Bacteria that have the enzyme tryptophanase, can convert the amino acid, tryptophane to indole. Indole reacts with added Kovac’s reagent to form rosindole dye which is red in color (indole +).

The presence of catalase, gelatinase, oxidase, urease, for example, can be used to identify the species of bacteria. Biochemical reactions used in biochemical tests depend on the presence of such ...