Which staining method is used to visualize encapsulated, budding yeast in cryptococcosis within the CSF?

Which staining method is used to visualize encapsulated, budding yeast in cryptococcosis within the CSF?

• A. Gram stain of CSF
• B. Gram stain of sputum
• C. India ink stain of CSF
• D. Acid-fast stain of CSF

Answer: (C)

The key idea is visualization of the cryptococcal capsule. Cryptococcus neoformans has a large, polysaccharide capsule that doesn’t take up India ink. When CSF is stained with India ink, the ink surrounding the yeast doesn’t enter the capsule, creating a clear halo around budding yeast cells. This halo-dense appearance under the microscope is characteristic of encapsulated yeasts in cryptococcal meningitis and makes India ink staining in CSF the classic diagnostic stain. Other stains like Gram stain can miss organisms in CSF or be less reliable, and acid-fast stains target mycobacteria, not Cryptococcus, while Gram stain of sputum isn’t CSF.

The key idea is visualization of the cryptococcal capsule. Cryptococcus neoformans has a large, polysaccharide capsule that doesn’t take up India ink. When CSF is stained with India ink, the ink surrounding the yeast doesn’t enter the capsule, creating a clear halo around budding yeast cells. This halo-dense appearance under the microscope is characteristic of encapsulated yeasts in cryptococcal meningitis and makes India ink staining in CSF the classic diagnostic stain. Other stains like Gram stain can miss organisms in CSF or be less reliable, and acid-fast stains target mycobacteria, not Cryptococcus, while Gram stain of sputum isn’t CSF.