To differentiate Cryptococcus neoformans from other yeast-like fungi, which stain should be performed?

• A. Mayer mucicarmine
• B. India ink
• C. Gram stain
• D. PAS stain

Answer: (A)

The distinguishing feature here is the capsule of Cryptococcus neoformans. This organism has a prominent polysaccharide capsule that can be highlighted specifically with Mayer mucicarmine, which binds the acidic capsule material and stains it a distinct red/pink. Seeing a clearly stained capsule around the yeast on a tissue or smear strongly supports cryptococcosis and helps separate Cryptococcus from other yeast-like fungi that lack this capsule or don’t take up the dye in the same way.

India ink can reveal a capsule as a negative halo in unstained CSF samples, but it’s less specific and reliable, especially in fixed specimens or routine slides. Gram stain shows general yeast morphology but does not differentiate based on capsule. PAS stain highlights fungal cell walls broadly, not specifically the cryptococcal capsule, so it isn’t as helpful for differentiation.