Auramine O can be used to stain acid-fast bacteria (e.g. Mycobacterium, where it binds to the mycolic acid in its cell wall) in a way similar to Ziehl-Neelsen stain. It can also be used as a fluorescent version of Schiff reagent.
Auramine O can be used together with Rhodamine B as the Truant auramine-rhodamine stain for Mycobacterium tuberculosis. It can be also used as an antiseptic agent.