Kovac's Reagent Strips are used to detect indole producing bacteria. The various enzymes involved in the degradation of tryptophan to indole are collectively called as tryptophanase, a general term used to denote the complete system of enzymes. The presence of indole is detected by the Kovac's reagent strip which turns pink in the presence of indole. Escherichia coli ATCC 25922:Positive reaction, pink colour at the lower portion of the strip. Enterobacter aerogenes ATCC 13048 negative reaction, no colour change.