Principle
- Urea indole medium is composed of L-tryptophan, sodium chloride, monobasic potassium phosphate, dibasic potassium phosphate, urea, and phenol red. L-tryptophan provides essential amino acids.
- Sodium chloride maintains osmatic balance. The monobasic and dibasic phosphates are buffering agents. Urea is a substrate for the urease enzyme and phenol red is the pH indicator dye. the urea hydrolyzing bacteria produce urease enzyme leads to an increase in the pH of the medium, resulting medium turning pink.
- While non-urease-producing bacterial medium remains light orange colored. The indole-producing bacteria convert L-tryptophan to skatole and indole, which is detected with the help of the Kovacs reagent.
- The appearance of a pink to red color in the reagent is interpreted as a positive indole test. Both the test must be performed in two different test tubes. If the single tube is inoculated, the results for urease production should be noted before the indole reaction, as the addition of Kovacs reagent, decolorizes the medium, due to a drop in pH.
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