Cryptococcus neoformans causes meningoencephalitis preferentially in immunocompromised patients. Its polysaccharide capsule is a major virulence factor. Capsular material detected in CSF by India ink preparation reveals:

• A Positively staining polysaccharide in blue-purple color
• B Encapsulated yeast cells staining bright red (positive)
• C Arthroconidia in chains
• D A clear halo (unstained zone) around the yeast cell against a dark background, as India ink particles cannot penetrate the capsule ✓

Explanation

India ink (nigrosin) preparation of CSF demonstrates Cryptococcus capsules as a clear halo around budding yeast cells, because India ink colloidal particles are excluded from the capsular space, leaving a bright unstained zone against a dark background. This is a rapid, low-cost bedside test with ~50–80% sensitivity in AIDS-associated cryptococcal meningitis. Sensitivity is higher in HIV+ patients (who have very high fungal burden) than in other immunocompromised groups. Latex agglutination for cryptococcal antigen (CrAg) is more sensitive.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.