Catalase Test

Catalase Test

Short review
The bacteria produce hydrogen peroxide (H2O2) during their aerobic respiration, and if it accumulates inside the bacterial cells, it’s too toxic, so usually most bacteria (aerobic & facultative anaerobic) will utilize this enzyme to degrade H2O2.

Principle
The enzyme catalase mediates the breakdown of hydrogen peroxide into oxygen and water. The presence of the enzyme in a bacterial isolate is evident when a small inoculums is introduced into hydrogen peroxide (3% solution), and a rapid elaboration of oxygen bubbles occurs. The lack of catalase is evident by a lack of or weak bubble production.

Method
• Use sterile wooden stick to transfer a small amount of colony growth to the surface of a clean, dry glass slide.
• Place a drop of 3% hydrogen peroxide (H2O2) onto the inoculums.
• Observe for the evolution of oxygen bubbles.

Expected Results
Catalase-positive organisms (e.g., staphyloccoci, Listeria monocytogenes, and corynebacterium spp.) produce copious bubbles; catalase-negative organisms (e.g., streptococci and enterococci) yield no or few bubbles.
Note: some bacteria produce peroxides that slowly catalyzes the breakdown of (H2O2) and the test may appear weakly positive (a few bubbles slowly elaborated). This reaction is not a truly positive test and is considered negative.

Notes to be observed
1- Don’t use media containing blood, because the red blood cells contain Catalase and it will give us a false positive test.

2-Always use a fresh H2O2 because it’s unstable and check it via a control known strain of a Catalase positive one.

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