Improved immunological membrane filter method for detection of food-borne Salmonella strains

An improved membrane filter method that involves the use of an enzyme-labeled antibody stain has been developed for the rapid detection of Salmonella species in foods. The procedure is carried out directly on a hydrophobic grid-membrane filter without requiring transfer by blotting to nitrocellulose. Pure cultures of 54 Salmonella species and 10 foods artificially contaminated with Salmonella colindale gave a positive reaction in which Salmonella colonies were visible as purple dots. Of 11 nonsalmonella organisms, only Citrobacter freundii reacted with Spicer-Edwards antiserum. Of 22 naturally contaminated food samples, 10 were positive for both the hydrophobic grid-membrane filter procedure of the Association of Official Analytical Chemists and the improved enzyme-labeled antibody stain method, and there was perfect agreement between the methods. Of these 10 positive samples, one was negative by the Health Protection Branch method; of the negative samples, two were positive by this latter method. The improved enzyme-labeled antibody stain method allows detection of Salmonella spp. in foods within 48 h, requires little equipment, and is inexpensive, easy to perform, and suitable for automated detection.