Catalase Test

The catalase test is a biochemical test used to differentiate between bacteria that produce the enzyme catalase from those that do not. Catalase is an enzyme that catalyzes the decomposition of hydrogen peroxide (H2O2) into water (H2O) and oxygen (O2). The presence of catalase allows bacteria to detoxify hydrogen peroxide, which is produced by phagocytic cells as part of the immune response.

Principle:

Bacteria that produce catalase are able to break down hydrogen peroxide into water and oxygen gas.

The production of oxygen gas bubbles when hydrogen peroxide is added to a bacterial colony or suspension indicates a positive catalase reaction.

Procedure:

• Place a small amount of bacterial growth (colony or suspension) onto a clean microscope slide using a sterile inoculating loop.
• Add a few drops of 3% hydrogen peroxide solution to the bacterial growth on the slide.
• Observe the reaction for the formation of bubbles within a few seconds.

Interpretation:

Positive Result: The presence of bubbles within a few seconds indicates a positive catalase reaction, indicating that the bacteria produce catalase.

Negative Result: No bubbles or only a very slight effervescence indicates a negative catalase reaction, suggesting that the bacteria do not produce catalase.

Examples:

Catalase-positive organisms include Staphylococcus aureus, Enterococcus species, and many aerobic bacteria.

Catalase-negative organisms include Streptococcus species, Lactobacillus species, and some anaerobic bacteria.

Precautions:

• Use fresh hydrogen peroxide solution to ensure reliable results.
• Interpret the results within a few seconds after adding hydrogen peroxide, as prolonged exposure to air can lead to false-positive results due to oxygen absorption.

Clinical Significance:

The catalase test is commonly used in clinical microbiology laboratories to differentiate between catalase-positive and catalase-negative bacteria. It is particularly useful in the identification of Staphylococcus species, as Staphylococcus aureus is catalase-positive, while most other staphylococci are catalase-negative. 

Overall, the catalase test is a simple and rapid biochemical test that aids in the identification and differentiation of bacteria based on their ability to produce the enzyme catalase.