Cryptococcus neoformans: historical curiosity to modern pathogen

Abstract

The importance of the Basidiomycete Cryptococcus neoformans to human health has stimulated its development as an experimental model for both basic physiology and pathogenesis. We briefly review the history of this fascinating and versatile fungus, some notable aspects of its biology that contribute to virulence, and current tools available for its study.

Keywords: Cryptococcus gattii; Cryptococcus neoformans; capsule; cryptococcosis; meningitis; pathogenic fungus; yeast.

Figure 1

Comparison of infectious disease deaths globally (total bar height) and in Africa alone (white lines). Cryptococcosis (red bar) kills over half a million invididuals annually, mainly in Africa. Numbers shown for cryptococcosis are based on Park et al (Park, et al., 2009). Other values are from World Health Organization regional mortality data for 2002 (WHO, 2002); this year was chosen to best match the cohort study data used in (Park, et al., 2009).

Figure 2

Confocal micrograph of human peripheral blood monocytes (cytosol stained red) with engulfed Cryptococcus (cell walls stained green).

Figure 3

C. neoformans capsule images. Top row: negative stain with India ink; quick freeze deep-etch electron micrograph of a portion of the cell wall with capsule fibers extending to the left); thin section electron micrograph of three cells. Bottom row: immunoelectron micrograph of a portion of a cell (capsule fibers extending upwards) stained with gold-conjugated anticapsule antibody; differential interference contrast micrograph of a budding cell; confocal immunofluorescence micrograph with the capsule stained blue and the cell wall stained green.

Figure 4

Views of C. neoformans. A. Colonies grown on medium containing 0.1% L-DOPA to demonstrate melanization. Top, wild type; bottom, laccase mutant. B. Brightfield microscopy. C. Transmission electron microscopy (pseudocolored). D. Mating filaments.