Which organism is encapsulated and best visualized as a capsule halo with India ink in CSF?

Which organism is encapsulated and best visualized as a capsule halo with India ink in CSF?

• A. Cryptococcus neoformans
• B. Candida albicans
• C. Aspergillus fumigatus
• D. Histoplasma capsulatum

Answer: (A)

The capsule halo seen around a yeast in India ink staining of CSF points to Cryptococcus neoformans. India ink works by not staining the capsule, so the capsule resists ink and remains as a clear halo around the cell against a dark background. This thick polysaccharide capsule is a defining feature of Cryptococcus and is responsible for its virulence, often visualized in CSF with India ink and further highlighted by mucicarmine staining or by antigen tests in suspected cryptococcal meningitis. Candida albicans does not form a true capsule and shows budding yeast with pseudohyphae rather than a halo; Aspergillus fumigatus presents hyphae rather than encapsulated yeast; Histoplasma capsulatum is a small intracellular yeast without a capsule.

The capsule halo seen around a yeast in India ink staining of CSF points to Cryptococcus neoformans. India ink works by not staining the capsule, so the capsule resists ink and remains as a clear halo around the cell against a dark background. This thick polysaccharide capsule is a defining feature of Cryptococcus and is responsible for its virulence, often visualized in CSF with India ink and further highlighted by mucicarmine staining or by antigen tests in suspected cryptococcal meningitis. Candida albicans does not form a true capsule and shows budding yeast with pseudohyphae rather than a halo; Aspergillus fumigatus presents hyphae rather than encapsulated yeast; Histoplasma capsulatum is a small intracellular yeast without a capsule.