Hydrogen peroxide is often used in microbiology for its ability to break down into water and oxygen gas. This reaction is catalyzed by the enzyme catalase, which is present in many aerobic and facultatively anaerobic bacteria. A small amount of hydrogen peroxide is added to a bacterial culture to detect the presence or absence of catalase activity in the culture. If catalase is present, it will catalyze the breakdown of the hydrogen peroxide, resulting in the formation of oxygen gas bubbles. This reaction can be visually observed as effervescence in the culture.
The absence of bubbles indicates that catalase is not present in the culture. The catalase test is commonly used in microbial identification and differentiation, as different species of bacteria present varying levels of catalase activity. For example, Staphylococcus species exhibit high levels of catalase activity, while Streptococcus species do not. The catalase test is also used to differentiate between aerobic bacteria that produce oxygen as a by-product (which typically exhibit catalase activity) and facultative anaerobic bacteria that utilize oxygen but do not produce it as a by-product (which may or may not exhibit catalase activity).
