A positive indole test indicates that a bacterium can do what?

A positive indole test indicates that a bacterium can break down tryptophan into indole. This biochemical reaction involves the enzymatic conversion of tryptophan, an amino acid found in various proteins, into indole, along with other products. The presence of indole can be detected using specific reagents, which result in a distinct color change, indicating that the organism possesses the enzyme tryptophanase.

The ability to use tryptophan as a source of carbon and nitrogen is significant for identifying various bacterial species, especially within the family Enterobacteriaceae. This test is commonly used in microbiology labs to differentiate members of this family, as not all bacteria can produce indole from tryptophan. The reaction showcases the metabolic capabilities of the organism and provides insights into its biochemical pathways.