Listeria detection · Step 3 – selective isolation
Chromogenic Listeria Agar – Ottaviani-Agosti type agar for Listeria monocytogenes
Chromogenic Listeria Agar of the Ottaviani and Agosti type is the first plating medium for Listeria in the reference method. Listeria species form blue-green colonies, and pathogenic L. monocytogenes is recognised by an additional opaque halo. The base is completed with the Listeria Chromogenic Selective Supplement.
- L. monocytogenes: blue-green colonies with an opaque white halo
- First plating agar of the Listeria reference method
- Dehydrated powder, 500 g bottle · COLO code PRO7594
How Chromogenic Listeria Agar works
A chromogenic substrate for β-glucosidase colours all Listeria colonies blue-green. A phospholipid substrate is cleaved by the phospholipase typical for L. monocytogenes and pathogenic L. ivanovii, which forms an opaque halo around the colonies. Lithium chloride and antibiotics in the supplement suppress the accompanying flora.
Typical colony appearance
| Organism | Colonies |
| L. monocytogenes | blue-green, small, smooth, with an opaque white halo |
| Other Listeria species | blue-green, without halo |
Typical colonies are confirmed by the tests described in the method.
Technical data
| Preparation | 72.1 g per litre of water; dissolve by heating, sterilise at 121 °C for 15 min, cool to about 50 °C; add one vial of supplement (dissolved in 10 mL sterile water) per 190 mL of base |
| Final pH | 7.2 ± 0.2 |
| Incubation | 35–37 °C, 24 ± 3 h |
| Storage | Powder 2–30 °C, dry and dark |
| Shelf life | 2 years |
Applications and practical notes
Chromogenic Listeria Agar of the Ottaviani-Agosti type is the first plating medium in ISO 11290-1. Typical applications include:
- ready-to-eat foods, cooked meat products and delicatessen
- milk, cheese and other dairy products
- fish, seafood and smoked fish
- environmental swabs from food production areas
Working with Chromogenic Listeria Agar: Streak a loopful of the enrichment culture so that well-isolated colonies develop, and incubate the plates inverted. Typical colonies are subcultured on TSYEA for confirmation.
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.
Chromogenic Listeria 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 Chromogenic Listeria Agar, please send us a request. With every delivery of Chromogenic Listeria Agar you receive the lot number and expiry date, and on request we send the available documentation for Chromogenic Listeria Agar.
Where Chromogenic Listeria Agar fits in the Listeria workflow
- Primary enrichment – Half-Fraser Broth
- Secondary enrichment – Fraser Broth
- Selective isolation – chromogenic Listeria agar (Ottaviani-Agosti type) plus PALCAM or Oxford Agar
- Confirmation – subculture on TSYEA, biochemical identification and latex
Ordering information
| Product | COLO code | Pack |
|---|---|---|
| Chromogenic Listeria Agar (Ottaviani-Agosti type) | PRO7594 | 500 g |
| Listeria Chromogenic Selective Supplement | PRO7727 | 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.
