DMACA reagent is used to detect indole from Tryptophan. It is used for the rapid identification of bacteria containing tryptophanase enzyme systems.Tryptophanase present in E . coli cleaves tryptophan to indole and α -aminopropionic acid. Dimethylaminocinnamaldehyde in the reagent builds with indole a blue-purple complex. Escherichia coli ATCC 25922 Positive(blue-purple colouration around colony); Pseudomonas aeruginosa ATCC 27853 Negative(No colour change around colony)