Catalase is the enzyme that breaks hydrogen peroxide (H2O2) into H2O and O2. Hydrogen
peroxide is often used as a topical disinfectant in wounds, and the bubbling that is seen is due to
the evolution of O2 gas. H2O2 is a potent oxidizing agent that can wreak havoc in a cell; because
of this, any cell that uses O2 or can live in the presence of O2 must have a way to get rid of the
peroxide. One of those ways is to make catalase.
PROCEDURE
a. Place a small amount of growth from your culture onto a clean microscope slide. If using
colonies from a blood agar plate, be very careful not to scrape up any of the blood agar—
blood cells are catalase positive and any contaminating agar could give a false positive.
b. Add a few drops of H2O2 onto the smear. If needed, mix with a toothpick. DO NOT use
a metal loop or needle with H2O2; it will give a false positive and degrade the metal.
c. A positive result is the rapid evolution of O2 as evidenced by bubbling.
d. A negative result is no bubbles or only a few scattered bubbles.
e. Dispose of your slide in the biohazard glass disposal container. Dispose of any
toothpicks in the Pipet Keeper.
OXIDASE TEST