Negative staining uses which reagent to visualize capsules in Cryptococcus neoformans?

Negative staining uses which reagent to visualize capsules in Cryptococcus neoformans?

• A. India ink or nigrosin stain
• B. Gram stain
• C. Acid-fast stain
• D. Calcofluor white

Answer: (A)

Visualizing the capsule relies on negative staining, where the stain colors the background but not the capsule. Cryptococcus neoformans has a prominent polysaccharide capsule that resists uptake by most stains, so it shows up as a clear halo around the yeast cell. India ink and nigrosin are used because they don’t penetrate the capsule; their dark background creates strong contrast and makes the capsule halo easy to see under the microscope. Other stains—Gram, acid-fast, or Calcofluor white—target the cell wall or internal structures and don’t produce the same halo effect, so they’re not suitable for highlighting the capsule.

Visualizing the capsule relies on negative staining, where the stain colors the background but not the capsule. Cryptococcus neoformans has a prominent polysaccharide capsule that resists uptake by most stains, so it shows up as a clear halo around the yeast cell. India ink and nigrosin are used because they don’t penetrate the capsule; their dark background creates strong contrast and makes the capsule halo easy to see under the microscope. Other stains—Gram, acid-fast, or Calcofluor white—target the cell wall or internal structures and don’t produce the same halo effect, so they’re not suitable for highlighting the capsule.