Which staining method uses Chronic and Periodic acid as reagents?

• A. Grocott
• B. Gridley
• C. Gram stain
• D. Ziehl-Neelsen

Answer: (A)

The staining method that uses chromic acid and periodic acid as reagents is the Grocott methenamine silver stain. In this approach, chromic acid oxidizes fungal cell wall polysaccharides to create reactive aldehyde groups, and periodic acid further enhances this oxidation. These activated sites then bind the silver from the methenamine silver solution, producing a dark (often black) stain of the fungal walls with a light counterstain background. This combination of oxidation steps with silver impregnation is characteristic of this fungal stain, making it distinct from Gram or Ziehl-Neelsen methods, which rely on crystal violet/iodine/safranin or carbol fuchsin and acid-alcohol decolorization, respectively.