Niacin test
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The niacin test has been widely used since the 1960s to identify mycobacteria at the species level in the clinical laboratory.[1] The niacin test detects niacin (nicotinic acid) in aqueous extracts of a culture. M. tuberculosis strains that test negative for the niacin test are very rare.[2] Redox reactions happening in Mycobacterium species produce niacin as a part of energy metabolism. Even though all mycobacteria produce niacin, M. tuberculosis accumulates an excess of niacin because of its inability to process niacin, excreting the excess niacin into the culture media, thus allowing it to be detected using the niacin test.[3] The niacin test is typically only conducted on slow-growing, granular, tan colored colonies, as these are the morphology characteristics of M. tuberculosis on an agar plate.[4] Because of its affordability compared to expensive identification methods like pyrosequencing or MALDI-TOF MS that require expensive machines and reagents.[5]
