R2A Agar : Use, Composition and Principle
Reasoner and Geldreich of the U.S. Environmental Protection Agency developed R2A Agar for the recovery and isolation of aerobic and facultative anaerobic heterotrophic bacteria from treated potable water.
R2A agar (Reasoner's 2A agar) is a culture medium developed to study bacteria which normally inhabit potable water. These bacteria tend to be slow-growing species and would quickly be suppressed by faster-growing species on a richer culture medium.
Principle:
* Casein acid hydrolysate, proteose peptone and yeast extract provide nitrogen, vitamins, amino acids, carbon and minerals.
* Dextrose serves as an energy source.
* Soluble starch aids in the recovery of injured organisms by absorbing toxic metabolic byproducts while sodium pyruvate increases the recovery of stressed cells.
* Magnesium sulphate is a source of divalent cations and sulphate.
* Dipotassium phosphate is used to balance the pH of the medium.
* The number of colonies on a plate are reported as CFU (Colony Forming Units) per volume of sample.
Composition:
Ingredients
|
Gms/Litre
|
Casein acid hydrolysate
|
0.500
|
Yeast extract
|
0.500
|
Proteose peptone
|
0.500
|
Dextrose
|
0.500
|
Starch, soluble
|
0.500
|
Dipotassium phosphate
|
0.300
|
Magnesium sulphate
|
0.024
|
Sodium pyruvate
|
0.300
|
Agar
|
15.0
|
Final
pH 7.2 +/- 0.2 at 25°C.
|
|
*
Adjusted and/or supplemented as required to meet performance criteria.
Reference:
1.
https://mltgeeks.com
2.
Himedia
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