of the ELISA test.