Immunological methods for detection of foodborne pathogens and their toxins

Improved methods to detect microorganisms and their toxins introduced during the last decade involve among others recombinant DNA techniques and various immuno-assays such as the enzyme-linked immunosorbent assay and the latex agglutination. Immuno-assays are based on a quantitative reaction of an antigen (bacterial metabolite, e.g., toxin) with its antibody. Therefore, they are suited for detection of microorganisms based on their production of specific antigens and for quantitative detection of bacterial toxins. Sensitivity and specificity of immuno-assays are mainly determined by the antiserum used. In this respect the use of well selected monoclonal antibodies can be of advantage. With the enzyme-linked immunosorbent assay and latex agglutination test quantities of 0.1-1 ng of antigen/ml can be detected. Of both techniques the latex agglutination method has several advantages; the method is simple, inexpensive and rapid. Since each immuno-assay is sensitive to non-specific reactions, recognition of false positive results is necessary. The most appropriate method for this is to add an inhibitor to the test sample which blocks specifically the paratope of the immunoglobulin. Another general disadvantage of immuno-assays is that only the antigenicity is determined and this may differ from the actual toxicity. Therefore, antibodies should be used that react with the toxic centre(s) of the molecule, which can be accomplished by using well selected monoclonal antibodies.