If a bacterium produces the enzyme tryptophanase, which test would yield a positive result with Kovacs reagent?

When a bacterium produces the enzyme tryptophanase, it is capable of converting the amino acid tryptophan into indole, among other products. The indole test specifically assesses this enzymatic activity.

When a culture is incubated with tryptophan and Kovacs reagent is added, the presence of indole will lead to the formation of a reddish ring at the top of the tube due to the reaction between indole and the Kovacs reagent, indicating a positive result. This ability to produce indole is a key characteristic used to differentiate certain bacterial species.

In contrast, the other tests listed do not directly relate to the production of indole. The methyl red test is associated with the bacteria’s ability to perform mixed acid fermentation, the citrate test evaluates the utilization of citrate as a carbon source, and the urease test assesses the organism's capability to hydrolyze urea into ammonia and carbon dioxide. Thus, these tests measure different metabolic pathways and would not yield a positive result with Kovacs reagent in the context of indole production.