Mycobacteria can be examined by using which stain?

• A. Dieterle stain
• B. Gimenez stain
• C. Kinyoun stain
• D. Wright's stain

Answer: (C)

Mycobacteria have a lipid-rich cell wall with mycolic acids, which makes them resistant to decolorization by acid alcohol. This trait is why acid-fast staining is used to visualize them. The Kinyoun stain is a cold (non-heat) acid-fast method that uses a high concentration of carbol fuchsin with phenol to penetrate the waxy cell wall. After applying acid-alcohol as a decolorizer, acid-fast organisms retain the red color of the primary stain while non–acid-fast cells take up a counterstain. This yields bright red Mycobacterium against a contrasting background, making it a preferred stain for detecting these bacteria in clinical specimens.

The other stains listed are not used for acid-fast visualization of mycobacteria: Wright's stain is a Romanowsky-type stain used for blood cell morphology; Gimenez stain is a method for certain intracellular bacteria and parasites in tissues; Dieterle stain is a silver-based stain used for various organisms in tissues, not specifically for acid-fast organisms like Mycobacteria.