Dehydrated culture media
ESTY Medium
Selective medium for the enumeration of Streptococcus thermophilus in yogurt.
- Cat. No.
- LC-1555
- Category
- Dehydrated culture media
- Format
- 500 g
- Storage
- 2 to 25 °C
- Minimum guaranteed shelf life
- 15 months
ESTY Medium is a medium recommended for the growth of lactic streptococci and their bacteriophages from yogurt and other dairy products.
Key features
Applications
Selective enumeration and selective isolation of Streptococcus.
Industry
Dairy products.
Preparation
48.25 g in 950 mL of distilled water; boil for one minute, sterilize in autoclave at 121 °C for 15 minutes, add 5 g of lactose.
Principles and uses
This medium is recommended for Streptococcus thermophilus isolation and enumeration in yogurt. Lactic streptococci produce acid and are difficult to grow. They are nutritionally fastidious and demand complex culture media for optimum growth. The glycerophosphate present in high concentrations acts as a pH regulator and inhibits Lactobacillus bulgaricus development, while the ascorbic acid promotes the growth of lactic streptococci. It is recommended for the maintenance of the starter cultures, where these microorganisms produce acids in their metabolism.
Beef extract, tryptone and soy peptone provide nitrogen, vitamins, minerals and amino acids essential for growth. Yeast extract is a source of vitamins, particularly of the B-group. Disodium glycerophosphate is a buffering agent. Ascorbic acid promotes the growth of lactic streptococci. Magnesium sulphate provides ions required in a large variety of enzymatic reactions, including DNA replication, and also acts as a buffer. Bacteriological agar is the solidifying agent.
Technical specifications
| Solubility | Without residues |
|---|---|
| Appearance | Fine powder |
| Color of the dehydrated medium | Beige |
| Color of the prepared medium | Amber |
| Final pH (25 °C) | 6.9 ± 0.2 |
| Amount | 48.25 g in 950 mL |
| Storage | 2 to 25 °C |
Formula
| Ingredient | g/L |
|---|---|
| Ascorbic acid | 0.5 |
| Bacteriological agar | 11 |
| Beef extract | 5 |
| Disodium glycerophosphate | 19 |
| Magnesium sulfate | 0.25 |
| Soy peptone | 5 |
| Tryptone | 5 |
| Yeast extract | 2.5 |
Preparation and use
Preparation
Suspend 48.25 grams of the medium in 950 mL 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 15 minutes. Cool to 45-50 °C and aseptically add 5 grams of lactose, previously reconstituted in 50 mL of distilled water. Sterilize the lactose solution by membrane filtration. Homogenize gently and dispense into Petri dishes.
Instructions for use
Streak plate method:
- In a Petri dish, add 12-15 mL of molten agar and let it solidify.
- Inoculate 10 µL of the initial suspension and/or diluted sample.
- Extend the inoculum with a sterile loop on the agar surface.
- Incubate the plates in an inverted position at a temperature of 35 ± 2 °C for 24-48 hours.
Quality control
Microbiological test
Incubation conditions: 35 ± 2 °C / 24-48 h.
| Microorganism | Specification |
|---|---|
| Lactobacillus bulgaricusATCC 11842 | Inhibited growth |
| Streptococcus thermophilusATCC 14486 | Good growth |
Bibliography
- Terzaghi, B.E. and W.E. Sandine. 1975. Improved medium for lactic streptococci and their bacteriophages. Appl. Microbiol. 29:807-813.
- International Dairy Federation 1981. Identification and enumeration of micro-organisms in fermented milks. Joint IDF/ISO/AOAC.
What you receive
The product
Shipped under controlled temperature when the product requires it.
Lot certificate
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Tracked shipment
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Frequently asked questions
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