This document summarizes the indole test used to identify bacteria. The indole test determines if a bacterium can produce indole from tryptophan breakdown. Materials needed include Kovac's reagent, peptone broth, an inoculating loop, and burner. Bacteria are inoculated into peptone broth and incubated. Kovac's reagent is then added - a red ring indicates indole production and identifies bacteria like E. coli, while a yellow ring indicates no indole production for bacteria such as Salmonella and S. aureus.

1. Presentation Topic
INDOLE TEST
Name :Adnan adil Department: BMLT Roll No:21BMLT002

2. Content:
Sr. No. Content
1. Material Required
2. Introduction
3. Principle
4. Procedure
5. Limitations
6. Results

3. Material Required:
1. Kovac’s Reagent ( p-dimethylaminobenzaldehyde )
2. Peptone Broth
3. Inoculating Loop
4. Burner
Introduction : Early 1889, the indole test was used as a
means of distinguishing between E-coli and
Enterobacter aerogene.

4. Principle: The indole test determines the ability of an
organism to produce indole from the breakdown of the amino
acid tryptophan. Tryptophan is hydrolyzed by tryptophanase to
produce three possible products: indole, pyruvate
and ammonium ion :
Indole test reaction

5. Methods:
 Tube Methods:- Most conventional method widely used.
 Spot Indole Test
Procedure:-
Conventional tube method-
1. Inoculate the peptone broth with the organism to be tested and incubate at 37 ° C for 18 to 24
hours.
2. Add 0.5 ml (5 drops) of Kovac's reagent and shake gently.
3. Examine the top layer of liquid after about 1 min.

6. Limitsandtechnicaldevice :-
• The test tube is more sensitive then the spot test.
• If peptone broth is use instead of tryptophan broth the
batch should be checked with a positive control this is
because there are varieties of peptone broth and some are
suitable for indole production because they contain too
little tryptophan .
• The indole test results can vary with different isolates of
the same species .

7. Result:
 Indole Positive- Red coloured ring is formed near the surface of the broth . Ex:- E-coli, Proteus
vulgaris, vibrio cholerae, etc.
 Indole Negative:- Yellow coloured ring is formed near the surface of the broth. Ex:-
Pseudomonas, Salmonella, S. aureus etc

8. Reference :-
• AMERICAN SOCIETY FOR MICROBIOLOGY
• http://microbiologie-Clinique.com/indole-test-en.html