Which acid-fast staining method requires heating?

Which acid-fast staining method requires heating?

• A. Kinyoun
• B. Ziehl-Neelsen
• C. Dieterle
• D. Wright's

Answer: (B)

The key idea is that mycobacteria have a waxy, lipid-rich cell wall that resists staining, so some acid-fast methods use heat to force dye into the wall. In the Ziehl-Neelsen procedure, gentle heating with carbol fuchsin helps the stain penetrate the cell wall, and after decolorization with acid-alcohol, acid-fast organisms retain the red stain while non–acid-fast organisms do not. The other approaches achieve similar staining without heat: the Kinyoun method uses a higher concentration of phenol to soften the wall and allow dye entry at room temperature, so heating isn’t required. Dieterle and Wright’s methods are different stain techniques and aren’t the heat-dependent acid-fast approach. Therefore, heating is a defining feature of the Ziehl-Neelsen acid-fast stain.

The key idea is that mycobacteria have a waxy, lipid-rich cell wall that resists staining, so some acid-fast methods use heat to force dye into the wall. In the Ziehl-Neelsen procedure, gentle heating with carbol fuchsin helps the stain penetrate the cell wall, and after decolorization with acid-alcohol, acid-fast organisms retain the red stain while non–acid-fast organisms do not.

The other approaches achieve similar staining without heat: the Kinyoun method uses a higher concentration of phenol to soften the wall and allow dye entry at room temperature, so heating isn’t required. Dieterle and Wright’s methods are different stain techniques and aren’t the heat-dependent acid-fast approach. Therefore, heating is a defining feature of the Ziehl-Neelsen acid-fast stain.