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Principle
- Urea agar base is composed of peptone, dextrose, sodium chloride, monobasic potassium phosphate, phenol red, and agar.
- Peptone provides the carbon and nitrogen required for the growth of organisms. Dextrose is the energy source. Sodium chloride maintains the osmotic equilibrium and phosphates act as buffering agents.
- Many urinary tract infections cause organisms to produce urease enzyme, which catalyzes the splitting of urea in the presence of water to release two molecules of ammonia and carbon dioxide.
- The ammonia combines with the carbon dioxide and water to form ammonium carbonate, which turns the medium alkaline, and changes the color of the medium from light orange at pH 6.8 to magenta pink at pH 8.1 due to the presence of phenol red.
- Rapid urease-positive organisms turn the entire medium pink within 24 hours.
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