VLD 421: Veterinary Clinical Biochemistry and Laboratory Diagnosis-II (0+1)

INDOLE TEST

Principle

• Indole is a derivative of the amino acid tryptophan. Some bacteria have the ability to break down tryptophan using the enzyme tryptophanase, which results in production of Indole.
• The presence of indole in the test medium can be detected by adding Kovacs' reagent,contain p-dimehtylaminobenzaldehyde.
• A yellow Kovac's reagent reacts with indole and produces a red color on the top of the broth culture.

Methodology

• Inoculate the test organism into a tube of tryptophane broth.
• Incubate at 37^ºC for 48 hours.
• Add 0.5 ml of Kovac’s reagent to the broth culture.

Result

• Positive   : Observe for the development of a pink to wine colored ring. 
• Negative :  No colour change

Indole test 

Quality Control

• Positive   : Escherichia coli
• Negative : Klebsiella pneumoniae