Which enzyme's activity is detected when hydrogen peroxide is used in a microbial assay?

• A. Amylase
• B. Catalase
• C. Lipase
• D. Protease

Answer: (B)

Detecting catalase activity is what hydrogen peroxide is used for in this kind of microbial assay. Catalase protects cells from hydrogen peroxide, a toxic byproduct of metabolism, by rapidly breaking it down into water and oxygen. When you add hydrogen peroxide to a culture, an organism that makes catalase will rapidly decompose the peroxide and produce visible bubbles of oxygen. That quick bubble formation is a positive catalase test and indicates the enzyme is present.

The other enzymes listed are detected by completely different substrates and setups. Amylase is tested with starch and iodine to reveal starch breakdown, not by hydrogen peroxide. Lipase is detected by lipid-containing media where hydrolysis creates clear halos around colonies, often with emulsified fats, not through a peroxide reaction. Protease tests use protein-containing media (like casein or gelatin) to show clearing zones from protein degradation, again not involving hydrogen peroxide.

So the hydrogen peroxide–based assay specifically reveals the presence of catalase, the enzyme that converts hydrogen peroxide into water and oxygen.