Kovac’s Indole Reagent uniLAB, 100ml

Description

Reagent for detecting microbial indole in the identification of indole-positive and indole-negative microorganisms.

Mode of Action
Some microorganisms can cleave tryptophan which is especially abundant in trypticalle digested peptone to give pyruvic acid, ammonia and indole. Indole then reacts with 4-dimethylaminobenzaldehyde to form a dark red dye. As tryptophan also gives a colour reaction with 4-dimethylaminobenzaldehyde, it must be separated from the indole. This is achieved by selectively extracting indole with butanol.

Typical Composition
n-Butanol; hydrochloric acid; 4-dimethylaminobenzaldehyde.

Experimental Procedure and Evaluation
The strain purity of the organism to be tested must first be established; it is then inoculated into an appropriate culture medium (e.g. Standard II Nutrient Broth, Nitrate Broth, DEV Tryptophan Broth, SIM Medium, etc.) and incubated for 18-24hours at the optimal incubation temperature.

The medium is then covered with a layer of KOVÁCS’ indole reagent of about 0.5cm.
If indole is present the reagent layer turns cherry red in colour after a few minutes.

The reagent solution must be stored in the dark in the refrigerator, otherwise it may turn brown and cannot be used.