Simultaneous fluorescent gram staining and activity assessment of activated sludge bacteria

Results show that staining with the fluorescent dye hexidium iodide measures Gram status with both gram-positive and gram-negative bacterial levels ranging from 1.5% in activated sludge flocs to 16% in the activated sludge fluid. The method enables a rapid, quantitative determination of Gram status linked with in situ activity of the bacterial populations within wastewater systems.