Indole (Tryptophan Degradation) Test

In the Indole test, we can determine the ability of our bacteria to split the amino acid tryptophan into indole and pyruvic acid.

We first used the aseptic technique to inoculate the tryptone broth tube with a loopful of bacteria from our agar slant culture. 

Then we incubated the inoculated tube at 35 degrees Celsius for 2 days. 

When we came back after two days we added 5 drops of Kovac's reagent to the inoculated tube.

As you can see there is a darker yellow that has formed on top of the lighter yellow broth. This means that the test came out negative. Therefore, our bacteria are not able to split the amino acid tryptophan into indole and pyruvic acid.