Ziehl–Neelsen stain

This staining method was initially introduced by Paul Ehrlich (1854–1915) and subsequently modified by the German bacteriologists Franz Ziehl (1859–1926) and Friedrich Neelsen (1854–1898) during the late 19th century.

[1][2] After the Ziehl-Neelsen staining procedure using carbol fuchsin, acid-fast bacteria are observable as vivid red or pink rods set against a blue or green background, depending on the specific counterstain used, such as methylene blue or malachite green, respectively.

Non-acid-fast bacteria and other cellular structures will be colored by the counterstain, allowing for clear differentiation.

[4] Mycobacterium are slow-growing rod-shaped bacilli that are slightly curved or straight, and are considered to be Gram positive.

These acid-fast organisms like Mycobacterium contain large amounts of lipid substances within their cell walls called mycolic acids.

Narrow spectrum fungal stains are selective, and they can help differentiate and identify fungi.

[16][17] Some free endospores can be confused with small yeasts, so staining is used to identify the unknown fungi.

[20] Franz Ziehl then altered Ehrlich's staining technique by using carbolic acid as the mordant.

Friedrich Neelsen kept Ziehl's choice of mordant but changed the primary stain to carbol fuchsin.

[citation needed] The mechanism of action of the Ziehl-Neelsen stain is not completely understood, but it is thought to involve a chemical reaction between the acidic dyes and the cell walls of the bacteria.