F10322 FilmTracer™ calcein green biofilm stain is an esterase substrate (Calcein AM) that has utility as a biofilm stain. The stain is non-fluorescent until non-specific esterases hydrolyze the acetoxymethyl ester producing a green-fluorecent calcein. This esterase substrate has been shown to be converted by Staphylococcus epidermidis, suggesting that the bacteria are all actively producing esterase.