Kinyoun

Kinyoun stain, also known as the cold acid-fast stain, is a microbiological technique used to detect acid-fast bacteria in clinical specimens. It was developed by Joseph J. Kinyoun in the late 19th to early 20th century as a modification of the Ziehl-Neelsen method, allowing acid-fast staining without the need for heating. The method relies on a highly phenolized, lipid-soluble primary stain, carbol fuchsin, which penetrates the waxy cell walls of acid-fast organisms such as Mycobacterium and Nocardia. After staining, non–acid-fast cells are decolorized with a milder acid-alcohol, and the acid-fast organisms retain the red color and are counterstained with a contrasting dye, typically methylene blue, producing red rods against a blue background.

The procedure is performed on smear slides or tissue sections, often from sputum or biopsies. The stain is valued for its simplicity and safety in settings where heating equipment is limited, since it does not require heat to drive dye penetration. It is particularly useful for rapidly screening for mycobacterial infections, though some organisms may yield stronger signals with alternative methods. Compared with the fluorescent acid-fast stains, the Kinyoun method may be less sensitive for certain pathogens but remains widely used in many laboratories, especially in resource-limited environments.

Limitations include the potential for variability in staining and interpretation, dependence on specimen quality, and occasionally lower sensitivity for certain bacteria. Proper handling of phenol-containing reagents is required. Related methods include the Ziehl-Neelsen stain and fluorescent acid-fast stains such as the auramine-rhodamine technique.