Salmonella detection · Step 3 – selective isolation
XLD Agar, granulated – selective plating medium for Salmonella and Shigella
Granulated Xylose Lysine Deoxycholate (XLD) Agar for the isolation of Salmonella and Shigella from food, feed and environmental samples. Granulated media are low in dust and dissolve quickly, which makes routine preparation of larger volumes cleaner and faster.
- Typical Salmonella colonies: red with black centres
- Granulated, low-dust form
- Granules, 250 g bottle · COLO code PRO7638
How XLD Agar works
Sodium deoxycholate inhibits Gram-positive bacteria. Most enteric bacteria ferment xylose and turn the phenol red indicator yellow; Salmonella also decarboxylates lysine, which shifts the pH back to alkaline, so its colonies stay red. Sodium thiosulfate and ferric ammonium citrate show hydrogen sulfide production as black colony centres. Shigella forms red colonies without black centres.
Typical colony appearance
| Organism | Colonies on XLD Agar |
| Salmonella | red, with black centres |
| Shigella | red, without black centres |
Technical data
| Preparation | 56.9 g per litre of water; heat to boiling with stirring until dissolved, do not autoclave; cool to 48 ± 2 °C and pour plates |
| Final pH | 7.4 ± 0.2 |
| Incubation | 35–37 °C, 24 h |
| Storage | Dry, dark place; close the cap tightly after use |
| Shelf life | 3 years unopened |
Applications and practical notes
Granulated XLD Agar is one of the plating media for Salmonella in ISO 6579-1 and is also used in the FDA BAM Chapter 5 procedures. Typical applications include:
- meat, poultry, eggs and egg products
- milk, dairy products and infant formula
- feed, spices and dry foods
- environmental swabs from the food production area
Working with XLD Agar: Streak a loopful of each enrichment culture onto XLD Agar and onto a second selective agar of a different principle. Plates are incubated inverted and read after 24 h; colonies typical for Salmonella are confirmed biochemically and serologically.
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.
XLD 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 XLD Agar, please send us a request.
Where XLD Agar fits in the Salmonella workflow
- Pre-enrichment – Buffered Peptone Water or Lactose Broth
- Selective enrichment – RVS Broth and MKTTn Broth
- Selective isolation – XLD Agar plus a second selective or chromogenic agar
- Confirmation – TSI, Lysine Iron Agar, Urea Agar, latex and biochemical identification
See the complete Salmonella set in the Microbiology Catalogue →
Ordering information
| Product | COLO code | Pack |
|---|---|---|
| XLD Agar, granulated | PRO7638 | 250 g |
| XLD Agar (Pharmacopoeia), granulated | PRO7637 | 250 g |
| XLD Agar, dehydrated | PRO7437 | 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.
