Principle of Indole test The ability of an organism to split Indole from the amino acid tryptophan is due to the presence of tryptophanase. Indole, if present, combines with the aldehyde in the reagent to produce a pink to red-violet quinoidal compound (benzaldehyde reagent). The enzyme tryptophanase catalyzes the deamination reaction by attacking the tryptophan molecule in its side chain and leaving the aromatic ring intact in the form of Indole. #petridish #microbiology #microbiologist #microb