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Indole test positive: appearance of pink layer at top (e.g. Escherichia coli) 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. Pure bacterial culture must be grown in sterile tryptophan or peptone broth for 24–48 hours before performing the test.
It is used for the diagnostical indole test, to determine the ability of the organism to split indole from the amino acid tryptophan. The indole produced yields a red complex with para-dimethylaminobenzaldehyde under the given conditions. [1] This was invented by the Hungarian physician Nicholas Kovács and was published in 1928.
To test the broth for indole production, Kovac's reagent. Kovac's reagent consist of amyl alcohol and para-dimethylaminobenzaldehyde and concentrated hydrochloric acid . Kovac's reagent is actually used to determine ability of an organism to separate indole from amino acid tryptophan and it is added after incubation.
para-Dimethylaminobenzaldehyde is an organic compound containing amine and aldehyde moieties which is used in Ehrlich's reagent and Kovac's reagent to test for indoles. The carbonyl group typically reacts with the electron rich 2-position of the indole but may also react at the C-3 or N-1 positions. [2] It may also be used for determination of ...
The Leimgruber–Batcho indole synthesis is an efficient method of synthesizing indole and substituted indoles. [29] Originally disclosed in a patent in 1976, this method is high-yielding and can generate substituted indoles.
The Ehrlich reagent is similar to a number of other indole tests: The van Urk reagent, which uses 0.125 g of p-DMAB, 0.2 mL of ferric chloride solution (25 mg/mL) in 100 mL of 65% sulfuric acid. [9] [10] [11] This is sometimes referred to as the Hofmann reagent or p-DMAB-TS (Test Solution) and gives slightly different colours with different ...
An indole test will differentiate Enterobacter from Escherichia, as Enterobacter are indole negative and Escherichia is positive. [5] Enterobacter are distinguished from Klebsiella because of their differences in motility. [5] Klebsiella are non-motile, Gram-negative bacilli ranging from 1–2 μm in length. [6]
Sulphide Indole Motility (SIM) medium is a bacterial growth medium which tests for the ability to reduce sulfates, the ability to produce indoles, and motility. [1] This combination of challenges in one mixture is convenient and commercially available in stab tubes.