Staphylococcus aureus · Confirmation
Toluidine Blue DNA Agar – thermostable nuclease test
Toluidine Blue DNA Agar is used for the detection of thermostable nuclease (TNase) of Staphylococcus aureus, a confirmation test for S. aureus in food.
- Thermostable nuclease test
- Pink zones around positive wells
- Confirmation of S. aureus
How Toluidine Blue DNA Agar works
Heated culture or extract is placed into wells in the agar. Thermostable nuclease of S. aureus hydrolyses the DNA, and the toluidine blue indicator shows the hydrolysis as a pink zone in the blue medium.
Typical results
| Result | Read-out |
| Positive (S. aureus) | Pink zone around the well |
| Negative | No colour change (blue) |
Technical data
| Preparation | 26.5 g/L; heat with stirring to boiling, autoclave 121 °C 15 min |
| Final pH | 9.0 ± 0.2 |
| Storage | Cool, dry place away from bright light; keep the container tightly closed |
| Shelf life | 3 years |
Applications and practical notes
Staphylococcus aureus and its thermostable nuclease are tested in food, for example in dairy, meat and ready-to-eat products. Typical applications include:
- Milk, cheese and dairy products
- Meat and ready-to-eat foods
- Confirmation of typical colonies
- Food-poisoning investigations
Working with Toluidine Blue DNA Agar: Heat the broth culture in a boiling water bath before testing, so that only the heat-stable nuclease of S. aureus is detected.
Good practice with dehydrated media: keep the bottle tightly closed in a cool, dry place, weigh the powder quickly to avoid moisture uptake, and use fresh distilled or deionised water. Check the pH of each new batch after preparation and before use, and label prepared media with the date. Performance of each lot can be verified with reference strains according to ISO 11133, the standard for the preparation, production, storage and performance testing of culture media.
About the Staphylococcus aureus methods: coagulase-positive staphylococci in the food chain are counted on Baird-Parker Agar according to ISO 6888-1, and typical colonies are confirmed with the coagulase test. For low numbers, ISO 6888-3 uses an MPN technique with Giolitti-Cantoni Broth, and the FDA BAM Chapter 12 describes direct plating and an MPN method with Tryptic Soy Broth containing 10 % NaCl. In pharmaceutical microbiology, the test for S. aureus in EP 2.6.13 and USP <62> uses Mannitol Salt Agar. COLO.Science offers media, supplements, rapid tests, identification kits and QC strains for every step.
Complete sets from one supplier: COLO.Science supplies culture media, supplements, rapid tests, identification kits and QC strains as complete sets for the method you follow. Send us your sample types and standards, and we will prepare an offer with the matching products and documentation.
Toluidine Blue DNA Agar is supplied by COLO.Science in the pack sizes listed under Ordering information. For larger quantities, regular deliveries or method-specific sets that include Toluidine Blue DNA Agar, please send us a request. With every delivery of Toluidine Blue DNA Agar you receive the lot number and expiry date, and on request we send the available documentation for Toluidine Blue DNA Agar.
Where Toluidine Blue DNA Agar fits in Staphylococcus aureus testing
- Colony count – Baird-Parker Agar with Egg Yolk Tellurite Emulsion (ISO 6888-1); alternatives: chromogenic S. aureus agar or Vogel-Johnson Agar
- Low numbers (MPN) – Giolitti-Cantoni Broth (ISO 6888-3) or Tryptic Soy Broth with 10 % NaCl (FDA BAM), then plating on Baird-Parker Agar
- Confirmation – coagulase test with Rabbit Plasma, latex kit or DNase Agar
- Pharmaceutical products – Mannitol Salt Agar for the S. aureus test of EP 2.6.13 / USP <62>; QC strains for media testing
See the complete Staphylococcus set in the Microbiology Catalogue →
Ordering information
| Product | COLO code | Pack |
|---|---|---|
| Toluidine Blue DNA Agar | PRO8181 | 500 g |
Product notice: preparation, storage conditions and shelf life are given on the label. Technical data on this page are for orientation; the label and the lot documentation apply. B2B prices are quoted net, excluding VAT.
Sales and technical support
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Quotations and technical support for culture media and microbiology products across our international sales territory. B2B prices are net, excluding VAT.
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Need the complete set for your method?
Send the sample type, target organism and the standard you follow. COLO.Science will put together the media, supplements, QC strains and confirmation tests for the whole procedure.
