Coliforms and E. coli · Isolation and differentiation
Eosin Methylene Blue Agar – the green metallic sheen of E. coli
Eosin Methylene Blue Agar (EMB) is used to isolate and differentiate coliforms. E. coli forms dark colonies with a typical green metallic sheen, which makes it the classic medium for the completed coliform test.
- E. coli: black centre with green sheen
- Eosin and methylene blue inhibit Gram-positives
- Completed test after EC or BGLB Broth
How Eosin Methylene Blue Agar works
Eosin Y and methylene blue inhibit Gram-positive bacteria and form a complex at low pH. Strong lactose fermenters such as E. coli produce so much acid that the dye precipitates on the colony, giving the metallic sheen.
Typical colony appearance
| Organism | Colonies |
| E. coli | Dark centre, green metallic sheen |
| Other coliforms | Purple to pink, mucoid |
| Non-fermenters | Colourless to amber |
Technical data
| Preparation | 37.5 g/L; boil to dissolve, autoclave 121 °C 15 min, cool ~50 °C, pour plates |
| Final pH | 7.1 ± 0.2 |
| Incubation | 35-37 °C, 24 h |
| Storage | Dry, dark place; keep the container tightly closed |
| Shelf life | 3 years unopened |
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 Eosin Methylene Blue Agar: Streak from gas-positive EC tubes and pick typical colonies for IMViC tests.
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 coliform and E. coli methods: coliforms and E. coli are counted either by the multiple-tube (MPN) method, with a presumptive broth followed by confirmation broths, or by colony counts on selective agars. FDA BAM Chapter 4 describes both approaches for food and water, and ISO 16649-2 gives the colony-count method for β-glucuronidase-positive E. coli on TBX Agar. E. coli O157 and other STEC need dedicated media, serology and PCR. COLO.Science offers media, supplements, rapid tests, identification kits and QC strains for every step.
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.
Eosin Methylene Blue 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 Eosin Methylene Blue Agar, please send us a request. With every delivery of Eosin Methylene Blue Agar you receive the lot number and expiry date, and on request we send the available documentation for Eosin Methylene Blue Agar.
Where Eosin Methylene Blue 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 |
|---|---|---|
| Eosin Methylene Blue Agar (EMB) | PRO7457 | 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.
