Spot Indole Test- Objective, Principle, Procedure, Results, Limitations

The objective of the spot indole test is to determine the ability of an organism to produce indole using the tryptophanase enzyme.

The principle of the spot indole test is based on the ability of some bacteria to produce the enzyme tryptophanase, which catalyzes the hydrolysis of the amino acid tryptophan into indole, pyruvic acid, and ammonia.

1. Saturate a piece of filter paper with the 1% p-dimethylaminocinnamaldehyde (DMACA) reagent.
2. Use a wooden stick or a bacteriologic loop to remove a small portion of a bacterial colony from the agar surface.
3. Rub the bacterial sample on the filter paper gently and evenly.
4. Observe for color development within 1 to 3 minutes.

The result of the spot indole test depends on the color development on the filter paper within 1 to 3 minutes after rubbing the bacterial sample.

The spot indole test has some limitations that should be considered before performing and interpreting the test.

Quality control is an essential step to ensure the accuracy and reliability of the spot indole test.

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The spot indole test is a rapid and simple method to detect the production of indole by bacteria.

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