Page 118 - MNUmicrobiology practical 2025

General Microbiology & Immunology (PM 401) second level Semester 4 2024/2025

12- IMViC
➢ Indole

➢ Methyl red

➢ Voges-Proskauer

➢ Citrate .

The IMViC tests are employed for the identification of Enterobacteriaeae (enterics
which includes such organisms as Klebsiella, Enterobacter, and Escherichia coli.

A- Indole test (Tryptophan Hydrolysis)
• Purpose: To detect production of tryptophanase.
• Media: Tryptone broth media
• Mechanism/reactions: Tryptophanase causes the hydrolysis of Tryptophan → indole
+ pyruvic acid
• Procedure:

• Incubate tryptone broth media with the tested organism.

• The presence of indole can be detected through the use of Kovac’s reagent (para

dimethy aminobenzaldehyde in amyl alcohol).

Kovac's reagent, which is yellow, reacts with indole and produces a red color on

the surface of the test tube

(+)= Formation of a pink to red color (“cherry-red ring”) in the reagent layer on top of
the medium within seconds of adding the reagent.

(-)= No color change even after the addition of appropriate reagent.

General Microbiology & Immunology (PM 401) Practical note Page 107