Fluorescent-antibody technique in detection of salmonellae in animal feed and feed ingredients

Evaluation of a semiautomated system for direct fluorescent antibody detection of salmonellae

A semi-automatic system under development by Aerojet Medical and Biological Systems for the direct fluorescent antibody detection of salmonellae was evaluated with various food, feed, and environmental samples. All samples were simultaneously examined by Automated Bioassay System (ABS), manual direct fluorescent antibody procedures and cultural procedures. The ABS gave satisfactory results with the processed samples. It detected all of the culturally positive powdered egg and candy samples with no false-negative results and gave only 6.6 and 5.3% false-positive rates, respectively. With meatmeal samples the ABS failed to detect one culturally positive specimen that was also positive by manual fluorescent antibody and gave one (1.1%) false-positive result. A high rate of false-negative results was obtained by ABS on unprocessed samples of creek water, poultry, and sausage. Adding another enrichment step to the protocol reduced the false-negative rate considerably but severely increased the false-positive rate. The instruments worked reasonably well, but research is needed to improve enrichment procedures for samples to be processed by the system.

Factors influencing detection of salmonellae in rendered animal by-products

Detection of salmonellae in animal by-products is influenced by the enrichment and plating media and by quantity of product tested, and is related to the total plate count. A linear relationship exists between detection of salmonellae and total plate counts from 10(4) through 10(7) per gram.

Evaluation of the salmonellae fluoro-kit for fluorescent-antibody staining

An evaluation of the newly developed Clinical Sciences, Inc. Salmonellae Fluoro-Kit, which attempts to standardize the various aspects of the fluorescent-antibody (FA) procedure, was performed with 120 naturally contaminated human food, animal feed, and raw material samples. The Association of Official Analytical Chemists (AOAC) method for the detection of salmonellae was used as the control method. The Fluoro-Kit was found to be simple and conveniento to use. The results of this preliminary study show an industrially acceptable rate of recovery of salmonellae by using the Fluoro-Kit in comparison with the A.O.A.C. method. The Fluoro-Kit shows promise as a rapid, salmonellae FA screening method. Problems originally encountered in the application of the Fluoro-Kit are discussed. According to the manufacturer, strict adherence to the now revised procedures included in the Fluoro-Kit will control these problems.

Rapid, direct fluorescent-antibody method for the detection of salmonellae in food and feeds

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.

Rapid detection of Salmonella microcolonies by fluorescent antibody

A microcolony fluorescent-antibody (FA) procedure for detecting salmonellae was compared to the usual direct FA procedure on 304 environmental, food, and feed samples. The microcolony FA test detected all of the specimens found positive by culture, whereas the direct FA missed 3.1% of them. Both FA tests revealed stained organisms in some of the culturally negative specimens. The microcolony FA test has several advantages over the direct FA test: ease of examining the smears, elimination of the fluorescent background material, and increased sensitivity.

One-day fluorescent-antibody procedure for detecting salmonellae in frozen and dried foods

The indirect fluorescent-antibody technique was used to examine 422 food samples for the presence of salmonellae. A cultural phase involving a 16-hr preenrichment in buffered nutrient broth-milk medium followed by a 4- to 5-hr subculture into fresh medium of the same composition was evaluated. This procedure yielded a sufficient population of salmonellae so that no false-negative results were obtained. Of the 31 false-positives obtained, 12 samples yielded positive cultural results upon extensive subculture of the original enrichment broths. Yeast cells and both vegetative and spore forms of bacilli were observed to fluoresce when stained with anti-Salmonella serum. Efforts to ascertain the cause of these cross-reactions and several alternate explanations are discussed.