In contrast, GXM and GalXM make up the bulk of the capsule (>90% by weight) and have immunosuppressive effects 11. While MPs are a relatively minor cell wall-associated component of the capsule, they are immunogenic and can promote a mostly pro-inflammatory response 9, 10. The cryptococcal capsule is made of up three principle components: glucuronoxylomannan (GXM), galactoxylomannan (GalXM), and mannoproteins (MPs) 9. The polysaccharide capsule is considered the microbe's primary virulence factor, as acapsular strains are not virulent 8. Upon entering the lungs, there are several virulence factors that contribute to the success of C. The most common route of exposure occurs from inhaling desiccated spores that are commonplace in the environment 7. neoformans kills more people than tuberculosis annually and more every month than any Ebola outbreak on record 1. Data from the CDC indicate that in sub-Saharan Africa, C. Hardest hit are HIV-positive patients in poor countries who do not have ready access to antiretroviral therapy, making them acutely susceptible to the illness 4, 5, 6. Finally, we show how measurement of capsule diameter from India ink-stained samples can be automated using computational image analysis.Īffecting a quarter million people every year and resulting in more than 180,000 deaths annually, Cryptococcus neoformans is a pathogenic, intracellular yeast and the causative agent of cryptococcosis 1, 2, 3. Here we describe one of the standard methods of capsule induction and compare two accepted methods of staining and measuring capsule diameter: (i) India ink, a negative stain, used in conjunction with conventional light microscopy and (ii) co-staining with fluorescent dyes of both the cell wall and capsule followed by confocal microscopy. neoformans capsule is induced during phenotypic testing to help understand the effects of different treatments on the yeast or size differences between strains. For these reasons, the size of the capsule is of great interest to C. Capsule size can vary widely between strains, has the ability to grow rapidly when introduced to stressful or low nutrient conditions, and has been positively correlated with strain virulence. The polysaccharide capsule of Cryptococcus neoformans is the primary virulence factor and one of the most commonly studied aspects of this pathogenic yeast.
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