Use of enzyme-labeled antibodies to detect Salmonella in foods

An indirect enzyme-labeled antibody technique (ELAT), in which Salmonella typhimurium was used as a model, was developed as a method to detect Salmonella in food samples. A cellulose-acetate membrane filter, the matrix for detection, was placed on a membrane-filter base and overlaid with a multiwelled lucite template. Mixed broth enrichment cultures were dispensed in the template wells, and cells were spotted onto the membrane via suction. After fixation, the membranes were immersed in rabbit anti-S. typhimurium flagella antibody, washed, immersed in goat anti-rabbit antibody conjugated to peroxidase, and washed. Exposure of membranes to the substrates 3,3'-diaminobenzidine or benzidine resulted in development of brown or blue macroscopic reaction products, respectively, on spots containing S. typhimurium. ELAT results agreed with those of enrichment serology and cultural procedures on three food products containing known levels of S. typhimurium. Because of the magnification effect of the enzyme-substrate reaction, fewer cells were needed for detection than with enrichment serology, thereby reducing the total analysis time. The ability to test 14 or more samples simultaneously on a 47-mm membrane filter would facilitate screening large number of samples. Pending the development of a pure H antisera pool for the common Salmonella serotypes free from O antibodies, the ELAT demonstrated potential as a Salmonella detection methodology.