Day 3 - Degradation of Amino Acids

Indole (Tryptophan Degradation) Test

This test determines whether our bacteria splits the amino acid tryptophan into indole and pyruvic acid.  This splitting of the amino acid is a source of energy.

Materials:

Tryptone broth tube

Pure culture of our bacteria in a broth tube

Kovac's reagent in a dropper bottle 

Disposable gloves

Steps: 

1.  Label the tryptone broth tube with our group number and type of test.

2.  Use aseptic technique to inoculate the tyrptone broth tube from our bacterial broth tube.

3.  Incubate the inoculated tube at 35 degrees for 24-48 hours.

4.  Place 5 drops of Kovac's reagent on the culture.  A quick appearance of a red layer would be a positive result.

5.  Discard the tube properly.

Result:


Discussion:  Our bacteria gave a negative result, so it does not degrade tryptophan for energy use.  We incubated the bacteria longer to confirm this result.