Dehydrated culture media
MRS Agar
For the growth of lactobacilli.
- Cat. No.
- LC-1043
- Category
- Dehydrated culture media
- Format
- 500 g
- Storage
- 2 to 8 °C
- Minimum guaranteed shelf life
- 15 months
- Also available
- Ready-to-use medium, 3 formats (LC-943)
MRS Agar is a selective medium, based on the formulation developed by de Man, Rogosa and Sharpe to provide a medium that would support the good growth of lactobacilli in general, but in particular of those strains which showed poor growth in existing media such as L. brevis and L. fermenti, replacing a variable product (tomato juice).
Key features
Applications
Selective enrichment of lactobacilli.
Industry
Alcoholic beverages, dairy products, food.
Preparation
62 g in one liter of distilled water; boil for one minute, sterilize in autoclave at 121 °C for 12 minutes.
Principles and uses
The medium is apt for the growth of lactic acid bacteria, including Lactobacillus, Pediococcus and Leuconostoc.
Ammonium citrate, at a low pH, inhibits most microorganisms, but allows the growth of Lactobacilli. Dipotassium phosphate and Sodium acetate are buffer agents to maintain a low pH. Tween 80 is an emulsifier. Manganese and Magnesium sulfates are sources of ions and sulfate. Bacteriological peptone and Beef extract provide nitrogen, vitamins, minerals and amino acids essential for growth. Yeast extract is a source of vitamins, particularly the B-group. Dextrose is the fermentable carbohydrate. Bacteriological agar is the solidifying agent.
Lactobacilli are microaerophilic and generally require layered plates for aerobic cultivation on solid media. Submerged or surface colonies may be compact or feathery, and are small, opaque and white.
Technical specifications
| Solubility | Without residues |
|---|---|
| Appearance | Fine powder |
| Color of the dehydrated medium | Beige |
| Color of the prepared medium | Amber, slightly opalescent |
| Final pH (25 °C) | 6.2 ± 0.2 |
| Amount per litre | 62 g |
| Storage | 2 to 8 °C |
Formula
| Ingredient | g/L |
|---|---|
| Bacteriological agar | 10 |
| Bacteriological peptone | 10 |
| Dextrose | 20 |
| Dipotassium phosphate | 2 |
| Magnesium sulfate | 0.2 |
| Manganese sulfate | 0.05 |
| Beef extract | 8 |
| Sodium acetate | 5 |
| Tween 80 | 1 |
| Yeast extract | 4 |
| Ammonium citrate | 2 |
Preparation and use
Preparation
Suspend 62 grams of the medium in one liter of distilled water. Mix well and dissolve by heating with frequent agitation. Boil for one minute until complete dissolution. Sterilize in autoclave at 121 °C for 12 minutes. Cool to 45-50 °C, mix well and dispense into plates.
Instructions for use
For the enumeration of mesophilic lactic acid bacteria:
- Pour 1 mL of the previously diluted sample into a sterile Petri dish.
- Add a first layer of the cooled medium (45-50 °C).
- After solidification, a second layer is poured.
- Incubate the plates up to 3 days at 35 °C or up to 5 days at 30 °C. If possible, incubate the plates in a CO₂ atmosphere.
- It is important to maintain a humid atmosphere because the plates should not dry out during incubation.
- The growth of some Lactobacillus strains is inhibited at a higher pH of 6.0 and it is necessary to acidify the medium to promote growth. To acidify the medium some drops of acetic acid can be added.
Quality control
Microbiological test
Incubation conditions: 30 ± 1 °C / 72 ± 3 h.
Inoculation conditions: productivity quantitative (100 ± 20 CFU, min. 50 CFU) / selectivity (10⁴-10⁶ CFU).
Reference media: media batch MRS already validated.
| Microorganism | Specification |
|---|---|
| Lactobacillus sakeiATCC 15521 | Good growth, > 70% |
| Lactococcus lactis ssp. lactisATCC 19435 | Good growth, > 70% |
| Escherichia coliATCC 25922 | Moderate growth |
Bibliography
- Briggs M (1953) "An Improved Medium for Lactobacilli" J. Dairy Res. 20. 36-40.
- De Man, J.C. Rogosa, M., Sharpe, Elisabeth (1960) "A Medium for the Cultivation of Lactobacilli". J. Appl. Bact. 23. 130-135
What you receive
The product
Shipped under controlled temperature when the product requires it.
Lot certificate
Every lot comes with its certificate.
Tracked shipment
Follow your shipment live, from our warehouse to your lab.
Related products
Frequently asked questions
Can I ask for formats other than those listed?
Yes: custom formats and OEM packs are available on request. Tell us the quantities you need.
How do I see the prices?
Prices are shown after you sign in to the customer area, with your account discount already applied.
How long does delivery take?
We give you the availability with the quote, within 24 hours of your request.