Veterinary Clinical Biochemistry and Laboratory Diagnosis-II

DIAGNOSTIC METHODS

Principle

• Some bacteria and macrophages can reduce diatomic oxygen to hydrogen peroxide or superoxide.
• Both of these molecules are toxic to bacteria. Some bacteria, however, possess a defense mechanism, which can minimize the harm done by the two compounds.These resistant bacteria use two enzymes to catalyze the conversion of hydrogen peroxide and superoxide back into diatomic oxygen and water.
• One of these enzymes is catalase and its presence can be detected by a simple test.
• The catalase test involves adding hydrogen peroxide to a culture sample or agar slant. If the bacteria in question produce catalase, they will convert the hydrogen peroxide in to water and oxygen gas.
• The rapid effervescence (bubbles) indicates production of oxygen gas and is an indicative of a positive test.

Methodology

• Inoculate a nutrient agar plate with the test organism.
• Incubate at 37⁰C for 24 hours.
• Pour few drops of 3% hydrogen peroxide over the colony

Result

• In positive cases there will be immediate liberation of oxygen indicated by effervescence.

Catalase Test

Control

• Positive : Staphylococcus species
• Negative : Streptococcus species