During aerobic respiration in the presence of oxygen, microorganisms produce hydrogen peroxide (H2O2) which is lethal to the cell. The enzyme catalase present in some microorganisms breaks down hydrogen peroxide to water and oxygen and helps them in their survival. Catalase test is performed by adding H2O2 to the culture. Release of oxygen gas (O2↑) bubbles is a positive catalase test. The fresh clean glass slide was taken and a drop of H2O2 was placed at the center on glass slide. A loop full of Vibrio sp culture was placed on the H2O2 drop and the appearance of bubbles was noticed