Listeria detection · Step 1 – primary enrichment
Half-Fraser Broth – primary enrichment for Listeria
Half-Fraser Broth is the primary selective enrichment broth for Listeria monocytogenes and other Listeria species in food and environmental samples. It contains half the concentration of selective agents of Fraser Broth, which helps injured cells to recover. The base is completed with the Half-Fraser supplement before use.
- Primary enrichment step of the Listeria method
- Aesculin hydrolysis shows Listeria growth by blackening
- Dehydrated powder, 500 g bottle · COLO code PRO7536
How Half-Fraser Broth works
Lithium chloride, nalidixic acid and acriflavine suppress accompanying bacteria, at a lower concentration than in Fraser Broth so that stressed Listeria can recover. Listeria hydrolyses aesculin, and the product reacts with ferric ammonium citrate, so the broth turns 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 Half-Fraser supplement (one set per 225 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
Half-Fraser Broth is the primary 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 Half-Fraser Broth: Dissolve the powder in water at room temperature before heating, which avoids turbidity and precipitate. The usual ratio is 25 g of sample in 225 mL of complete Half-Fraser Broth.
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.
Half-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 Half-Fraser Broth, please send us a request. With every delivery of Half-Fraser Broth you receive the lot number and expiry date, and on request we send the available documentation for Half-Fraser Broth.
Where Half-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 |
|---|---|---|
| Half-Fraser Broth Base, dehydrated | PRO7536 | 500 g |
| Half-Fraser Selective Supplement | PRO7747 | 2 × 5 vials |
| Fraser Broth Base, dehydrated | PRO7446 | 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.
