Salmonella detection · Step 3 – selective isolation
XLT-4 Agar Base – selective agar for Salmonella in heavily contaminated samples
XLT-4 Agar is a highly selective plating medium for the isolation of non-typhoid Salmonella from samples with a heavy accompanying flora, such as poultry, meat and environmental samples. The base is completed with XLT-4 Agar Supplement before use.
- Salmonella: black or black-centred colonies
- Strong suppression of Proteus, Pseudomonas and Providencia
- Dehydrated powder, 500 g bottle · COLO code PRO7574
How XLT-4 Agar works
The XLT-4 supplement (tergitol 4) inhibits Proteus, Pseudomonas and other competing flora that often overgrow other agars. Sugar fermenters turn phenol red yellow, while Salmonella decarboxylates lysine and produces hydrogen sulfide, giving black or black-centred colonies.
Typical colony appearance
| Organism | Colonies |
| Salmonella | black or colourless with black centres |
| Sugar fermenters | yellow |
Technical data
| Preparation | 59 g per litre of water; heat to boiling until dissolved, do not autoclave; cool to 45 °C and add 1 vial of XLT-4 supplement per 200 mL |
| Final pH | 7.4 ± 0.2 |
| Incubation | 35–37 °C, 18–48 h |
| Storage | Dry, dark place; close the cap tightly after use |
| Shelf life | 3 years unopened |
Applications and practical notes
XLT-4 Agar is used for the isolation of non-typhoid Salmonella from heavily contaminated samples, as described in FDA BAM Chapter 5. Typical applications include:
- raw poultry and meat
- environmental samples from poultry and pig farms
- feed and animal by-products
- faecal and boot swab samples
Working with XLT-4 Agar Base: Add the XLT-4 supplement only to the cooled base. Plates can be read after 24 h and, if needed, again after 48 h, because some strains develop black centres later.
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.
XLT-4 Agar Base is supplied by COLO.Science in the pack sizes listed under Ordering information. For larger quantities, regular deliveries or method-specific sets that include XLT-4 Agar Base, please send us a request. With every delivery of XLT-4 Agar Base you receive the lot number and expiry date, and on request we send the available documentation for XLT-4 Agar Base. If you are changing to XLT-4 Agar Base from another supplier, we are happy to advise on the transition.
Where XLT-4 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 |
|---|---|---|
| XLT-4 Agar Base, dehydrated | PRO7574 | 500 g |
| XLT-4 Agar Supplement | PRO7706 | 5 vials |
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.
