Auramine O is a diarylmethane dye used as a fluorescent stain. In its pure form, Auramine O appears as yellow needle crystals. It is very soluble in water and soluble in ethanol.Auramine O is used for the staining of acid-fast organisms, coccidia. Auramine O along with carbol generates brilliant yellow fluorochrome of tubercle bacilli. It is effective in detecting positive cases of tuberculosis. Auramine O binds to the mycolic acid in the bacterial cell wall.