In the SIM medium test, what reagent must be added to detect tryptophan hydrolysis (indole production) by bacteria?

• A. Kovac's reagent
• B. Barritt's reagent
• C. Crystal violet
• D. Methyl red

Answer: (A)

Verified step by step guidance

1. Understand the purpose of the SIM medium test: it is used to detect sulfur reduction, indole production, and motility in bacteria.
2. Focus on the indole production part, which tests whether bacteria can hydrolyze tryptophan to produce indole.
3. Recall that to detect indole, a specific reagent is added after incubation to react with indole and produce a visible color change.
4. Identify the reagent used for this detection: Kovac's reagent is commonly added to the SIM medium to detect indole by forming a red layer on top if indole is present.
5. Note that other reagents listed, such as Barritt's reagent, Crystal violet, and Methyl red, are used for different biochemical tests and are not appropriate for detecting indole in the SIM test.