what is the substrate of the catalase reaction why are bubbles produced in a positive test
The enzyme catalase converts hydrogen peroxide (H2O2) to water and O2. The evolution of O2 causes bubbling. Thus, catalase-positive organisms that are mixed into hydrogen peroxide will cause bubbling (catalase-negative organisms will not). This test is good for distinguishing between Gram-positive cocci in chains (catalase negative) versus Gram-positive cocci in clusters (catalase positive).