Cryptococcus Neoformans

BackgroundThe organism C neoformans is an encapsulated yeast; its environmental niche has not been completely defined, although outbreaks of disease have been associated in particular with pigeon roosts and other large contaminated sites. There are two varieties of C neoformans, distinguished by antigenic differences in the outer capsule of the organism: serotypes A and D (C neoformans var neoformans, the most common strain) and serotypes B and C (C neoformans var gatti). Cryptococcus neoformans var neoformans is the principal pathogen in patients with AIDS. Cryptococcus neoformans var gatti, which is found predominantly in Australia, Asia, and Southern California, has only rarely been implicated to cause disease in this population.
Antigenic specificity of the capsular polysaccharides define the four different serotypes of C. neoformans; A, B, C and D. C. neoformans variety neoformans includes serotypes A and D while C. neoformans var. gattii are associated with serotypes B and C. Worldwide, most Cryptococcal infections in immunocompromised patients, including HIV infected patients, are due to C. neoformans var. neoformans, serotype A. In a smaller number of immunocompromised patients, infecton is caused by C. neoformans var. neoformans, Serotype D. For unknown reasons, HIV infected patients and other immunosuppressed patients are rarely infected with the variety gattii. Patients infected with C. neoformans var. gattii are usually immunocompetent, respond slowly to treatment, and are at risk for developing intracerebral mass lesions (cryptococcomas).
Cryptococcus neoformans reproduces by budding and forms round yeast-like cells 3-6 micrometers in diameter. Within the host and in certain culture media, a large polysaccharide capsule surrounds each cell. Cryptococcus neoformans forms smooth, convex, yellow or tan colonies on solid media at 20 to 37 degrees Celsius. The identification of this fungus is based on its microscopic ap…

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