5-Cyano-2,3-di-(p-tolyl)tetrazolium chloride

5-Cyano-2,3-di-(p-tolyl)tetrazolium chloride (CTC) is a widely used and accepted dye in environmental and ecological studies. The redox dye CTC is a good vital stain for estimating aerobic bacteria with high metabolic activity due to their ability to reduce CTC to the fluorescent product. The reduction to the fluorescently active formazan form occurs by CTC scavenging for electrons from the components of the electron transport system or dehydrogenases. The dye has been used in conjunction with the nucleic acid staining dye DAPI to quantitate viable bacteria.