Fungal Infections

Species name/ common name

  •   Cryptococcosis neoformans (teleomorph Filobasidiella neoformans)
  •   Cryptococcus neoformans  var. neoformans and Cryptococcus neoformans var. grubii.
  •   Cryptococcus gattii used to be regarded as a third variety of C. neoformans. However, based on differences in biochemical, ecological, epidemiological and molecular characteristics, it is now recognized as a separate species
  •   C. neoformans and C. gattii previously classified into five serotypes of C. neoformans: A, B, C, D and AD (hybrids between serotypes A and D) on the basis of antigenic differences between their capsular polysaccharides and using molecular comparison. The two varieties of C. neoformans, var. grubii and var. neoformans, are compromised of serotypes A and D respectively, while C. gattii is comprised of serotypes B and C.

Natural habitat

Isolated most frequently from soil contaminated with pigeon and other bird droppings.

Also isolated from old dried accumulations of bird droppings in buildings, not from fresh wet droppings. The precise link between birds and C. neoformans infection remains unclear as birds are not infected but serve as a vector, spreading the fungus from vegetation throughout the environment. There is no evidence for an association between C. neoformans and specific trees, but two varieties have been isolated from decaying wood of many difference species of trees.

Geography

C. neoformans serotype A accounts for about over 90% of reported human cases, found worldwide. The remaining 5% of infections are caused by C. neoformans serotype D or C. gattii serotypes B and C. Serotype D is found predominantly in European countries.

Frequency

Most common cause of meningitis in hospitals in which persons with HIV infection are treated. Incidence remains high in resource-limited settings such as sub-Saharan Africa and South East Asia.

Diseases

Pulmonary

Central nervous system (meningitis and cryptococcoma)

Cutaneous

Osteomyelitis (especially in patients with sarcoidosis)

Ocular (very rare)

Asymptomatic prostate infection in HIV-negative men

Culture peculiarities

Pasty, smooth to mucoid, cream coloured colonies on Sabouraud dextrose agar. On malt extract agar, mucoid colonies predominate. On chromogenic agar for Candida, brownish gray to light pink colonies. On bird seed agar, colonies are brown.

Mostly spherical budding cells (3-8 mm) with a capsule visible in India ink; rarely absent.

On cornmeal-Tween 80 agar, rounded budding yeast cells present only, without pseudohyphae or hyphae.

Antifungal resistance (intrinsic and acquired)

Generally susceptible to fluconazole, itraconazole, voriconazole and posaconazole but resistant to ketoconazole and miconazole. Always resistant to the echinocandins. Susceptible to amphotericin B with acquired resistance over time, if long term treatment given. Some isolates susceptible to flucytosine. Prophylaxis has potential for development of resistance to fluconazole. Optimal susceptibility testing methods not yet developed.

Biosafety level

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

Industrial use

None

Images

Slope of sputum from an AIDS patients with oral thrush showing Candida albicans and C. neoformans on Sabauroud destrose media (left) (all white colonies) and birdseed agar (right), showing pinpoint dark brown colonies of C. neoformans admixed with the white C. albicans colonies.

Microscopy of C. neoformans found in CSF.

Examples of C. neoformans with markedly different capsule sizes.

Sabouraud agar plate showing Cryptococcus neoformans colonies

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