Catalase Test
The catalase test detects catalase enzyme activity by bubbling when hydrogen peroxide is broken down into water and oxygen.
Core idea
It is a fast first branch for Gram-positive cocci, especially separating Staphylococcus-like organisms from Streptococcus/Enterococcus-like organisms.
Principle
Catalase-positive organisms produce visible bubbles after exposure to hydrogen peroxide.
Visual reactions
Catalase Branch Points
| Result | Common branch | Remember |
|---|---|---|
| Positive | Staphylococcus, Micrococcus, Bacillus, many coryneforms | Bubbling is oxygen release from peroxide breakdown |
| Negative | Streptococcus, Enterococcus, many related cocci | Use hemolysis, PYR, bile esculin, and salt tolerance next |
| Weak or questionable | May be technical or organism-dependent | Repeat with fresh growth and avoid blood agar carryover |
Basic workflow
- Use growth from a suitable non-blood medium when possible.
- Place a small amount of organism on a clean slide.
- Add hydrogen peroxide.
- Watch for immediate bubbling.
- Compare with expected controls when required.
How to read it
- Positive bubbling supports Staphylococcus, Micrococcus, Bacillus, or many coryneform possibilities.
- Negative reaction supports Streptococcus, Enterococcus, and related catalase-negative organisms.
- Weak or delayed bubbling should be interpreted cautiously.
High-yield trapCommon mistakes
- Picking from blood agar and carrying over red cells.
- Using too much organism.
- Treating catalase as an identification by itself.
ShortcutStudent shortcut
For Gram-positive cocci, catalase is the fork in the road: clusters usually positive, chains usually negative.