![]() ![]() The isoamyl alcohol forms a complex with rosindole dye, which causes it to precipitate. The para-Dimethylaminobenzaldehyde reacts with indole present in the medium to form a red rosindole dye. The positive red color forms as a result of a series of reactions. This is due to the presence of skatole, also known as methyl indole or methylated indole, another possible product of tryptophan degradation. A variable result can also occur, showing an orange color as a result. Following incubation, five drops of Kovac's reagent ( isoamyl alcohol, para-Dimethylaminobenzaldehyde, concentrated hydrochloric acid) are added to the culture broth.Ī positive result is shown by the presence of a red or reddish-violet color in the surface alcohol layer of the broth. Pure bacterial culture must be grown in sterile tryptophan or peptone broth for 24–48 hours before performing the test. Like many biochemical tests on bacteria, results of an indole test are indicated by a change in color following a reaction with an added reagent. Performing a test Indole test positive: appearance of pink layer at top (e.g. Pyridoxal phosphate is required as a coenzyme. Final products of the reaction are indole, pyruvic acid, ammonium (NH 4 +) and energy. Tryptophanase catalyzes the deamination reaction, during which the amine (-NH 2) group of the tryptophan molecule is removed. Indole is generated by reductive deamination from tryptophan via the intermediate molecule indolepyruvic acid. This division is performed by a chain of a number of different intracellular enzymes, a system generally referred to as " tryptophanase." Biochemistry The indole test is a biochemical test performed on bacterial species to determine the ability of the organism to convert tryptophan into indole. JSTOR ( November 2022) ( Learn how and when to remove this template message).Unsourced material may be challenged and removed. ![]() Please help improve this article by adding citations to reliable sources. This article needs additional citations for verification. ![]()
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