FM dyes are lipophilic styryl compounds used in a wide variety of studies involving plasma membrane and vesiculation. The water-soluble FM® dyes are virtually nonfluorescent in aqueous media and are believed to insert into the surface membrane where they become intensely fluorescent. FM® 1-43 stain has been used successfully to stain the cell bodies specifically in a complex biofilm mileu, including Pseudomonas aeruginosa, Escherichia coli, Staphylococcus sp., Acidothiobacillus caldus, and Vibrio cholerae.