Abstract
Tétrazolium compounds which may serve as indicators of dehydrogenase activity were first described by von Pechmann and Runge in 1894 with the preparation of 2,3,5-triphenyl tétrazolium chloride (TTC) as a pale yellow, water soluble, crystalline powder (100, 112). These compounds act as electron acceptors in enzyme- catalyzed oxidations, and upon reduction, undergo a color change which makes them readily acceptable as indicators of cell viability. | Since the discovery of TTC, many new compounds such as iodo— nitrotetrazolium (INT), néotétrazolium (NT), blue tétrazolium (BT), and nitro—blue tétrazolium (NBT) have been synthesized which has improved histochemical demonstration of dehydrogenases. Of these newer compounds, NBT has proved to be superior due to its successful competition with molecular oxygen for electrons and the stable visible blue formazan formed upon reduction (117). | The clinical use of NBT as a diagnostic aid was first proposed in 1967 by Baehner and Nathan (8). These investigators demonstrated the use of NBT in identifying patients with chronic granulomatous disease. They showed that leukocytes from patients with this type of disease were unable to reduce NBT to formazan in vitro as opposed to leukocytes from healthy subjects, which could reduce this tétrazolium. The specific usefulness of NBT in clinical microbiology was suggested in 1968 when Park et al. (99) proposed the NET test as a means of distinguishing bacterial infections from non-bacterial illnesses.