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 v
The study showed that the capsule did not prevent phagocytosis in vivo, since cells survived and replicated inside macrophages, despite phagolysosomal fusion. In vitro studies were also done to confirm that encapsulated, but not acapsular, yeast cells replicated intracellularly and were toxic to phagocytic cells. With increased incubation times, the number of yeast cells per phagocytic cell increased for the encapsulated, but not the acapsular strain. Mice were infected intratrachealy with serotype D strain of C. neoformans variety neoformans which is capsulated, as well as with an acapsulated strain. The mice were then killed after various time intervals and the lung tissues examined using electron microscopy as well as light microscopy. This gave an accurate localization of yeast cells, and allowed visualization of cellular components.
Some common words found in the essay are:
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Approximate Word count = 1911
Approximate Pages = 8 (250 words per page double spaced)
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