Coliforms and E. coli · Coliform plate count
Deoxycholate Agar – coliforms in milk and dairy products
Deoxycholate Agar is a selective medium for the count and isolation of coliforms, especially in milk and dairy products. Lactose fermenters form red colonies, non-fermenters remain colourless.
- Sodium deoxycholate inhibits Gram-positives
- Red colonies = lactose fermenters
- For pour-plate counts
How Deoxycholate Agar works
Sodium deoxycholate suppresses Gram-positive bacteria. Lactose fermentation lowers the pH and neutral red turns the colonies red. The medium is boiled and poured without autoclaving.
Typical colony appearance
| Organism | Colonies |
| Lactose fermenters | Red colonies |
| Non-fermenters | Colourless colonies |
Technical data
| Preparation | 45 g/L; boil to dissolve, cool to ~50 °C and pour plates (no autoclaving stated) |
| Final pH | 7.4 ± 0.2 |
| Incubation | 35-37 °C, 18-24 h |
| Storage | Dry, dark place; keep the container tightly closed |
| Shelf life | 3 years unopened |
Applications and practical notes
Plate count and isolation media for coliforms and E. coli are used in food, feed, water and hygiene testing, for example according to ISO 4832 and ISO 16649-2. Typical applications include:
- Coliform and E. coli colony counts in food and feed
- Isolation of lactose-fermenting Gram-negative bacteria
- Process hygiene criteria in dairy, meat and vegetable production
- Teaching and routine quality-control laboratories
Working with Deoxycholate Agar: Use freshly prepared medium and avoid overheating, which can reduce selectivity.
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 Salmonella culture method: the reference method for Salmonella in the food chain, ISO 6579-1, has four steps: non-selective pre-enrichment, selective enrichment in two broths, plating on two selective agars and confirmation of typical colonies. The FDA BAM Chapter 5 follows the same principle with media adapted to different food types. Rapid tests and identification kits shorten the time to result, but positive screening results are usually confirmed by the culture method. COLO.Science offers products for every step, so that one supplier covers the whole procedure.
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.
Deoxycholate 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 Deoxycholate Agar, please send us a request. With every delivery of Deoxycholate Agar you receive the lot number and expiry date, and on request we send the available documentation for Deoxycholate Agar.
Where Deoxycholate Agar fits in coliform and E. coli testing
- Presumptive test – Lauryl Sulfate Tryptose Broth (MPN) or VRBL / chromogenic agar (colony count)
- Confirmation – BGLB Broth for coliforms; EC or EC-MUG Broth at 44.5 °C for E. coli
- Isolation – EMB, MacConkey, TBX or chromogenic E. coli agar
- Identification – IMViC kit; for O157 and STEC: SMAC or chromogenic O157 agar, latex and PCR
Ordering information
| Product | COLO code | Pack |
|---|---|---|
| Deoxycholate Agar | PRO7509 | 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.
