Fungal Infections

Species name/ common name

Cryptococcus gattii (Teleomorph Filobasidella bacillispora). Formerly known as Cryptococcus neoformans var. gattii

Subdivided into at least four different molecular types; VGI, VGII, VGIII and VGI. Geographic drivers of molecular types distribution exist.

Natural habitat

Found mostly associated with Red Gum tree, Eucalyptus camaldulensis as well as long list of other many trees (over 50 species), eg. other Eucalyptus spp., Douglas Fir.

Preferred ecological niche decayed hollows and surfaces: longitudinal studies have shown that C. gattii exists in ‘hotspots’ and can transiently or permanently colonise ecological niches. Also recovered from wood products, soil, water, air, various mammals, and other sources.

Geography

Frequency and diversity of molecular types varies by geography. Generally restricted to locations where the lowest winter temperature typically remains above freezing. Found mostly in tropical and subtropical areas: highly endemic in northern Australia, Papua New Guinea and SE Asia such as Malaysia. Also found in British Columbia, Pacific Northwest of USA, South America, Mexico, other part of Asia and infrequently, Europe.

Frequency

42.8 cases adult meningitis/million population in Central Province, Papua New Guinea.

Since 1999, over 218 infections reported from British Columbia and since 2004, over 90 human cases reported in US.

Diseases

Similar to that caused by C. neoformans, but more likely to involve non-immunocompromised patients.

Infection in immunocompetent persons and development of cryptococcomas in lung and brain are far more commonly associated with C. gattii than C. neoformans.

Neurological sequelae rate higher, including blindness, and more difficult to successfully treat. Surgical resection of cryptococcomas often required.

Culture peculiarities

Rapid growth reaching mature colonies in 3 days. Cultures differentiated from C. neoformans and C. grubii by positive (yellow to blue) reaction on canavanine glycine bromothymol blue agar. Cells morphologically indistinguishable from C. neoformans but in addition to round yeast cells, some more oval ones commonly form. Serodiagnostic kites or molecular tests commonly used to confirm this distinction in important cases

Antifungal resistance (intrinsic and acquired)

Generally susceptible to fluconazole, itraconazole, voriconazole and posaconazole but resistant to ketoconazole and miconazole. Azole antifungal MIC values differ among molecular types. Isolates of molecular type VGII have the highest geometric mean (GM) fluconazole MIC values (8.6 μg/mL) compared to isolates of molecular type VGI which have the lowest (1.7 μg/mL). For fluconazole, itraconazole, and voriconazole GM MIC values, VGI < VGIII < VGIV < VGII. GM MIC values for posaconazole similarly represented across molecular types, with the exception that VGII < VGIII and VGIV.

C. gattii has reduced sensitivity to flucytosine. Always resistant to the echinocandins. Optimal susceptibility testing methods not yet developed.

Infections require longer periods of treatment: nearly three-fold longer therapy times are required for patients with C. gattii compared with C. neoformans due to the difficulty in reducing the size of cryptococcomas.

Biosafety level

This organism must be handled in a biosafety level 2 laboratory.

Industrial use

None

Images

C. gattii on the left showing a positive reaction to canavanine glycine bromothymol blue agar, compared to C. neoformans on the right.

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