Microbiology: Indole Test (Tryptophanase)

The video tutorial explains the indole test, a method used to identify gram-negative bacilli. It details the role of tryptophan and the enzyme tryptophanase in producing indole, which reacts with Kovacs reagent to produce a red color, indicating a positive result. The absence of this color suggests a negative result, meaning tryptophanase is not expressed. The tutorial provides a clear explanation of how to interpret the test results, emphasizing the simplicity and straightforward nature of the indole test.

What is the primary purpose of the indole test?

• To identify gram-positive cocci

• To identify gram-negative bacilli

• To measure bacterial growth rate

• To test for antibiotic resistance

Which enzyme is responsible for hydrolyzing tryptophan in the indole test?

• Lipase

• Amylase

• Protease

• Tryptophanase

Which reagent is used to detect indole in the indole test?

• Fehling's solution

• Biuret reagent

• Kovacs reagent

• Benedict's reagent

What color indicates a positive result in the indole test?

• Blue

• Green

• Yellow

• Red

What does a yellowish color at the top of the tube indicate in the indole test?

• Presence of indole

• Presence of ammonia

• Presence of tryptophanase

• Absence of tryptophanase