Question

Name the test that differentiates between Staphylococcus spp. and Streptococcus spp. What is the chemical mode of action for this test? Write the chemical equation

Answer 1

Catalase test is used to differentiate between Staphylococcus spp. and Streptococcus spp.

staphylococci gives positive catalase test, while streptococci are gram negative.

Chemical mode of action for this reaction is reduction reaction.

Catalase positive bacteria contain flavoproteins . These flavoproteins reduce oxygen(O₂), resulting in production of hydrogen peroxide (H₂O₂). These substances are formed when bacteria undergo aerobic respiratory pathway where oxygen is the final acceptor of electron. The products formed in this reaction are very toxic for the bacteria. bacteria must posses enzyme that will protect it from these toxic substances. Some bacteria (facultative anaerobes & obligate aerobes) contain enzymes superoxide dimutase , catalase or peroxidase, which catalyze the destruction of these toxic substances as follows:

Superoxide dismutase 202 2H+ 02H202 Oxygen Hydrogen peroxide

Catalase 2 H20 02 2 H202 Water Free Oxygen Peroxidase

This test is done by adding hydrogen peroxide to an incubated culture. Organism that produce catalase enzyme (staphylococci)  will result in the breakdown of hydrogen peroxide to O₂ indicated by bubble production in the reagent drop, giving catalase test positive. organisms which lack catalase enzyme like streptococci, give catalase test negative.

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