Ivy Tech Microbiology Lab Test 2 Practice

A positive nitrate reduction test is indicated by which observation after reagents are added?

No color change Red color after adding reagents Yellow color Purple color

Correct Answer:

Red color after adding reagents

Explanation:

Nitrate reduction is detected by the formation of nitrite, which the reagents produce a red azo dye with. If the organism has reduced nitrate to nitrite, adding the detection reagents will yield a red color, indicating a positive test. If no color appears after adding the reagents, there may be no nitrite yet or the nitrite has been reduced further; a follow-up zinc step can differentiate these possibilities, but the observation after the initial reagents is red when the test is positive.

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