What is tested in the indole test?

The indole test assesses an organism's ability to break down the amino acid tryptophan into indole, pyruvate, and ammonia through the action of the enzyme tryptophanase. This is an important metabolic test in microbiology that helps differentiate between various species of bacteria, particularly within the Enterobacteriaceae family.

When tryptophan is metabolized, indole is produced, which can be detected after adding a reagent, typically Kovac's reagent, that reacts with indole to produce a red ring at the top of the test medium. This color change indicates a positive result for the presence of indole, confirming the organism's capability to utilize tryptophan effectively.

The other options reflect different metabolic activities or characteristics of microorganisms but are unrelated to the indole test. Bile tolerance examines an organism's resistance to bile salts, sodium deoxycholate tests for a specific response to this detergent, and mannitol fermentation assesses the ability to ferment mannitol sugar. Each of these tests serves a distinct purpose in microbiological identification and does not correlate with the tryptophan breakdown evaluated in the indole test.