Merck, 1.09293, KOVACS′ indole reagent

General description
Kovac′s reagent is a biochemical reagent composed of n-Butanol, hydrochloric acid, and 4-dimethylaminobenzaldehyde. It is used for the detection of indole producing microorganisms. Tryptophan is abundant in trypticalle digested peptone. Some microorganisms can cleave tryptophan to give pyruvic acid, ammonia, and indole. Indole then reacts with 4-dimethylaminobenzaldehyde to form a dark red dye. As tryptophan also gives a color reaction with 4 dimethylaminobenzaldehyde, it must be separated from the indole. This is achieved by selectively extracting indole with butanol.
Application
Kovac′s Indole reagent is used for the detection of indole producing microorganisms in food and beverages, and environmental samples. This is suitable for the identification of E. coli.
Preparation Note
No metal containers. Keep the container tightly closed in a dry and well-ventilated place. Keep away from heat and sources of ignition
Analysis Note
Indole formation (Escherichia coli ATCC 25922 (WDCM 00013)): +
Indole formation (Proteus vulgaris ATCC 8427): +
Indole formation (Enterobacter aerogenes ATCC 13048): -
Tested in DEV-Tryptophan broth art. no. 1.10694. (after incubation 24 hrs.; 35 °C aerobic).
Other Notes
The reagent solution must be stored in the dark in the refrigerator, otherwise it may turn brown and cannot be used.