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.