What indicates a positive catalase test?

• A. Color change to blue
• B. Bubbling when hydrogen peroxide is added to the culture.
• C. Growth inhibition
• D. No reaction

Answer: (B)

Catalase works by breaking down hydrogen peroxide into water and oxygen. A positive catalase test is shown by rapid bubbling when hydrogen peroxide is added to the culture, because the enzyme releases oxygen gas as it acts. This visible effervescence is the clear sign that catalase is present. A blue color change is not related to catalase activity; that kind of color change is seen in other tests (for example, oxidase or certain indicator-based assays). Growth inhibition describes effects on growth from other factors and isn’t about the enzymatic breakdown of peroxide, and no reaction would mean catalase is not present.