Using dyes as a potential indicator of bacterial numbers in natural water (Enterobacter aerogenes, Escherichia coli, Enterococcus faecalis, Klebsiella pneumoniae, Salmonella typhimurium)

Resazurin (blue) irreversibly reduces to resorufin pink) and then in a reversible reversible step further reduces to dihydroresorufin (colorless). The dye, 2,6-dichloroindophenol (DCI) (blue), shows an acid-base color change (blue to red) and a disappearance of color upon reduction. Thionin (violet) has a very pronounced metachromatic property staining from blue to purplish red in dilute solution and disappearance of color on reduction. Thionin maintains the capability of reversing to its original color state (blue).; All three dyes are part of a group of dyes called quinone-imines and are further classified into different subgroups. Resazurin, 2,6-DCI, and thionin are classified in subgroups oxazins, indophenols, and thiazins, respectively. The dyes of the quinone-imine group contain two chromophore groups, the indamine group, and the quinoid benzene ring. Even though the dyes are closely related they do not react similarly.; This study was undertaken to determine if the reducible dye, 2,6-DCI, and a metachromatic dye, thionin, react similarly or better than resazurin in the estimation of bacterial numbers. The dyes were used with Enterobacter aerogenes, Escherichia coli, Enterococcus faecalis, Klebsiella pneumoniae, and Salmonella typhimurium pure cultures, mixed bacterial cultures, and natural water. (Abstract shortened by UMI.)...