Question

These quistion related to Oxidase Assay for Respiration and Catalase Assay experiment

1.In the clinical (real-world) setting, what is the main objective of performing laboratory tests such as the oxidase or catalase assays?

2.Some very important pathogens are positive for the oxidase test. Use your text or the Internet to find one such example.

3.A student performing the Experiment 2 of this lab set up a positive control with a known catalase-positive bacterium. However, he had no remaining hydrogen peroxide in his lab kit supplies so he used some that he had in his home medicine cabinet.   No bubbles were produced after the addition of the hydrogen peroxide even though the organism is catalase positive. What explanation can you give for this

Answer 1

1] The oxidase test is used to identify bacteria that produce cytochrome c oxidase, an enzyme of the bacterial electron transport chain. All oxidase positive bacteria are aerobic and can use oxygen as a terminal electron acceptor in respiration. Oxidase negative bacteria can be aerobic too [ they are anaerobic as well as facultative ]

The oxidase or catalase assays help to differentiate those aerobic bacteria which produce cytochrome c oxidase from those which do not. So, the main purpose of the test is to categorize bacteria on the basis of the presence or absence of this enzyme. The cytochrome c oxidase oxidizes the test reagent and helps to identify the oxidase positive bacteria.

2] Aerobic bacteria generally are oxidase positive. Some bacteria which are oxidase positive belong to Pseudomonas, Neisseria, Alcaligens, Vibrio, Pasteurella, Brucella etc, to name a few.

Oxidase positive bacteria contain cytochrome c oxidase and can, therefore, use oxygen to produce energy by converting O2 to H2O2 and H2O with an electron transfer chain.

3] The reason for the bubbles not appearing may be the lack of catalase in the bacteria. Catalase enzyme mediates the breakdown of H2O2 into O2 and water. The O2 is liberated as bubbles in the experimental set-up. So, if O2 is not being formed, it means there is not enough catalase to react with H2O2 and cause its breakdown.