An improved immunofluorescent-antibody (FA) method for the detection of salmonellae in foods and feeds was developed. This FA method combines a rapid cultural phase and a serological phase that allow for propagation of salmonellae in a minimum time, employing the industrial 8-hr work day as a guide. Two hundred fifty naturally contaminated human food and animal feed samples, representing 647 trials, were tested by the FA method. A total of 18 different food and feed samples was used. The method used by the Association of Official Analytical Chemists (AOAC) for the detection of salmonellae was the control method. The percent agreement when comparing the FA slide method to the AOAC method ranged from 87.1 to 95.3%, depending upon the conjugated antisera used in comparative studies.
A comparison of various cultural methods for use with microcolony and direct fluorescent-antibody (FA) techniques to detect salmonella was conducted using 102 naturally contaminated samples. The methods were: (a) a 27-h microcolony technique, (b) a 51-h selenite-F FA microcolony technique, (c) a 51-h tetrathionate brilliant green FA microcolony technique, and (d) a 53-h FA technique from a broth enrichment. All were compared to an F.D.A. approved modification of the AOAC method. The 51-h FA microcolony technique, which employed tetrathionate brilliant green broth and brilliant green agar plates, produced 4.9% false-positives and no false-negatives, and produced the greatest frequency of salmonellae detection.
The increased microbiological surveillance of foods by government regulatory agencies and industry has shown that salmonellae are an important cause of food-borne disease. The significance of salmonellae in food-borne disease has made it mandatory for regulatory agencies as well as industry to develop a rapid, reliable, and reproducible method for the recovery of salmonellae in feeds and foods.
Standard cultural procedures have become increasingly sensitive but not without a proportional increase in the time necessary for salmonellae detection and confirmation. This test may require from 5 to 7 days elapsed time with all of the implied disadvantages.
One of the most promising areas of activity is the rapid microbiological-serological technique employing an improved fluorescent-antibody procedure. While much has been done by the medical technologist, the application of this technique is relatively new in food microbiology. The published data show the method to be highly promising and possibly even more sensitive than the standard cultural procedure.
This technique is not without its inherent problems. Like all methods under investigation, there are differences in procedure, validity, and interpretation of the data. These are cited, with a description and critique of the work done, in order to give the reader an opportunity to evaluate the state of the art.
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