Salmonella is a genus of a facultative aerobic gram-negative flagellate bacteria which may be found in a variety of foodstuffs, dairy products, feed, water and wastewater, and which are a cause of various pathological conditions in man. Salmonellosis, a food-associated disease, is a major problem in the United States because of its incidence, economic significance, and hazardous nature. Salmonellosis is usually not a fatal disease, although some fatalities have been reported in infants and the aged.
Food, dairy and feed industries intensively scrutinize their products for Salmonella contamination because of the economic impact of recalling and destroying contaminated products and the potential loss of confidence by consumers concerning product safety.
Testing of products for Salmonella contamination is complicated due to the fact that the organism is commonly present in very low levels. Further complicating the task of detection of the Salmonella is the presence of numerous other microorganisms, including competitive flagellate species, typically present in foodstuffs and animal feeds, that can interfere with the cultural detection of the microorganism.
There are a number of disadvantages associated with the conventional detection procedures for Salmonella. The cultural procedures are cumbersome and labor-intensive to perform, require expensive laboratory materials, are lengthy (requiring up to four days to complete), and may yield false negative results. The fluorescent antibody technique requires highly trained personnel, expensive fluorescent microscopic systems, and costly fluorescein-labeled antisera, which at times lack specificity.
Several attempts have been made to devise other rapid and simple methods for the detection of Salmonella. Some of these methods involve preferential migration of Salmonella through a selective semi-solid motility medium. Mohit et al., in "A Simple Single-Step Immunoimmobilization Method for the Detection of Salmonella in the Presence of Large Numbers of Other Bacteria," J. Med. Microbiol., Vol. 8, page 173 (1975), and Swaminathan et al., in "Rapid Detection of Salmonella in Foods by Membrane Filter-Disc Immobilization Technique," J. Food Science, Vol. 43, No. 5, p. 144 (1978), describe selective semisolid media which promote the migration of Salmonella in a petri dish followed by immobilization using polyvalent H antisera. Swaminathan et al. used a membrane filter to concentrate Salmonella from the primary selective enrichment before selective migration in order to increase recovery.
Although these motility techniques showed promise, operational difficulties compromised their effectiveness. In particular, problems included:
(1) the lack of definite and easily interpretable reactions to indicate the presence of Salmonella;
(2) the use of chemical agents in the motility medium to promote the selective migration of Salmonella which greatly reduced or completely inhibited motility of certain Salmonella strains; and
(3) the use of intricate glassware arrangements which made setup and inoculation difficult and expensive.
Consequently, there is a need in the art for an improved method for detecting Salmonella or other particular motile organisms in a sample, which method (a) is sensitive and specific; (b) is rapid, microbiologically safe, relatively uncomplicated, and inexpensive; and (c) provides a definite and easily intepretable indication of the presence of Salmonella or the other particular motile organism to be detected. The present invention fulfills this need and further provides other related advantages.