A red color developing after the addition of Kovacs reagent in a SIM tube indicates the presence of which enzyme?

The development of a red color after the addition of Kovacs reagent in a SIM (Sulfide Indole Motility) tube indicates the presence of the enzyme tryptophanase. This enzyme facilitates the conversion of the amino acid tryptophan into indole, which then reacts with Kovacs reagent. The specific interaction between indole and Kovacs reagent leads to the formation of a red-colored complex.

Understanding the role of tryptophanase in this reaction is essential. Tryptophanase is produced by certain bacteria that can metabolize tryptophan as a nitrogen and carbon source, and the presence of this enzyme is a key biochemical marker for those microorganisms that can utilize tryptophan effectively. The red color is a direct indicator in the SIM medium that these bacteria can produce indole from tryptophan, confirming their metabolic capabilities.

This identification method is particularly useful in microbiology for differentiating and classifying various bacteria based on their enzymatic activities.