Overview

The indole is a compound that is produced by means of the reductive deamination of the tryptophan and this reaction is carried out by bacteria that have enzymes that are called tryptophanase overall. To detect the production of indole the tryptophan broth medium is used and the test is read using the Kovacs reagent (isoamyl alcohol, p-dimethylaminobenzaldehyde and concentrated hydrochloric acid) with which the indole produced reacts and produces a deep pink color.

Carrying out the practical

The liquid culture medium is inoculated with bacteria of the strain under analysis using the inoculation loop.

It is incubated at 37ºC for 24 hours and after incubation, a few drops of the Kovacs reagent are added.
If indole has been produced a fuchsia pink ring on the surface of the culture broth will appear.

Add Kovacs reagent Laura Blanes & Mariví Estevan 2022-23	Negative indole	Positive indole

Positive indole test Miguel Cerón Chulia 2021-22

Apoyo a acciones de Innovación Docente – Vicerrectorado de Estudios / Consultas e incidencias técnicas- Tlf: 96 522 2059 –