Indole test

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The indole test is a simple biochemical method for the classification of bacteria ( Bunte series ). The test is used for the indirect detection of the enzyme tryptophanase . Tryptophanase splits tryptophan 1 to indole 2 , pyruvate 3 and ammonia (or ammonium ions):

Indole test reaction scheme

Indole reacts with 4- ( N , N -dimethylamino) benzaldehyde to form the red cyanine dye rosindole , which is soluble in alcohol, ether and chloroform. The indole reagent, also known as Kovacs reagent , is a solution of 5% 4- ( N , N -dimethylamino) benzaldehyde in 75% isoamyl alcohol and 25% concentrated hydrochloric acid. A bacterium is indole-positive if it turns red after adding the indole reagent. If the solution remains colorless, the bacterium is indole-negative. This test is used to differentiate and identify bacteria, especially Enterobacteriaceae, and is part of the so-called IMViC reactions.

literature

  • A. Böhme: The application of Ehrlich's indole reaction for bacteriological purposes. In: Zentralblatt für Bakteriologie, Parasitenkunde, Infectious Diseases and Hygiene. Vol. 40, 1906, pp. 133-192.
  • n. Kovacs: A simplified method for the detection of indole formation by bacteria. In: Journal of Immunology, Allergy, and Clinical Immunology. Vol. 55, 1928, pp. 311-315.
  • Hans G. Schlegel: General microbiology. 7th edition. Thieme, Stuttgart / New York 1992, ISBN 3-13-444607-3 , pp. 307-310.