Coliforms and E. coli · β-glucuronidase-positive E. coli count
TBX Agar – the reference medium for E. coli counts
TBX Agar (Tryptone Bile X-glucuronide Agar) is the medium for the enumeration of β-glucuronidase-positive E. coli in food and feed according to ISO 16649. E. coli forms blue-green colonies.
- Medium of ISO 16649 for E. coli counts
- Blue-green colonies, no further confirmation
- Incubation at 44 °C
How TBX Agar works
Bile salts inhibit Gram-positive bacteria. β-glucuronidase of E. coli splits the chromogen X-glucuronide, and the blue-green product stays in the colony. Incubation at 44 °C increases selectivity.
Typical colony appearance
| Organism | Colonies |
| E. coli | Blue-green colonies |
| Citrobacter freundii | White colonies |
Technical data
| Preparation | 34.6 g/L; boil to dissolve; autoclave 121°C 15 min; cool to 50°C |
| Final pH | 7.2±0.2 |
| Incubation | 35-37°C for 24 h (QC conditions) |
| Storage | 2-30°C, tightly capped, dry, protected from light |
Applications and practical notes
Plate count and isolation media for coliforms and E. coli are used in food, feed, water and hygiene testing, for example according to ISO 4832 and ISO 16649-2. Typical applications include:
- Coliform and E. coli colony counts in food and feed
- Isolation of lactose-fermenting Gram-negative bacteria
- Process hygiene criteria in dairy, meat and vegetable production
- Teaching and routine quality-control laboratories
Working with TBX Agar: For stressed cells, follow the resuscitation step of your method before incubation at 44 °C.
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.
TBX 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 TBX Agar, please send us a request. With every delivery of TBX Agar you receive the lot number and expiry date, and on request we send the available documentation for TBX Agar.
Where TBX Agar fits in coliform and E. coli testing
- Presumptive test – Lauryl Sulfate Tryptose Broth (MPN) or VRBL / chromogenic agar (colony count)
- Confirmation – BGLB Broth for coliforms; EC or EC-MUG Broth at 44.5 °C for E. coli
- Isolation – EMB, MacConkey, TBX or chromogenic E. coli agar
- Identification – IMViC kit; for O157 and STEC: SMAC or chromogenic O157 agar, latex and PCR
Ordering information
| Product | COLO code | Pack |
|---|---|---|
| TBX Agar (Tryptone Bile X-glucuronide) | PRO7593 | 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.
