Question

?? Which of the following would be true for a negative nitrate reduction test? The nitrate broth remains clear after the addition of both reagents A and B and then zinc The nitrate broth turns red after the addition of reagents A and B. The nitrate broth remains clear after the addition of reagents A and B but turns red after the addition of zinc. The nitrate broth turns red before the addition of the reagents A and B and then zinc. I

Answer 1

The correct option is the third one

Nitrate reduction test is used to check production or presence of nitrate reductase enzyme on the medium. This test uses two reagents. reagent A ( sulfanilic acid) and reagent B ( alpha nephthyl amine). The red colour appears during positive rest. The red colour appears due to protonsil formation, Protonsil is formed when reagent B reacts with nitrite sulfanilic acid. Nitrite is found in the solution only of nitrate is being reduced to nitrite by nitrate reductase. If nitrate reductase is not preset then nitrite will not be produced and red colour will not appear ( no protonsil formation).

But always remember- Not appearence of red colour after addition of reagent A and B in the nitrate broth is not negative result. This result is not conclusive yet.

Later on we add zinc powder to make result conclusive- If solution turns red/pink after zinc powder addition then the result is confirm negative

If solution remains colourless even after addition of zinc powder then result is positive.

The first statement is incorrect- as if the solution remains colourless after addition of reagent A and B then the result is not confirm yet ( inconclusive). This result is not negative

The second statement is incorrect- If solution turns red after addition of reagent A and B then the result is nitrate reductase positive.

The fourth statement is incorrect as if nitrate broth turns red before addition of reagent A and B then it means there is experimental error and it is showing false result (positive)

Answer 2

The correct option is the third one

Nitrate reduction test is used to check production or presence of nitrate reductase enzyme on the medium. This test uses two reagents. reagent A ( sulfanilic acid) and reagent B ( alpha nephthyl amine). The red colour appears during positive rest. The red colour appears due to protonsil formation, Protonsil is formed when reagent B reacts with nitrite sulfanilic acid. Nitrite is found in the solution only of nitrate is being reduced to nitrite by nitrate reductase. If nitrate reductase is not preset then nitrite will not be produced and red colour will not appear ( no protonsil formation).

But always remember- Not appearence of red colour after addition of reagent A and B in the nitrate broth is not negative result. This result is not conclusive yet.

Later on we add zinc powder to make result conclusive- If solution turns red/pink after zinc powder addition then the result is confirm negative

If solution remains colourless even after addition of zinc powder then result is positive.

The first statement is incorrect- as if the solution remains colourless after addition of reagent A and B then the result is not confirm yet ( inconclusive). This result is not negative

The second statement is incorrect- If solution turns red after addition of reagent A and B then the result is nitrate reductase positive.

The fourth statement is incorrect as if nitrate broth turns red before addition of reagent A and B then it means there is experimental error and it is showing false result (positive)