Cosmetics testing · Neutralising agar
Modified Letheen Agar – plate count of cosmetics
Modified Letheen Agar is a neutralising agar for the total aerobic plate count of cosmetics and other products with preservatives. It is used together with Modified Letheen Broth.
- Neutralising agar for plate counts
- For cosmetics and preserved products
- Used with Modified Letheen Broth
How Modified Letheen Agar works
Lecithin and polysorbate 80 in the agar neutralise residual preservatives carried over with the sample, so that injured or inhibited bacteria can still form colonies.
Typical colony appearance
| Organism | Colonies |
| Staphylococcus aureus | Yellowish colonies |
| Escherichia coli, Pseudomonas aeruginosa | White colonies |
Technical data
| Preparation | 59.1 g/L; boil to dissolve, autoclave 121 °C 15 min, cool to about 50 °C and pour |
| Final pH | 7.2 ± 0.2 |
| Incubation | 28–32 °C, 48 h |
| Storage | Dry, dark place; keep the container tightly closed |
| Shelf life | 3 years unopened |
Applications and practical notes
Cosmetic products contain preservatives that must be neutralised before counting and detecting micro-organisms. Neutralising media with lecithin and polysorbate 80 are used in the ISO methods for cosmetics, such as ISO 21149. Typical applications include:
- Cosmetics and toiletries
- Products with preservatives
- Disinfectant residues on surfaces
- Personal care and household products
Working with Modified Letheen Agar: Incubate the plates at 28–32 °C for 48 hours before counting.
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 pharmacopoeial microbiological testing: the European Pharmacopoeia and the USP describe harmonised methods for non-sterile products – microbial enumeration (Ph. Eur. 2.6.12, USP <61>) and tests for specified micro-organisms (Ph. Eur. 2.6.13, USP <62>) – and the sterility test for sterile products (Ph. Eur. 2.6.1, USP <71>). The chapters define the media, incubation conditions and the growth promotion test that each batch of medium must pass with reference strains. COLO.Science offers the media, diluents, neutralisers and QC strains for these tests from one source.
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.
Modified Letheen 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 Modified Letheen Agar, please send us a request. With every delivery of Modified Letheen Agar you receive the lot number and expiry date, and on request we send the available documentation for Modified Letheen Agar.
Where Modified Letheen Agar fits in cosmetics testing
- Sample preparation – Buffered Sodium Chloride-Peptone Solution, Tryptic Soy Broth and neutralising diluents
- Microbial enumeration – Tryptic Soy Agar (TAMC) and Sabouraud Dextrose Agar (TYMC)
- Specified micro-organisms – enrichment in Tryptic Soy Broth, then MacConkey, Mannitol Salt, Cetrimide, XLD, VRBG, RCM and Columbia media
- Sterility test – Fluid Thioglycollate Medium and Tryptic Soy Broth, 14 days
See all pharmacopoeial media in the Microbiology Catalogue →
Ordering information
| Product | COLO code | Pack |
|---|---|---|
| Modified Letheen Agar | PRO7508 | 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.
