Listeria detection · Step 2 – secondary enrichment
Fraser Broth – secondary enrichment for Listeria
Fraser Broth is the secondary selective enrichment broth for Listeria monocytogenes and other Listeria species. It is inoculated from the Half-Fraser primary enrichment and completed with the Fraser supplement before use.
- Secondary enrichment step of the Listeria method
- Blackening of the broth indicates aesculin-positive Listeria
- Dehydrated powder, 500 g bottle · COLO code PRO7446
How Fraser Broth works
Lithium chloride, nalidixic acid and acriflavine at full concentration suppress the accompanying flora, while Listeria continues to grow. Aesculin hydrolysis by Listeria, together with ferric ammonium citrate, turns the broth black.
Reading the broth
| Observation | Meaning |
| Blackening of the broth | aesculin hydrolysis – possible Listeria |
| No blackening | subculture anyway as required by the method |
Technical data
| Preparation | 57.4 g per litre of water; dissolve at room temperature, sterilise at 121 °C for 15 min, cool to about 50 °C and add the Fraser supplement (one set per 100 mL) |
| Final pH | 7.2 ± 0.2 |
| Storage | Dry, dark place; close the cap tightly after use |
| Shelf life | 3 years |
Applications and practical notes
Fraser Broth is the secondary enrichment broth 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 Fraser Broth: Transfer 0.1 mL of the incubated Half-Fraser culture into 10 mL of complete Fraser Broth. Dissolve the powder at room temperature before heating to avoid a precipitate.
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.
Fraser Broth is supplied by COLO.Science in the pack sizes listed under Ordering information. For larger quantities, regular deliveries or method-specific sets that include Fraser Broth, please send us a request. With every delivery of Fraser Broth you receive the lot number and expiry date, and on request we send the available documentation for Fraser Broth.
Where Fraser Broth 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 |
|---|---|---|
| Fraser Broth Base, dehydrated | PRO7446 | 500 g |
| Fraser Selective Supplement | PRO7736 | 2 × 5 vials |
| Fraser Broth (FB2) Supplement | PRO7677 | 10 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
COLO LabExperts
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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.
