MycoLight? Flow Cytometric Live Bacteria Assay Kit. The MycoLight Flow Cytometric Live Bacteria Assay Kit provides an easy and convenient methodfor evaluating bacterial vitality as a function of the intracellular esterase activity. MycoLight? 520 is non-fluorescent esterase substrate that diffuse into both Gram positive and Gram-negative bacteria. Upon hydrolysis by bacterial intracellular non-specific esterase, a green fluorescent product is produced and accumulated within bacteria. Compared to the commonly used esterase substrate CFDA and CFDA-AM, this kit provides brighter and more stable signal with lower background and easier staining protocol.