The indole (modified Kovacs' reagent) is used to assess the ability of certain bacteria to...

The indole (modified Kovacs' reagent) is used to assess the ability of certain bacteria to produce indole by the deamination of tryptophan. Indole reacts with aldehyde in the Kovac's reagent to produce a red color. An alcoholic layer holds the red color as a ring at the top of the tube used for the idole test.

If a bacteria produces the enzyme tryptophanase to break down the amino acid tryptophan, which of the following tests will be positive with Kovac's reagent?