Indole Test Protocol
- Author: Maria P. MacWilliams1
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VIEW AFFILIATIONS HIDE AFFILIATIONSAffiliations: 1: Department of Biological Sciences, University of Wisconsin-Parkside, Kenosha, WI, 53144-2000
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Citation: Maria P. MacWilliams. 2009. Indole test protocol.
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Publication Date : December 2009
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Category: Protocol

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Figure 1
FIG. 1. Uninoculated tryptone medium. Tryptone medium is a liquid medium that can be used to screen for tryptophanase activity via the indole test. (Maria MacWilliams, University of Wisconsin-Parkside, Kenosha)

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Figure 2
FIG. 2. The positive result of an indole test in tryptone broth done on Escherichia coli. The red reagent layer indicates the presence of indole, a by-product of tryptophan metabolism. The culture was incubated for 48 hours at 37°C. Several drops of Kovács reagent (p-dimethylaminobenzaldehyde) were added. This chemical reacts with the indole in the culture to produce the red product, rosindole. (Maria MacWilliams, University of Wisconsin-Parkside, Kenosha)

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Figure 3
FIG. 3. The negative result of an indole test in tryptone broth done on Enterobacter aerogenes. The Kovács reagent does not change color when added to the culture; it appears as a thin, yellowish liquid on the surface of the bacterial culture. The culture was incubated for 48 hours at 37°C prior to the addition of the detection reagent. (Maria MacWilliams, University of Wisconsin-Parkside, Kenosha)