Which stain is used to visualize fungal capsules in Cryptococcus using a pink capsule?

Which stain is used to visualize fungal capsules in Cryptococcus using a pink capsule?

• A. Giemsa stain
• B. India ink
• C. Mucicarmine stain
• D. Gram stain

Answer: (C)

Staining strategies to reveal the cryptococcal capsule rely on dyes that bind the polysaccharide capsule, making the capsule visible around the yeast cell. Cryptococcus has a prominent polysaccharide capsule, so using a stain that specifically binds this material will color the capsule. Mucicarmine is such a stain; it binds acidic mucopolysaccharides in the capsule and stains it pink, producing a characteristic pink halo that distinguishes Cryptococcus from other yeasts. India ink, by contrast, shows the capsule as a clear halo because it is a negative stain and does not color the capsule itself. Giemsa and Gram stains are not designed to highlight the capsule and thus don’t reveal it clearly. Therefore, mucicarmine staining is the best choice to visualize the pink capsule.

Staining strategies to reveal the cryptococcal capsule rely on dyes that bind the polysaccharide capsule, making the capsule visible around the yeast cell. Cryptococcus has a prominent polysaccharide capsule, so using a stain that specifically binds this material will color the capsule. Mucicarmine is such a stain; it binds acidic mucopolysaccharides in the capsule and stains it pink, producing a characteristic pink halo that distinguishes Cryptococcus from other yeasts. India ink, by contrast, shows the capsule as a clear halo because it is a negative stain and does not color the capsule itself. Giemsa and Gram stains are not designed to highlight the capsule and thus don’t reveal it clearly. Therefore, mucicarmine staining is the best choice to visualize the pink capsule.