Chromogenic media
TBX Chromogenic Agar (Tryptone Bile X-Glucuronide) ISO
Selective medium for the detection and enumeration of Escherichia coli in foods.
- Cat. No.
- LC-1151
- Category
- Chromogenic media
- Format
- 500 g
- Storage
- 2 to 25 °C
- Minimum guaranteed shelf life
- 12 months
- Standards
- ISO 11133ISO 16649
- Also available
- Ready-to-use medium, 3 formats (LC-982)
TBX Chromogenic Agar (Tryptone Bile X-Glucuronide) is based on Tryptone Bile Salts Agar medium, used to detect and enumerate E. coli in foods, with the addition of a chromogenic agent, X-beta-D-glucuronide, to detect the presence of the enzyme glucuronidase, which is highly specific for E. coli.
Key features
Applications
Detection and selective enumeration of Escherichia coli.
Industry
Food.
Standards
ISO 11133, ISO 16649.
Preparation
36.6 g in one liter of distilled water; boil for one minute, sterilize in autoclave at 121 °C for 15 minutes.
Principles and uses
The released chromophore in TBX Agar is colored and target colonies are easily identified. E. coli absorbs the chromogenic agent X-beta-D-glucuronide, and the intracellular glucuronidase enzyme activity breaks the bond between the chromophore and the glucuronide. The released chromophore is colored and builds up within the cells, causing the E. coli colonies to be blue-green colored.
Casein peptone provides nitrogen, vitamins, minerals and amino acids essential for growth. Bile salts are inhibitors to other Gram-positive organisms and suppress coliform bacteria. Bacteriological agar is the solidifying agent.
ISO 16649 specifies a horizontal method for the enumeration of beta-glucuronidase-positive E. coli in products intended for human consumption or for the feeding of animals.
The beta-glucuronidase-negative E. coli colonies are colorless, e.g. E. coli O157:H7. The high temperatures (44 °C) inhibit the growth of E. coli O157:H7.
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) | 7.2 ± 0.2 |
| Amount per litre | 36.6 g |
| Storage | 2 to 25 °C |
Formula
| Ingredient | g/L |
|---|---|
| Enzymatic digest of casein | 20 |
| Bacteriological agar | 15 |
| Bile salts No. 3 | 1.5 |
| 5-bromo-4-chloro-3-indolyl-beta-D-glucuronic acid | 0.075 |
Preparation and use
Preparation
Suspend 36.6 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 15 minutes. Cool to 45-50 °C, mix well and dispense into plates.
According to ISO 16649
Enumeration of beta-glucuronidase-positive Escherichia coli according to ISO 16649:
- Inoculate the TBX agar either by the plating method in depth, seeding on the surface or by the membrane filtration method.
- The membrane filtration method and the enumeration by the most probable number technique need a previous resuscitation stage in Minerals Modified Glutamate Agar or Broth, MMGA or MMGB (LC-1365).
- Incubate the plates of TBX agar for 21 hours at a temperature of 44 °C.
- Calculate the number of beta-glucuronidase-positive Escherichia coli colonies from the number of typical blue colonies.
Quality control
According to ISO 11133
Incubation conditions: 44 ± 1 °C / 21 ± 3 h.
Inoculation conditions: productivity quantitative (100 CFU, min. 50 CFU) / productivity qualitative (10³-10⁴ CFU) / selectivity (10⁴-10⁶ CFU) / specificity (10³-10⁴ CFU).
Reference media: TBX.
| Microorganism | Specification | Characteristic reaction |
|---|---|---|
| Enterococcus faecalisATCC 19433 | Total inhibition (0) | |
| Escherichia coliATCC 25922 | Good growth (2) > 50% | Blue colonies |
| Pseudomonas aeruginosaATCC 27853 | White to green-beige colonies | |
| Enterococcus faecalisATCC 29212 | Total inhibition (0) | |
| Citrobacter freundiiATCC 43864 | White to green-beige colonies | |
| Escherichia coliATCC 8739 | Good growth (2) > 50% | Blue colonies |
| Escherichia coliCECT 9153 | Good growth (2) > 50% | Blue colonies |
Bibliography
- International standard ISO 16649: Microbiology of food and animal feeding stuffs. Horizontal method for the enumeration of presumptive beta-glucuronidase-positive.
What you receive
The product
Shipped under controlled temperature when the product requires it.
Lot certificate
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Frequently asked questions
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