Chapter: Medical Microbiology: An Introduction to Infectious Diseases: Cryptococcus, Histoplasma, Coccidioides, and Other Systemic Fungal Pathogens

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Cryptococcus neoformans

Cryptococcus neoformans (cryptococcus) is a yeast 4 to 6 m in diameter that produces acharacteristic capsule.

CRYPTOCOCCUS

Cryptococcus neoformans

Cryptococcus neoformans (cryptococcus) is a yeast 4 to 6 m in diameter that produces acharacteristic capsule (Fig 49–1), extending the overall diameter to 25μm or more. This capsule is unique among pathogenic fungi and is a complex polysaccharide polymer, the major component of which is glucuronoxylomannan (GXM). Capsule production varies by strain and with environmental conditions. It is repressed under environmental condi-tions and stimulated in the physiologic conditions found in tissues.

C. neoformans grows at 35 to 37°C on a variety of common media, including bloodagar, chocolate agar, and Sabouraud’s agar. Mucoid, bacteria-like colonies are produced in 2 to 3 days. In addition to the capsule, extracellular products include a urease enzyme and melanin pigment.

The sexual state of C. neoformans places it in the Basidiomycetes, but this form has not been associated directly with disease.

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