Catalase Test

Most aerobic and facultative aerobic bacteria that utilize oxygen produce hydrogen peroxide. Their electron transport system transfers electrons from reduced flavoprotein to oxygen, yielding oxidized flavoprotein and hydrogen peroxide. Hydrogen peroxide is toxic to the enzymatic function of the bacteria. Survival in the midst of this antimetabolite is feasible due to the production of catalase, an enzyme which converts hydrogen peroxide to water and oxygen. Once an unknown bacterium is isolated on a slant, catalase production can be ascertained. A slide is sterilized with 70% ethanol and a small circle is drawn on it using a wax pencil. A drop of hydrogen peroxide is placed in this circle. Using aseptic technique, a small visible aliquot of bacterial cells are removed from the slant using an inoculating needle and transfered to the hydrogen peroxide. If the hydrogen peroxide begins to bubble, the bacteria is attempting to break down the hydrogen peroxide through the release of catalase. This is an indication of a catalase positive test. The bacteria is literally struggling to save its life. Anaerobic bacteria such as streptococcus, enterococcus, and lactobacillus, that live in an unoxygenated environment do not produce such peroxide degraders. Most organisms which thrive in oxygenated environment produce catalase to degrade hydrogen peroxide.