Kinyoun's Acid-Fast Stain is used to detect the presence of what in tissue sections?

• A. Acid-fast Mycobacteria
• B. Gram-positive bacteria
• C. Fungi
• D. Nuclei

Answer: (A)

Acid-fast staining targets organisms with waxy cell walls rich in mycolic acids, which resist decolorization by acid-alcohol. Kinyoun's method uses a strong carbol fuchsin dye that penetrates these walls without heating; after applying acid-alcohol, only acid-fast organisms stay red, while the surrounding tissue takes up a contrasting counterstain. In tissue sections, this stain is used to detect acid-fast bacteria, most notably Mycobacterium species such as M. tuberculosis. Other choices—Gram-positive bacteria, fungi, or nuclei—are identified with different staining techniques and do not rely on the acid-fast property.