Which stain is routinely used to visualize fungi in tissue and shows fungal elements with black deposition?

Which stain is routinely used to visualize fungi in tissue and shows fungal elements with black deposition?

• A. Gomori methenamine silver (GMS)
• B. Periodic acid–Schiff (PAS)
• C. Gram stain
• D. India ink

Answer: (A)

Gomori methenamine silver stain is used to visualize fungi in tissue because it specifically deposits silver onto fungal cell walls, creating a dark, nearly black appearance that contrasts strongly with the surrounding tissue. The staining mechanism involves oxidizing fungal polysaccharides with periodic acid to form aldehyde groups, which then reduce silver ions to metallic silver on the fungal walls. This makes hyphae and yeast elements stand out clearly against a lighter background, providing excellent detail for identification in sections. In contrast, periodic acid–Schiff staining highlights fungal walls in magenta, not black, so it doesn’t produce the same dark contrast. Gram stain is not routinely used for tissue fungi and can be variable, while India ink is a negative stain used mainly to reveal encapsulated organisms like Cryptococcus—as a halo around the cell rather than staining the entire fungal structure.

Gomori methenamine silver stain is used to visualize fungi in tissue because it specifically deposits silver onto fungal cell walls, creating a dark, nearly black appearance that contrasts strongly with the surrounding tissue. The staining mechanism involves oxidizing fungal polysaccharides with periodic acid to form aldehyde groups, which then reduce silver ions to metallic silver on the fungal walls. This makes hyphae and yeast elements stand out clearly against a lighter background, providing excellent detail for identification in sections. In contrast, periodic acid–Schiff staining highlights fungal walls in magenta, not black, so it doesn’t produce the same dark contrast. Gram stain is not routinely used for tissue fungi and can be variable, while India ink is a negative stain used mainly to reveal encapsulated organisms like Cryptococcus—as a halo around the cell rather than staining the entire fungal structure.