Indole production by organisms is observed by inserting the Kovac's reagent strip between the plug and inner wall of the tube, above the inoculated Peptone Water (TM 330) and incubating at 35-37°C for 18-24 hours. Preparation of Kovac's reagent Kovac's reagent is prepared by dissolving 10 gm of p-dimethyl amino benzaldehyde in 150 ml of isoamyl alcohol and then slowly adding 50 ml of concentrated hydrochloric acid
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 (1). The presence of indole is detected by the Kovac's reagent strip which turns pink in the presence of indole. Kovac's Reagent Strips are sterile filter paper strips impregnated with Kovac's reagent. Peptone is used in the preparation of Peptone Water because of its high tryptophan content. When tryptophan is degraded by bacteria, indole is produced. Tryptone Water (TM 392) can also be used to detect indole production in the identification of members of coliform group (2).