The catalase test is a biochemical test used by microbiologists to identify species of bacteria (whether they possess catalase). It requires the adding of a few drops of 3% hydrogen peroxide directly to the young broth culture or colonies on agar surface or clumps of cells on glass surfaces to determine the presence of catalase in the organisms. Catalase is a common enzyme found in nearly all living organisms which are exposed to oxygen (Aerobic organisms). Obligate Anaerobes do not have catalase as they do not use oxygen in their respiration.
Catalase catalyses the decomposition of hydrogen peroxide to water and oxygen according to the equations:
O2- → O2 + 2H2O
Superoxide dismutase
2H2O2 →2H2O + O2
Catalase Test -
Materials :
- 24 hours trypticase soy agar plate of Staphylococcus aureus and Streptococcus faecalis.
- 3% hydrogen peroxide solution.
- Droppers
Procedures :
- Add 2 to 3 drops of 3% hydrogen peroxide solution onto isolated bacterial colonies.
- Observe and look out for any effervescences produced.
Results :
A Positive test is indicated by the production of gas bubbles or the presence of effevescence. Staphylococci and micrococcus are examples of genus of catalase-positive bacteria.
The white bubbles are oxygen gas produced from hydrogen peroxide.
The catalase test is Negative if there is no effervascence formed. Streptococci and enterococci are examples of genus of catalase-negative bacteria.
Streptococcus species is an example of aerobic bacteria that do not possess catalase. Catalase has also been observed in some anaerobic microorganisms, such as Methanosarcina barkeri. Thus, not all aerobes possess catalase and anaerobes do not possess catalase.