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BACKGROUND
Indole test is one of the important biochemical test that is done on bacterial species for detection of organism’s capability to degrade the amino acid tryptophan and form indole. It is a part of IMViC tests, which are usually a set of experiments done for enteric organism’s differentiation. Indole test is based on the principle that the bacteria breaks the amino acid tryptophan into indole and pyruvic acid by utilizing the enzyme tryptophanase. Indole is easily detected by using Kovac reagent. The reagent contains aldehyde with which indole reacts to form a red colour, that is formed as a ring on the top.
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REQUIREMENTS
Samples: Bacterial samples
Chemicals: Tryptone broth
Kovac reagent
Apparatus: Test tubes
Incubator
Inoculation tube
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PROCEDURE
Take the bacterial sample and inoculate it carefully in tryptone broth. Then incubate it at a temperature of 370C.1 To this add about some drops of the Kovac reagent. Be careful while observing without shaking the tube, as it may disturb the experiment.
If a red colour or pink colour ring is formed in the top then it is taken as indole positive and if there is no colour change after adding Kovac’s reagent, then the bacterium is indole negative.2
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CONCLUSION
Indole test not only helps in enteric bacterium differentiation but also helps in differentiating various species.
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REFERENCES
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Carricajo A, Boiste S, Thore J, Aubert G, Gille Y, Freydière AM. Comparative evaluation of five chromogenic media for detection, enumeration and identification of urinary tract pathogens. Eur J Clin Microbiol Infect Dis. 1999;18:796-803.
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Heizmann W, Döller PC, Gutbrod B, Werner H. Rapid identification of Escherichia coli by 2. Fluorocult media and positive indole reaction. J Clin Microbiol. 1988;26:2682-4.
