Fuchsin fluorescence in Mycobacterium tuberculosis: The Ziehl–Neelsen stain in a new light

Abstract Tuberculosis (TB) is often diagnosed by observation of reddish pink fuchsin-stained Mycobacterium tuberculosis (MTB) in Ziehl–Neelsen (Z–N) stained smears by transmitted light microscopy. MTB too faintly stained with fuchsin to be seen by transmitted light may be detected by their green-excited orange-red fluorescence; this finding may be clinically relevant.