New approaches to measuring total bacterial populations in water supplies

Direct counts of stained bacterial cells were compared with counts obtained from standard plating techniques. The method used by the authors combined acridine orange staining with 2‐(p‐iodophenyl)‐3‐(p‐nitrophenyl)‐5‐phenyl‐tetrazolium chloride reduction. To overcome the interference of a membrane filter's pores with the identification of stained cells, the authors used a gel‐stripping technique to transfer the bacterial cells from membrane filters to a gelatin matrix before counts were made. The method will supplement standard plate counts by determining metabolically active bacteria in a water sample within four hours.