Discussion
A bacterium is found to lack catalase, peroxidase and superoxide dismutase. Which of the following statements best describes this bacterium ?
Answer: C
The bacterium is an obligate anaerobe.
Whenever a cell uses oxygen, toxic by-products form: superoxide radicals and hydrogen peroxide. Superoxide dismutase converts superoxide to hydrogen peroxide, and catalase and peroxidase destroy the peroxide. An organism lacking all three cannot detoxify these species, so it can survive only where oxygen is absent.
An obligate aerobe must have these enzymes, since it lives on oxygen. 'Does not produce superoxide' gets the cause backwards: superoxide forms on exposure to oxygen whatever the enzymes, and the lack of enzymes is what makes oxygen lethal. Nothing about these enzymes indicates virulence.
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