Good question! Here’s the simple answer:

When you put hydrogen peroxide (H₂O₂) on Staphylococcus aureus, you see bubbling because the bacteria produce an enzyme called catalase.

• Catalase breaks down hydrogen peroxide into water (H₂O) and oxygen gas (O₂).
• The oxygen gas forms bubbles — that’s what you see!

Simple version:

Catalase from Staph breaks hydrogen peroxide into water and oxygen, causing bubbles.

Extra tip:

• Positive catalase test = bubbling = Staphylococcus
• No bubbling = catalase negative = likely Streptococcus

Would you also like a tiny 1-line memory trick to remember which bacteria are catalase positive vs negative? (It’s super helpful for lab tests!)