DESCRIPTIONS OF MEDICAL FUNGI

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Descriptions of Medical Fungi
Cryptococcus gattii (Vanbreus. & Takashio) Kwon-Chung & Boekhout
Synonymy: Filobasidiella bacillispora Kwon-Chung.
Cryptococcus neoformans var. gattii Vanbreus. & Takashio.
RG-2 organism.
Cryptococcus gattii has two serotypes (B and C) and was reclassified as a separate
species from C. neoformans in 2002 (Kwon-Chung et al. 2002). C. gattii generally has a
more restricted geographical distribution than C. neoformans, causing human disease
in climates ranging from temperate to tropical Australia, Papua New Guinea, parts of
Africa, India, Southeast Asia, Mexico, Brazil, Paraguay and Southern California, although
recent infections have also been reported from Vancouver Island, Canada and in the
Pacific Northwest, USA (Pfaller & Diekema, 2010, Espinel-Ingroff and Kidd, 2015). C.
gattii has a specific ecological association with numerous species of Eucalyptus trees,
although the Canadian isolates are associated with a range of native non-Eucalyptus
species (Kidd et al. 2007). Historically considered a pathogen in immunocompetent
hosts, a recent review in Australia noted an increase in C. gattii infections in HIVnegative
immunocompromised patients (Chen et al. 2012). Cryptococcosis caused by
C. gattii is often associated with large mass lesions (cryptococcomas) in the lung and/
or brain (Sorrell, 2001).
Canavanine glycine bromothymol blue (CGB) agar (Kwon-Chung et al. 1982) is the
media of choice to differentiate C. gattii from C. neoformans. This simple biotype test is
based on the ability of C. gattii isolates to grow in the presence of L-canavanine and to
assimilate glycine as a sole carbon source. A heavy inoculum is important.
Cryptococcus gattii turns CGB agar blue within 2-5 days;
Cryptococcus neoformans does not grow on this medium