Hydrogen peroxide (H2O2) is generated as an oxidative by-product of aerobic carbohydrate metabolism, but it is toxic to bacteria. Many aerobic and facultative bacteria produce enzymes such as catalase, which breaks down hydrogen peroxide to oxygen and water.
Reagents:
(1) 3% hydrogen peroxide, refrigerated and stored in a brown bottle
Test material:
(1) pure culture of an isolate, 18 to 24 hours old
Procedure:
(1) a sample of a bacterial colony is transferred to a glass slide
(2) a drop of hydrogen peroxide is added to the sample
(3) positive and negative controls should give expected results
Interpretation:
• Generation of abundant bubbles indicates the presence of catalase activity.
• True negative results are seen with Streptococcus species and anaerobic bacteria.
• True positive results are seen with many clinical isolates.
Causes of a false negative result:
(1) degraded hydrogen peroxide reagent
Causes of a false positive:
(1) mixed culture
(2) red blood cells (contain catalase)
(3) enzymes other than catalase (usually show only weak activity)
