Lactic streptococci · Enumeration
M17 Agar – Streptococcus thermophilus and lactococci
M17 Agar is the medium for the count of lactic streptococci such as Streptococcus thermophilus and lactococci in yoghurt, cheese, starter cultures and other dairy products.
- For S. thermophilus and lactococci
- Strong phosphate buffer
- Yoghurt and starter cultures
How M17 Agar works
The sodium glycerophosphate buffer keeps the pH stable while lactic streptococci produce acid, so they grow well. Lactobacilli such as L. helveticus are suppressed and do not interfere with the count.
Typical colony appearance
| Organism | Colonies |
| Streptococcus thermophilus | White colonies |
| Lactobacillus helveticus | Inhibited |
Technical data
| Preparation | 55.0 g/L; boil to dissolve, autoclave 121 °C 15 min |
| Final pH | 7.2 ± 0.2 |
| Incubation | 37 ± 1 °C, 48 ± 2 h |
| Storage | Dry, dark place; keep the container tightly closed |
Applications and practical notes
Lactic acid bacteria are starter cultures in dairy, meat and fermented products, probiotic organisms and spoilage organisms in beverages; they are counted for example according to ISO 15214. Typical applications include:
- Yoghurt, cheese and fermented milk
- Starter cultures and probiotics
- Fermented meat and vegetables
- Beer, wine and soft drinks
Working with M17 Agar: Incubate the plates aerobically at 37 °C for 48 hours for S. thermophilus, and use MRS media in parallel for lactobacilli.
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 lactic acid bacteria methods: mesophilic lactic acid bacteria in food are counted on MRS agar at 30 °C according to ISO 15214. In dairy products and starter cultures, lactobacilli are counted on MRS media, lactic streptococci such as Streptococcus thermophilus on M17 media, and bifidobacteria on MRS with lithium mupirocin under anaerobic conditions. In breweries, beer-spoiling lactic acid bacteria are detected on Raka-Ray Agar. COLO.Science offers media, supplements and count plates for these methods.
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.
M17 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 M17 Agar, please send us a request. With every delivery of M17 Agar you receive the lot number and expiry date, and on request we send the available documentation for M17 Agar.
Where M17 Agar fits in lactic acid bacteria testing
- Lactobacilli and mesophilic LAB – MRS Agar and MRS Broth
- Bifidobacteria – MRS base with the modified MRS supplement (lithium mupirocin and cysteine), anaerobic
- Lactic streptococci and lactococci – M17 Agar and M17 Broth
- Beer spoilage – Raka-Ray Agar with supplement; count plates for fast results
See all lactic acid bacteria products in the Microbiology Catalogue →
Ordering information
| Product | COLO code | Pack |
|---|---|---|
| M17 Agar | PRO7547 | 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.
