Microbiology · Yeasts and yeast-like fungi
Cryptococcus neoformans !
- Fungus
- Exam priority: high
A yeast with a thick capsule that lives in soil and bird droppings; inhaled, it can cause meningitis, above all in advanced HIV.
Updated 2026-11-01
Also called: Cryptococcus, Cryptococcus gattii
At a glance
- Shape
- Round, with a narrow-based bud and a capsular halo
- Family
- Cryptococcaceae (Tremellales, basidiomycete)
- Type
- Encapsulated yeast (no hyphae in tissue)
- Stain
- India ink: clear halo around the cell; mucicarmine stains the capsule red; silver (GMS) in tissue
- Size
- Cell of about 4–10 µm without the capsule
Morphology
- Round yeast surrounded by a polysaccharide capsule
- Buds joined to the mother cell by a narrow base
- Makes melanin: brown colonies on birdseed (niger seed) agar
- Urease positive
Transmission
- Inhalation of dried yeasts or spores from soil, decaying wood and bird droppings (C. neoformans)
- C. gattii is linked to trees in tropical and subtropical areas
- Not spread from person to person
Reservoir: Soil and droppings of pigeons and other birds; Tree hollows and decaying wood (mainly C. gattii)
Isolation precautions
What the care team adds to standard precautions.
- Standard
Virulence factors
- Polysaccharide capsule (glucuronoxylomannan): blocks phagocytosis and damps the immune response
- Melanin in the wall: protects against oxidative stress
- Urease: helps it cross the blood-brain barrier
- Grows well at 37 °C and favours the central nervous system
Diseases it causes
- Cryptococcal meningitis: headache over days or weeks, fever, confusion and high intracranial pressure; a major cause of death in advanced HIV Cryptococcal meningitis →
- An opportunistic infection that marks advanced HIV (very low CD4) HIV infection and AIDS →
Clinical picture
- Pneumonia or lung nodules, sometimes without symptoms
- Molluscum-like skin lesions in disseminated disease
- C. gattii can affect immunocompetent people and form masses (cryptococcomas)
Diagnosis
- Cryptococcal antigen (CrAg) in serum or CSF by lateral flow assay: fast and very sensitive
- India ink on CSF: yeasts with a halo; less sensitive than antigen
- CSF or blood culture: the reference standard; tells C. neoformans from C. gattii
- Lumbar puncture with opening pressure (often very high)
Treatment
Meningitis: induction with amphotericin B plus flucytosine, then consolidation and maintenance with fluconazole; fluconazole alone for mild lung disease. High intracranial pressure is managed with repeated lumbar punctures, and antiretrovirals are delayed a few weeks to lower the risk of immune reconstitution syndrome.
Drug class only; doses and regimens are set by the clinician from the current guideline.
In Pharmacology:
Prevention
- Early HIV diagnosis and antiretroviral therapy
- Cryptococcal antigen screening in advanced HIV, with pre-emptive antifungal treatment if positive
- Avoiding exposure to heaps of bird droppings in severely immunosuppressed people
Test yourself
Think of the answer, then tap the question to see it.
Which rapid test in serum or CSF is most useful to diagnose cryptococcosis?
Cryptococcal antigen (CrAg) detection, for example with a lateral flow assay.
What does India ink show in the CSF of a patient with cryptococcal meningitis?
Round yeasts surrounded by a clear halo, which is the capsule.
Which antifungal combination is used in the first phase of cryptococcal meningitis?
Amphotericin B with flucytosine, followed later by fluconazole.
Why are antiretrovirals delayed in cryptococcal meningitis?
To lower the risk of immune reconstitution inflammatory syndrome, which can worsen meningeal inflammation.
Related
Related conditions
← Back to the group: Yeasts and yeast-like fungi
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: About Cryptococcosis (CDC, 2024); Clinical Overview of Cryptococcosis (CDC, 2024); Meningitis - cryptococcal (MedlinePlus (NLM), 2024); Early HIV diagnosis could reduce AIDS-related deaths in Latin America and the Caribbean: PAHO (PAHO/WHO, 2025).
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Representative model, for educational purposes only.