Coliforms and E. coli · Isolation with clear differentiation
MacConkey Agar No. 3 – sharper differentiation of enteric bacteria
MacConkey Agar No. 3 is a MacConkey formulation with a refined bile salt mixture. It gives clear differentiation between lactose fermenters and non-fermenters and better suppression of Gram-positive cocci.
- Refined bile salts
- Pink-red colonies with bile precipitate
- Good suppression of Gram-positive cocci
How MacConkey Agar No. 3 works
Lactose-fermenting bacteria acidify the medium; neutral red turns the colonies pink-red and bile precipitates around them. Crystal violet and bile salts inhibit staphylococci and enterococci.
Typical colony appearance
| Organism | Colonies |
| Lactose fermenters | Pink-red colonies with bile precipitate halo |
| Non-fermenters | Colourless colonies |
Technical data
| Preparation | 51.5 g/L; boil to dissolve, dispense, autoclave 121 °C 15 min |
| Final pH | 7.2 ± 0.2 |
| Incubation | 36 ± 1 °C, 20-24 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 MacConkey Agar No. 3: Streak for isolated colonies, because the pink colour of crowded colonies can spread to nearby non-fermenters.
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.
MacConkey Agar No. 3 is supplied by COLO.Science in the pack sizes listed under Ordering information. For larger quantities, regular deliveries or method-specific sets that include MacConkey Agar No. 3, please send us a request. With every delivery of MacConkey Agar No. 3 you receive the lot number and expiry date, and on request we send the available documentation for MacConkey Agar No. 3.
Where MacConkey Agar No. 3 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 |
|---|---|---|
| MacConkey Agar No. 3 | PRO7519 | 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
COLO LabExperts
Polje ob Sotli 4, SI-3255, Slovenia
Quotations and technical support for culture media and microbiology products across our international sales territory. B2B prices are net, excluding VAT.
COLO.SCIENCE | MICROBIOLOGY SUPPORT
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.
