Which organism's capsule is highlighted by Mayer mucicarmine staining?

• A. Cryptococcus neoformans
• B. Staphylococcus aureus
• C. Escherichia coli
• D. Pseudomonas aeruginosa

Answer: (A)

Mayer mucicarmine binds acidic mucopolysaccharides, so it highlights capsules that are rich in polysaccharides. Cryptococcus neoformans has a prominent polysaccharide capsule, and when stained with mucicarmine, the capsule takes up the dye and appears magenta around the yeast cell. This makes the capsule a conspicuous pink/red halo, which is a characteristic way to identify Cryptococcus in tissue preparations. The other organisms listed may have capsules, but their capsules do not stain in the same magenta way with this dye, so they wouldn’t be highlighted by Mayer mucicarmine in the same manner.