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Success! In Clinical Laboratory Science – Bacteriology Practice Test

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Which of the following is catalase negative?
Correct Answer:
Leuconostoc
Explanation:
The main idea being tested is whether an organism has the catalase enzyme, detected by the catalase test. When you apply hydrogen peroxide to a colony, bubbles indicate catalase activity because the enzyme rapidly breaks down hydrogen peroxide into water and oxygen; no bubbles mean the organism is catalase negative. In this set, Bacillus, Corynebacterium, and Listeria all produce catalase, so they will show bubbling. Leuconostoc, on the other hand, does not produce catalase, so there is no bubbling. This makes Leuconostoc catalase negative, which helps distinguish it from the other organisms in identification workflows.

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