Cell Meter? Bacterial Viability Assay Kit. AAT Bioquest's Mycolight? Bacterial Viability Assay Kit provides two-color fluorescence assay of bacterial viability in both gram-positive and negative bacterial cell. The kit utilizes the mixture of our green fluorescent nucleic acid stain MycoLight? Green and the red-fluorescent nucleic acid stain propidium iodide. When used alone, the MycoLight? Green stain generally labels all bacteria (live and dead) in a population. In contrast, propidium iodide penetrates only bacteria with damaged membranes, causing a reduction in the MycoLight? Green stain fluorescence when both dyes are present. Thus, with an appropriate mixture of the MycoLight? Green and propidium iodide stains, live bacteria with intact cell membranes emits green fluorescence, whereas dead or dying bacteria with damaged membranes gives red fluorescence. The Mycolight ? Bacterial Viability Assay Kit is a robust tool for monitoring the viability of bacterial populations as a function of the membrane integrity of the cell. Stained cells can be monitored fluorimetrically at 510-530 nm (FITC filter) and 600-660 nm (Texas red filter) with excitation at 488 nm, the most common excitation light source.