A simple, rapid method for enumerating total viable and metabolically active bacteria in groundwater.

We report here a new staining procedure which uses both the enzymatic dehydrogenation of 2-(p-iodophenyl)-3-p-(nitrophenyl)-5 phenyltetrazolium chloride to a pink intracellular formazan and the DNA-specific fluorochrome 4',6'-diamidino-2-phenylindole. Application of this staining procedure to cells concentrated on filters and then transferred to microscope slides by the filter-transfer-freeze technique has proven valuable for statistically accurate enumeration of the total viable and metabolically active cells in groundwaters.