For reliable results, the niacin test should be performed only from cultures that are at least:
a. 2 weeks old and show at least five colo-nies on Löwenstein-Jensen medium.
b. 3 weeks old and show at least 50 colonies on Löwenstein-Jensen medium.
c. 3 weeks old and show at least 50 colonies on Middlebrook 7H11 agar.
d. 2 weeks old and show at least five colo-nies on Middlebrook 7H11 agar.
B
Niacin (nicotinic acid) plays an important role in the oxidation-reduction reactions that occur during mycobacterial metabolism. For reliable results, the niacin test should be performed only from cultures that are at least 3 weeks old and show at least 50 colonies on Löwenstein-Jensen medium; otherwise, adequate niacin may not be produced to be detected.
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