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Principle
- Motility urea indole agar base is composed of L-tryptophan, dextrose, sodium chloride, phenol red, and agar. L-tryptophan provides essential amino acids.
- Dextrose is a carbon and energy source. Sodium chloride maintains osmatic balance. The medium is fortified with urea, which is a substrate for the urease enzyme and phenol red is 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. The entire test must be performed in different test tubes.
- If the single tube is inoculated, the results for urease production should be noted prior to the indole reaction, as the addition of Kovacs reagent, decolorizes the medium, due to a drop in pH. The motility is detected by the growth away from stable.
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