Cryptococcus

Overview
Cryptococcus (literally "Hidden Seed") is a genus of fungus. It grows in culture as a yeast. The perfect (sexual) form or teleomorph is called Filobasidiella, but the imperfect (asexual) form or anamorph is called Cryptococcus. The name Cryptococcus is correct when used in a medical context because the infective form is the imperfect form.

Cryptococcus neoformans is the most prominent medically important species. It is best known for causing a severe form of meningitis and meningo-encephalitis in persons with HIV infection and AIDS. There are about 37 recognized species of Cryptococcus, but the taxonomy of the group is currently being re-evaluated with up-to-date methods. The majority of species live in the soil and are not harmful to humans. Very common species include Cryptococcus laurentii and Cryptococcus albidus. Of all species, Cryptococcus neoformans is the major human and animal pathogen. However, Cryptococcus laurentii and Cryptococcus albidus have been known to occasionally cause moderate-to-severe disease in human patients with compromised immunity (owing to HIV infection, cancer chemotherapy, metabolic immunosuppression, et cetera) [Reference 1, 2].

Cryptococcus gattii (or Cryptococcus neoformans var gattii) is endemic to tropical parts of the continent of Africa and Australia. It is capable of causing disease in non-immunocompromised people. It is has been isolated from eucalyptus trees in Australia. Since 1999, there has been an outbreak of cryptococcus gattii infections in eastern Vancouver Island, an area not generally thought to be endemic for this organism. Cases have since been described in the Pacific northwestern United States.

The cells of these species are covered in a thin layer of glycoprotein capsular material that has a gelatin-like consistency and that, among other functions, serves to help extract nutrients from the soil. But C. neoformans capsule is different in being richer in glucuronic acid and mannose, having O-acetyl groups [Reference 3], and functioning as the major virulence factor in cryptococcal infection and disease [Reviewed extensively in Reference 4].

References:

1. Cheng MF, Chiou CC, Liu YC, Wang HZ, Hsieh KS (2001) Cryptococcus laurentii fungemia in a premature neonate. Journal of Clinical Microbiology. 39(4):1608-11. - a good review of C. laurentii cases till year 2000.

2. Results from a PubMed Search on terms: "Cryptococcus albidus Infection" - list of references for C. albidus clinical infections. Click on the hyperlink to go to the PubMed Search page.

3. Ross A, Taylor IE (1981) Extracellular glycoprotein from virulent and avirulent Cryptococcus species. Infection and Immunity. 31(3):911-8

4. Casadevall A and Perfect JR (1998) Cryptococcus neoformans. American Society for Microbiolgy, ASM Press, Washington DC, 1st edition.