I would like to ask about indole production medium composition... I add casein enzymatic hydrolysate or tryptone as tryptophan source... I found both sources were added, for sure one of them separately., but the results were different. Positive result when using casein and negative results using tryptone. So which one of them is true?
Principle of Indole Test. Tryptophan is an amino acid that can undergo deamination and hydrolysis by bacteria that express tryptophanase enzyme. ... In the spot test, indole combines, in the filter paper matrix, at an acid pH with p-Dimethylaminocinnamaldehyde (DMACA) to produce a blue to blue-green compound.
https://microbiologyinfo.com/indole-test-principle-reagents-procedure-result-interpretation-and-limitations/
The indole test is a qualitative procedure for determining the ability of bacteria to produce indole by deamination of tryptophan. Using Kovacs tube method, indole combines, in the presence of a tryptophan rich medium, with p-Dimethylaminobenzaldehyde at an acid pH in alcohol to produce a red-violet compound.
https://catalog.hardydiagnostics.com/cp_prod/Content/hugo/IndoleTestRgnts.htm
Casein peptone, another component of SIM Medium, is rich in tryptophan. Organisms possessing the enzyme tryptophanase degrade tryptophan to indole. Indole is detected upon the addition of Kovacs Reagent (Cat. ... Motile organisms extend from the stab line and produce turbidity or cloudiness throughout the medium.
https://catalog.hardydiagnostics.com/cp_prod/Content/hugo/SIMMedium.htm
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