Staphylococcus aureus · Confirmation agar
DNase Agar – deoxyribonuclease test for staphylococci
DNase Agar is used to detect deoxyribonuclease activity, an additional test for the identification of Staphylococcus aureus and of other DNase-positive bacteria such as Serratia. The medium contains DNA, which is hydrolysed around positive colonies.
- Detects DNase activity of S. aureus
- Clear zone after flooding with 1 mol/L HCl
- Also usable with toluidine blue
How DNase Agar works
Colonies are spot-inoculated and incubated. The plate is then flooded with 1 mol/L hydrochloric acid, which precipitates the intact DNA and makes the medium opaque. Around DNase-positive colonies the DNA has been broken down, and a clear zone remains. With toluidine blue, positive colonies show a pink zone.
Typical reactions
| Organism | Reaction |
| S. aureus | DNase positive – clear zone around the colony |
| E. coli | DNase negative – no zone |
Technical data
| Preparation | 42.0 g/L; boil to dissolve, autoclave 121 °C 15 min |
| Final pH | 7.3 ± 0.2 |
| Incubation | 36 ± 1 °C, 24 ± 2 h |
| Storage | Dry place, away from light |
| Shelf life | 3 years unopened |
Applications and practical notes
Selective and differential agars for Staphylococcus aureus and other coagulase-positive staphylococci are used in food, feed, cosmetics and pharmaceutical testing, for example according to ISO 6888-1 and FDA BAM Chapter 12. Typical applications include:
- Enumeration of coagulase-positive staphylococci in food and feed
- Testing of dairy products, meat, ready meals and confectionery
- Microbial limit tests of non-sterile pharmaceutical and cosmetic products
- Hygiene monitoring of food handlers and surfaces
Working with DNase Agar: Inoculate a known positive and a negative strain on every plate and read the zones within a few minutes after adding the acid.
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.
DNase 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 DNase Agar, please send us a request. With every delivery of DNase Agar you receive the lot number and expiry date, and on request we send the available documentation for DNase Agar.
Where DNase 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 |
|---|---|---|
| DNase Agar | PRO7549 | 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.
