Shiga Toxin 1 (STX 1), ELISA, 96-test
The Shiga toxin 1 ELISA is an immunoassay for the qualitative screening of Shiga toxin 1 (Stx 1). The Shiga toxin 1 ELISA detects all known variants of Stx 1, including Stx 1a, 1c, 1d, and 1e. This test is suitable for the qualitative screening of Stx 1 in ground beef samples (please refer to the appropriate technical bulletins for additional matrices procedures). Shiga toxin is a virulence marker for O157 and non-O157 Shiga toxin producing Escherichia coli (STEC). The Shiga toxin 1 ELISA may be used as part of the United States Department of Agriculture Food Safety and Inspection Service (USDA FSIS) beef screening protocol described in the USDA FSIS Microbiological Laboratory Guidebook (MLG), chapters 5.08, 5A.04, and 5B.05. The test is an indirect ELISA based on the recognition of Shiga toxin 1 by specific antibodies. Ground beef samples are incubated with a medium that encourages E. coli growth, if present, and shiga toxin production. If Stx 1 is present in a sample, it is bound by an antibody immobilized on the wells of the microtiter plate. After a washing step, a second antibody is added which binds to the Stx 1 bound to the wells. A second washing step is followed by the addition of an HRP labeled antibody which binds to the existing antigen/antibody complex in the wells. After a final wash and addition of the substrate solution, a color signal is generated. The intensity of the blue color is proportional to the concentration of Stx 1 present in the sample. The color reaction is stopped after a specified time and the color is evaluated using an ELISA reader. The result of the evaluation is compared to a known value to determine whether the sample is positive or below the limit of Stx 1 detection.