ZiehlNeelseni

The Ziehl-Neelsen stain, often abbreviated as ZN stain, is a differential staining technique used in microbiology and histology. It is particularly effective for identifying acid-fast bacilli (AFB), a group of bacteria characterized by their waxy cell walls, most notably Mycobacterium tuberculosis, the causative agent of tuberculosis.

The procedure involves staining a specimen with a concentrated carbolfuchsin dye solution, which is then heated to facilitate penetration into the waxy cell wall. Following this, an acid-alcohol solution is used as a decolorizer. The key feature of acid-fast organisms is their resistance to decolorization by this acid-alcohol mixture, meaning they retain the carbolfuchsin dye and appear red. Non-acid-fast bacteria and other cellular material are decolorized by the acid-alcohol. Finally, a counterstain, typically methylene blue or malachite green, is applied to color the decolorized cells and background, making the red, acid-fast bacilli easily visible under a microscope.

The Ziehl-Neelsen stain is a crucial diagnostic tool, especially in resource-limited settings, for the rapid identification of tuberculosis and other mycobacterial infections. While newer molecular methods exist, the ZN stain remains a cost-effective and widely used technique for initial screening and diagnosis. Its reliability and simplicity have made it a cornerstone of diagnostic microbiology for over a century.