Question

Which mycobacterium spp. do not produce the enzyme required to convert niacin to niacin ribonucleotide? Does the enzyme deficient state result in a niacin positive or negative test and why?

Answer 1

Most of the species of Mycobacterium can convert Niacin in to NAD (Nicotinamide Adenine Dinucleotide). But some species like Mycobacterium tuberculosis, Mycobacterium simiae do not have the enzyme which converts Niacin in to NAD. In the absence of the enzyme, they accummulate niacin. The accumulated niacin can be detected by a test. Using niacin strips, excess niacin can be detected because the tube will turn yellow if there is excess Niacin. Such yellowing due to excess niacin is considered Niacin +ve. So lack of enzyme to convert Niacin in to NAD is Niacin positive. It is positive because there is lot of Niacin accumulating due to lack of the enzyme.