DESCRIPTIONS OF MEDICAL FUNGI

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Descriptions of Medical Fungi
Cryptococcus Kützing emend. Phaff & Spencer
The genus Cryptococcus is characterised by globose to elongate yeast-like cells or
blastoconidia that reproduce by narrow-necked budding. Pseudohyphae are absent or
rudimentary. Most species are encapsulated, although the extent of capsule formation
depends on the medium. Under certain conditions of growth, the capsule may contain
starch-like compounds, which are released into the medium by many strains. Within
tissue sections, mucicarmine or Alcian blue stains the capsule of Cryptococcus species
to distinguish it from other yeasts with similar morphologies.
On solid media the cultures are generally mucoid or slimy in appearance; red, orange or
yellow carotenoid pigments may be produced, but young colonies of most species are
usually non-pigmented, and cream in colour. All Cryptococcus species produce urease
and are non-fermentative. Nitrate may be assimilated or not; inositol assimilated. The
genus Cryptococcus differs from the genus Rhodotorula in its inositol assimilation.
Cryptococcosis is a chronic, subacute to acute pulmonary, systemic or meningitic
disease, initiated by the inhalation of infectious propagules (basidiospores and/or
desiccated yeast cells) from the environment. Primary pulmonary infections have no
diagnostic symptoms and are usually subclinical. On dissemination, the fungus usually
shows a predilection for the central nervous system, however skin, bones and other
visceral organs may also become involved. Although C. neoformans and C. gattii are
regarded as the principle pathogenic species, Cryptococcus albidus and C. laurentii
have on occasion also been implicated in human infection.
Molecular Identification: Requires ITS and/or D1/D2 sequencing, particularly for
identification of unusual species.
MALDI-TOF MS: Can provide reliable species and subspecies level identification of
Cryptococcus species, but its accuracy is dependent on database quality (Arendrup et
al. 2014).
a
b
5 μm
Cryptococcus neoformans (a) culture appearances on bird seed agar (brown colonies)
and Candida albicans (white colonies) and (b) India Ink preparation of C. neoformans
surrounded by a characteristic wide gelatinous capsule.
References: Rippon (1982), Barnett et al. (1983), Kurtzman et al. (2011), Casadevall
and Perfect (1998), de Hoog et al. (2000, 2015), McTaggart et al. (2013).