VPE 511: Environment and Environmental Hygiene (2+1)

COMPLETED TEST

Test For Indole

In this test 1% tryptone is used. It contains tryptophan.  

Procedure 

• 1% tryptone agar is taken in a test tube and 1 ml of water sample is added.
• The tubes are incubated at 2 different temperatures (370C and 440C) for 24 hours.
• Kovac’s reagent is added to both tubes.  

Interpretation

• In positive cases there will be a development of pink coloured ring
• E.coli reacts with tryptophan and produces indole. This reacts with Kovac’s reagent to produce pink colour.
• Pink colour production at 37⁰C indicates presence of mildly pathogenic E.coli
• Pink colour production at 44⁰C indicates presence of highly pathogenic E.coli.