Non-O157 STEC Chromogenic Plating Medium

Presumptive positive colonies of non-O157 STEC appear as blue-black/gray domed colonies 1.0-2.5 mm in diameter with and without a clear ring and precipitate after 18-24 h at 41-42°C. Only one non-STEC strain (O103) grew as clear-white colonies 1.5-2.0 mm in diameter. Generic Escherichia coli, E. coli O104:H21 and some strains of Shigella will grow as blue-black/gray colonies 1.5-2.0 mm in diameter with and without a clear ring and precipitate. Other enterics will produce clear, white, green or yellow colonies 1.0-2.0 mm with and without a precipitate. The Gram (+)s and pseudomonad type bacteria are inhibited.

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Mechanism

Our medium uses the chromogen, X-β-D-glucuronic acid, sodium salt, to detect the enzyme, β-glucuronidase which is producted by 95-98% of E. coli strains as well as some Shigella, 20-30% of the Salmonella strains and about approximately 10% of the Yersinia sp. With the addition of cellobiose and myo-inositol coupled with the pH indicator, phenol red, some of the Salmonella and Shigella strains (producing green colonies) are differentiated from E. coli. Bile salts #3/sodium lauryl sulfate eliminates Gram positive bacteria, whereas, sodium cefsulodin inhibits pseudomonad type bacteria which can be the dominate organism in aerobically refrigerated fresh meat. Yersinia species are inhibited by sodium novobiocin. After incubation at 41-42°C for 18-24 hours, the non-O157 STEC strains (as well as all generic E. coli) produce blue-black/gray colonies, 1.0-2.5 mm in diameter with and without a clear ring and precipitate. Other bacteria that grow on the medium produce green, yellow and white/clear colonies.

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Industry Types

Beef, poultry (packers and processors) and fresh produce and environmental sources including drinking water and soils.

See Product Brochure, Use Protocol, SDS, Certificate of Analysis and Medium Preparation for more information about our medium.

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Advantages/Benefits

1. All of the non-O157 STEC strains have the same colony morphology eliminating confusion with serogroup type versus colony description.

2. To eliminate the false positives (generic E. coli and some Shigella strains) from the 6 major non-O157 serogroups, use a simple latex agglutination test.

3. Additional non-O157 STEC serogroups will have the same colony morphologies allowing this medium to be flexible for future STEC additions.

4. Highly selective/differential based on the β-glucuronidase reaction and 2 carbohydrate fermentations coupled with a pH indicator with a sensitivity of nearly 99% (69 non-O157 STEC strains tested).

5. Inhibits the growth of pseudomonad type bacteria which can be the dominate organism in aerobically refrigerated fresh meat.

6. Water insoluble chromogenic lattice prevents the colony color from diffusing into the agar making detection and enumeration much easier.

7. The shelf life of prepared plates remains stable for at least 60 days, stored in the dark at 2-8°C. One bottle of plating medium powder and one box of supplements will make approximately 330 plates.

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Ordering Information

M-1750

R & F® non-O157 STEC Chromogenic Detection System (350 g Bottle of Powder & one Supplement Box – Makes 320-340 Plates)

M-1700

R & F® non-O157 STEC Chromogenic Plating Medium (350 g Bottle)

M-1710

R & F® non-O157 STEC Supplement for Plating Medium (1 Box)

M-1760

R & F® non-O157 STEC Chromogenic Prepared Plate (Minimum Order of 20 Plates – Shelf life is 60 Days)