page_title: Cryptococcus neoformans
section_title: Characteristics
hierarchical_section_title: Cryptococcus neoformans / Characteristics
caption_attribution_description: English: Cryptococcus neoformans, an encapsulated yeast, stained by Gram's method. Preparation by Tina Demers.
context_page_description: Cryptococcus neoformans is an encapsulated yeast and an obligate aerobe that can live in both plants and animals. Its teleomorph is Filobasidiella neoformans, a filamentous fungus belonging to the class Tremellomycetes. It is often found in bird excrement. Cryptococcus neoformans is an encapsulated fungal organism and it can cause disease in apparently immunocompetent, as well as immunocompromised, hosts.
context_section_description: C. neoformans grows as a yeast (unicellular) and replicates by budding. It makes hyphae during mating, and eventually creates basidiospores at the end of the hyphae before producing spores. Under host-relevant conditions, including low glucose, serum, 5% carbon dioxide, and low iron, among others, the cells produce a characteristic polysaccharide capsule. The recognition of C. neoformans in Gram-stained smears of purulent exudates may be hampered by the presence of the large gelatinous capsule which apparently prevents definitive staining of the yeast-like cells. In such stained preparations, it may appear either as round cells with Gram-positive granular inclusions impressed upon a pale lavender cytoplasmic background or as Gram-negative lipoid bodies.
  When grown as a yeast, C. neoformans has a prominent capsule composed mostly of polysaccharides. Under the microscope, the India ink stain is used for easy visualization of the capsule in cerebral spinal fluid. The particles of ink pigment do not enter the capsule that surrounds the spherical yeast cell, resulting in a zone of clearance or "halo" around the cells. This allows for quick and easy identification of C. neoformans. Unusual morphological forms are rarely seen. For identification in tissue, mucicarmine stain provides specific staining of polysaccharide cell wall in C. neoformans. Cryptococcal antigen from cerebrospinal fluid is thought to be the best test for diagnosis of cryptococcal meningitis in terms of sensitivity, though it might be unreliable in HIV-positive patients.
  The first genome sequence for a strain of C. neoformans (var. neoformans; now C. deneoformans) was published in 2005.
  Studies suggest that colonies of C. neoformans and related fungi growing on the ruins of the melted down reactor of the Chernobyl nuclear power plant may be able to use the energy of radiation for "radiotrophic" growth.
caption: C. neoformans stained by Gram stain
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