Catalase Test

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Catalase Test, in this test the microbial culture from Nutrient Agar plates were used. This test determines the production of catalase by the microorganisms. Catalase is an enzyme which decomposes hydrogen peroxide to water and oxygen gas thereby, protecting the microorganisms from the lethal effect of hydrogen peroxide which is accumulated as an end product of aerobic carbohydrate metabolism. (Bahrami-Hessari et. al. 2014) The slide containing Micrococcus luteus produced bubbles when 3% hydrogen peroxide was dropped on it. (see Figure 9.3) This indicates that Micrococcus luteus produces catalase. Vigourous bubbling occurred when he slide containing the unknown microbe was dropped with 3% hydrogen peroxide. (See Figure 9.4) This indicates that the unknown microbe can produce catalase.
Nitrate Broth contains potassium nitrate as the source of nitrate. It is used to differentiate microorganisms that have the ability to reduce nitrate. Nitrate may be reduced to nitrite, ammonia, and nitrogen gas. The nitrate reduction test reagents used are, sulfanillic acid (nitrate reagent A), and
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Pyruvate can be metabolized into neutral compounds such as acetoin, 2-3 butylene glycol, and diacetyl. [2 pyruvate -> acetoin + 2CO2 ; acetoin + NADH + H+ -> 2,3-butanediol + NAD+] “In the presence of alkali (KOH) and atmospheric oxygen, acetyl methyl carbinol is oxidized to diacetyl, a reaction which is catalyzed by alpha- naphthol. Diacetyl formed reacts with guanidine-containing compounds such as arginine contributed by peptone in the medium, to form a red colored product. The resultant red color is indicative of a positive VP test.” (Pradhan, 2014) In both cultures, there is no red coloration observed (see Figure 11.6 and 11.7), thus Micrococcus luteus and the unknown microbe are both unable to produce acetoin via butanediol

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