Which reagent is used in the Kinyoun acid-fast staining method?

• A. Acid alcohol
• B. Ethanol
• C. Acetic acid
• D. Methanol

Answer: (A)

Acid-fast staining relies on the cell wall of acid-fast organisms, rich in lipids, to resist decolorization after staining. In the Kinyoun method, a concentrated carbol fuchsin solution with phenol stains the cells without heating. The key step that differentiates acid-fast from non–acid-fast organisms is decolorization with acid-alcohol. Acid-fast cells retain the red stain, while non–acid-fast cells are decolorized and then counterstained for contrast. Among the options, acid alcohol is the reagent used for decolorization in this method. The other reagents listed are not the decolorizer in this procedure.