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Biology LibreTexts

3.7: Tryptone Broth

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  • Bacterial tryptophanase coverts the amino acid tryptophan into pyruvate, ammonia, and indole. The medium used to test for this enzyme is 1% tryptone in water.


    1. Obtain a tube of tryptone broth.
    2. Using an inoculating loop, swish some of your assigned organism in the broth.
    3. Incubate the tube for at least 48 hours.
    4. After the incubation period, add several drops of Kovac's reagent to the tube.


    The chemicals in Kovac's reagent react with the indole to produce a red color. In a positive test, a red layer will float at the surface of the broth.


    Indole Positive