Cryptococcus neoformans

University of Oklahoma Study Abroad Microbiology in Arezzo, Italy[1]

File:Cdiphtheriametachromatic.jpg

C. diphtheriae bacteria, in green, showing metachromatic granules on the ends of the cell. From: http://textbookofbacteriology.net/diphtheria.html

Classification

Higher order taxa

Eukaryota (Kingdom); Fungi (Domain); Basidiomycota (Phylum); Tremellomycetes (Class); Tremellales (Order); Tremellaceae (Family); Cryptococcus (Genus)

NCBI: Taxonomy Genome: Cryptotoccus neoformans

Species

C. neoformans v. neoformans, C. neoformans v. grubii. A third variety, C. neoformans v. gattii, is now considered a distinct species, Cryptococcus gattii.

Description

Cryptococcus neoformans is an encapsulated fungal pathogen causing fatal meningitis in humans. The infection, initiated by inhalation into the lungs, occurs mainly in immunocompromised individuals, but can also occur in healthy individuals. Cryptococcus neoformans is usually found in tissues in the yeast form. Infection of the brain and meninges is the most common clinical manifestation. In immunocompetent individuals, the initial infection is usually controlled and asymptomatic and the organism remains dormant in a lymph node complex, much like tuberculosis. Reactivation occurs in immunocompromised hosts where the fungus can spread via the blood to infect the central nervous system. Once C. neoformans reaches this stage it can cause meningitis that is uniformly fatal if untreated. Few antifungal agents exist and drug-resistant strains are emerging.

Genome structure

Most isolates of C. neoformans are haploid. The size of the genome is approximately 19 Mb with 14 chromosomes. Cryptococcus neoformans has a defined sexual cycle involving mating between cells of the MATalpha and MATa types. Thus, classical genetic approaches can be applied to study this organism.

Pathology

Cryptococcus neoformans is an opportunistic fungal pathogen that may cause meningitis in immunocompromised individuals. Often found in soils contaminated with bird feces, C. neoformans enters its host through the lungs via inhalation of spores. In healthy individuals the infection is usually controlled and asymptomatic, but in immunocompromised hosts the fungus can spread via the blood to infect the central nervous system and cause meningitis that is uniformly fatal if untreated. Few antifungal agents exist and drug-resistant strains are emerging.