The reaction is based on the transfer of electrons from NADH, a product of the threonine
dehydrogenase [TDH] catalyzed reaction, to the tetrazolium dye [p-iodonitrotetrazolium
violet]. Threonine dehydrogenase [TDH] from bacteria/fungi catalyses the NAD-dependent
oxidation of threonine to form 2- amino-3-ketobutyrate and NADH. During the active growth
of bacteria/fungi, an electron is transferred from NADH [which is colourless in the visible
range] to p-iodonitrotetrazolium violet resulting in a formazan dye, which is purple in colour.
Therefore, the clear zone(s) on the chromatogram indicate areas of inhibi