Catalase test is done to check for the presence of enzyme catalase in bacteria that hydrolyzes hydrogen peroxide (H2O2) into water (H2O) and oxygen (O2). If the bacteria possess catalase enzyme, it’s evident by formation of bubbles in the test due to liberation of oxygen. Lack of catalase is indicated by absence of bubble production.

Catalase test
Uses of Catalase test:
  1. It is used to differentiate between genus Staphylococcus and Streptococcus. Staphylococcus possesses catalase (catalase positive) while Streptococcus lacks this enzyme (catalase negative).
  2. It is used for presumptive identification of gram negative bacilli belonging to Enterobacteriaceae family.
Procedure for Catalase test:
  1. Using a sterile loop or wooden stick, pick a small amount colony and place it onto the clean, dry glass slide.
  2. Using a dropper, place a drop of 3% hydrogen peroxide onto the organism on the microscope slide.
  3. Observe for the formation of bubbles.
Note: It’s better to perform this test from colonies grown on Nutrient agar. This is particularly important if the colony is picked from blood agar, the carryover of red blood cells into the test may result in a false-positive reaction.

Expected results for Catalase test:

Positive: Copious bubbles produced
Negative: No or few bubbles produced
Note: Enterococci produces an enzyme peroxidase that slowly catalyses the breakdown of H2O2 and the test may appear weakly positive. This reaction is not a truly positive test.
Quality Control for Catalase test:

Positive: Staphylococcus aureus
Negative: Streptococcus pyogenes

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