This test demonstrates the ability of certain bacteria to decompose the amino acid tryptophan to indole, which accumulates in the medium. The isolated colony of the test organism was emulsified in tryptophan broth (peptone water) and incubated at 37°C for 24 hours in ambient air. 0.5 ml of Kovac's reagent was added to the broth culture down the side of the tube and observed for color change at meniscus. The development of a -red color (benzaldehyde reagents) within 20 seconds indicates the presence of indole. A negative test is colorless or slightly yellow.
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Tryptophan Decomposition Assay
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Other organizations : University of Port Harcourt, Rivers State University
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Variable analysis
independent variables
- Incubation of the emulsified bacterial colony in tryptophan broth (peptone water) at 37°C for 24 hours in ambient air
- Color change (development of a red color) at the meniscus upon addition of Kovac's reagent to the broth culture, indicating the presence of indole
- Incubation temperature (37°C)
- Incubation duration (24 hours)
- Ambient air conditions
- Positive control: Bacterial colony that is known to decompose tryptophan to indole, resulting in a red color upon addition of Kovac's reagent
- Negative control: Bacterial colony that is known not to decompose tryptophan to indole, resulting in a colorless or slightly yellow reaction with Kovac's reagent
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