Catalase Test

Question 1

Purpose of catalase test :

Answer 1

This test differentiates catalase-positive micro- coccal and staphylococcal species from catalase-negative streptococcal species.

Question 2

Principle of catalase test :

Answer 2

Aerobic and facultative anaerobic organisms produce two toxins during normal metabolism, hydrogen peroxide (H₂O) and superoxide radical (02-). These bacteria have two enzymes that detoxify the products of normal metabo lism. One of these enzymes, catalase, is capable of converting hydrogen peroxide to water and oxygen. The presence of the enzyme in a bacte rial isolate is evidenced when a small inoculum introduced into hydrogen peroxide (30% for the slide test) causes rapid elaboration of oxygen bubbles. The lack of catalase is evident by a lack of or weak bubble production

Question 3

Method of catalase test :

Answer 3

1. Use a loop or sterile wooden stick to transfer a small amount of colony growth to the surface of a clean, dry glass slide
2. Place a drop of 30% hydrogen peroxide (H₂O) onto the medium.
3. Observe for the evolution of oxygen bubbles

Question 4

Expected results of catalase test :

Answer 4

Positive: Copious bubbles are produced

Negative: No or few bubbles are produced

Question 5

Limitation of catalase test :

Answer 5

Some organisms (enterococci) produce a per oxidase that slowly catalyzes the breakdown of HO,, and the test may appear weakly positive. This reaction is not a truly positive test.

False positives may occur if the sample is contaminated with blood agar

Question 6

Quality control of catalase test:

Answer 6

Positive: Staphylococcus aureus

Negative: Streptococcus pyogenes