What is this medium used for? Bacteria are identified based largely on what organic compounds they can break down. The range of compounds used depends on the collection of enzymes a species of bacteria can make. Tryptophan is an amino acid that some bacteria can use for carbon and energy. Tryptone broth is rich in tryptophan, and thus serves as an excellent medium to use for testing for tryptophan digestion. As some bacteria digest tryptophan, one product sometimes produced is indole, a compound responsible for the smell of feces. Tryptone broth is frequently used for the indole test, important for identifying enteric bacteria.
How is indole production determined? If indole is produced, it will accumulate in the culture tube during a 24-hour incubation. Addition of an appropriate chemical called Kovac’s reagent generates a cherry red ring floating atop the culture if indole is present in the culture.
What is the content of this medium? Tryptone broth is a nutrient broth consisting of 1% tryptone in distilled water. Tryptone is a stable product of protein digestion, and so is rich in amino acids…particularly tryptophan.
How is the test performed? For information on how to determine the ability of a microbe to use tryptone broth and produce indole, refer to the Indole production test.