This test distinguishes bacteria that produce the enzyme catalase, such as staphylococci, from bacteria that do not produce catalase, such as streptococci.
Principle
Catalase aids in the conversion of hydrogen peroxide to oxygen and water by acting as a catalyst. When an organism is exposed to hydrogen peroxide, it is tested for catalase production. If the organism produces catalase, oxygen bubbles are released. It's best if the culture isn't older than 24 hours.
Because catalase is present in red cells, caution should be exercised when analyzing an organism cultivated on a medium containing blood. A false positive result will arise if some of the blood agar is removed with the colony. As a result, catalase testing is commonly done on nutrient agar, which is a blood-free culture medium.
Requirements for catalase test
Hydrogen peroxide( 3% H2O2)
Glass slide
Bunsen burner
Inoculating wire loop
It's a good idea to shake the reagent before using it to get rid of any dissolved oxygen. If the hydrogen peroxide contains dissolved oxygen, false positive reactions can occur.
PROCEDURE
Pour 2-3ml of the hydrogen peroxide solution into a test tube.
• Using a sterile wooden stick or a glass rod, remove a good growth of the test organism and immerse it in the hydrogen peroxide solution.
• Look for immediate bubbling.
Results
Active bubbling indicates a positive result
No release of bubbles — no results
Note: if the organism has been cultured on an agar slope, pour
about 1ml of the hydrogen peroxide solution over a good growth of the organism, and look for the release of bubbles.
Caution: performing the test on a slide is not recommended because of the risk of contamination from active bubbling.
If the rapid slide technique is used, the hydrogen peroxide solution should be added to the organism suspension after placing the slide in a petridish. The dish should then be covered immediately, and the preparation observed for bubbling through the lid.
CONTROLS
Staphylococcus species serve as a positive catalase control. Streptococcus species as a negative catalase control.
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