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Cryptococcus neoformans
Cryptococcus neoformans is an encapsulated basidiomycetous yeast belonging to the class Tremellomycetes and an obligate aerobe that can live in both plants and animals. Its teleomorph is a filamentous fungus, formerly referred to Filobasidiella neoformans. In its yeast state, it is often found in bird excrement. It has remarkable genomic plasticity and genetic variability between its strains, making treatment of the disease it causes difficult. Cryptococcus neoformans causes disease primarily in immunocompromised hosts, such as HIV or cancer patients. In addition it has been shown to cause disease in apparently immunocompetent hosts, especially in developed countries.
Cryptococcus neoformans has undergone numerous nomenclature revisions since its first description in 1895. It formerly contained two varieties: C. neoformans var. neoformans and C. neoformans var. grubii. A third variety, C. neoformans var. gattii, was later defined as a distinct species, Cryptococcus gattii. The most recent classification system divides these varieties into seven species. C. neoformans refers to C. neoformans var. grubii. A new species name, Cryptococcus deneoformans, is used for the former C. neoformans var. neoformans. C. gattii is divided into five species.[citation needed]
The teleomorph was first described in 1975 by K.J. Kwon-Chung, who obtained cultures of Filobasidiella neoformans by crossing strains of the yeast C. neoformans. She was able to observe basidia similar to those of the genus Filobasidium, hence the name Filobasidiella for the new genus. Following changes to the International Code of Nomenclature for algae, fungi, and plants, the practice of giving different names to teleomorph and anamorph forms of the same fungus was discontinued, meaning that Filobasidiella neoformans became a synonym of the earlier name Cryptococcus neoformans.[citation needed]
The genus name Cryptococcus comes from Ancient Greek κρυπτός (kruptós), meaning "hidden", and κόκκος (kókkos), meaning "grain". The specific name neoformans comes from Latin neo-, meaning "new", and fōrmāns, meaning "shaping".
Cryptococcus neoformans typically 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 within the ruins of the Chernobyl Nuclear Power Plant may be able to metabolize ionizing radiation.
Infection with C. neoformans is termed cryptococcosis. Most infections with C. neoformans occur in the lungs, as the fungus enters its host through the respiratory route. Because it is normally a harmless soil fungus, C. neoformans must first adapt to its new environment inside the human body, making several virulent transformations, including the formation of a polysaccharide capsule. The specific factors that enable this transformation involve sensory receptor proteins common to most soil fungi (pH sensors, carbon dioxide sensors, and intracellular iron detectors) which have been adapted to induce C. neoformans cells into rapidly becoming a dangerous, disease-causing organism.
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Cryptococcus neoformans
Cryptococcus neoformans is an encapsulated basidiomycetous yeast belonging to the class Tremellomycetes and an obligate aerobe that can live in both plants and animals. Its teleomorph is a filamentous fungus, formerly referred to Filobasidiella neoformans. In its yeast state, it is often found in bird excrement. It has remarkable genomic plasticity and genetic variability between its strains, making treatment of the disease it causes difficult. Cryptococcus neoformans causes disease primarily in immunocompromised hosts, such as HIV or cancer patients. In addition it has been shown to cause disease in apparently immunocompetent hosts, especially in developed countries.
Cryptococcus neoformans has undergone numerous nomenclature revisions since its first description in 1895. It formerly contained two varieties: C. neoformans var. neoformans and C. neoformans var. grubii. A third variety, C. neoformans var. gattii, was later defined as a distinct species, Cryptococcus gattii. The most recent classification system divides these varieties into seven species. C. neoformans refers to C. neoformans var. grubii. A new species name, Cryptococcus deneoformans, is used for the former C. neoformans var. neoformans. C. gattii is divided into five species.[citation needed]
The teleomorph was first described in 1975 by K.J. Kwon-Chung, who obtained cultures of Filobasidiella neoformans by crossing strains of the yeast C. neoformans. She was able to observe basidia similar to those of the genus Filobasidium, hence the name Filobasidiella for the new genus. Following changes to the International Code of Nomenclature for algae, fungi, and plants, the practice of giving different names to teleomorph and anamorph forms of the same fungus was discontinued, meaning that Filobasidiella neoformans became a synonym of the earlier name Cryptococcus neoformans.[citation needed]
The genus name Cryptococcus comes from Ancient Greek κρυπτός (kruptós), meaning "hidden", and κόκκος (kókkos), meaning "grain". The specific name neoformans comes from Latin neo-, meaning "new", and fōrmāns, meaning "shaping".
Cryptococcus neoformans typically 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 within the ruins of the Chernobyl Nuclear Power Plant may be able to metabolize ionizing radiation.
Infection with C. neoformans is termed cryptococcosis. Most infections with C. neoformans occur in the lungs, as the fungus enters its host through the respiratory route. Because it is normally a harmless soil fungus, C. neoformans must first adapt to its new environment inside the human body, making several virulent transformations, including the formation of a polysaccharide capsule. The specific factors that enable this transformation involve sensory receptor proteins common to most soil fungi (pH sensors, carbon dioxide sensors, and intracellular iron detectors) which have been adapted to induce C. neoformans cells into rapidly becoming a dangerous, disease-causing organism.