The
Ziehl–Neelsen stain, also known as the
acid-fast stain, was first described by two German doctors: the bacteriologist
Franz Ziehl (1859–1926) and the pathologist
Friedrich Neelsen (1854–1898). It is a special bacteriological stain used to identify
acid-fast organisms, mainly
Mycobacteria.
Mycobacterium tuberculosis is the most important of this group because it is responsible for
tuberculosis (TB). Other important Mycobacterium species involved in human disease are
Mycobacterium leprae,
Mycobacterium kansasii,
Mycobacterium marinum,
Mycobacterium bovis,
Mycobacterium africanum and members of the
Mycobacterium avium complex. Acid fast organisms like Mycobacterium contain large amounts of lipid substances within their cell walls called mycolic acids. These acids resist staining by ordinary methods such as a
Gram stain. It can also be used to stain a few other bacteria, such as
Nocardia. The reagents used are Ziehl–Neelsen
carbol fuchsin, acid alcohol, and
methylene blue. Acid-fast bacilli will be bright red after staining.