BIOCHEMICAL TEST

Indol

Indol test is a biochemical test which are performed for the detection of bacterial species which are having the ability of converting the amino acid tryptophan and producing indol. Accessed:12-12-16

Principle of test:

Some bacteria have an enzyme tryptophanase .This enzyme have the ability to split amino acid tryptophan and pyruvic acid and produce the indole. The presence or production of indole can be detected by the Kovac’s reagent or by the Ehrlich’s reagent which gives red colour ring on the top of media tube. Accessed:12-12-16

Procedure

1- Make the suspension of bacterium to be tested in distilled water and pour into typtone broth.

2- Incubate for 24 hours at 37°C.

3- After incubation add few drops of Kovac’s reagent into tube containg broth and bacterium.

Ehrlich reagent is more sensitive for non, fermentors and anaerobes.

4- Observe the result carefully and avoid to shaking the tube. Accessed:12-12-16

Result:

Red or pink color on the top indicated as the Positive test. Figure 2

No change will be resulted as Negative result. Figure 1

Accessed:12-12-16

Shows Negative Indol Test

Shows Positive Indol Test