Cryptococcus Flashcards
1
Q
1) classification
A
Kingdom: fungi
Family: tremellaceae
Genus: cryptococcus
Species: neoformans
2
Q
2) morphology
A
- spherical budding yeast cells
- surrounded by thick non staining capsule
3
Q
3) growth characteristics
A
- obligate aerobes
- urease positive
- laccase (a phenol oxidase) that catalyses formation of melanin from phenolic substrates (e.g. catecholamines)
This is specific for C. Gattii and C.neoformans and distinguishes then from nonpathogenic species
4
Q
4) Antigenic structure
A
Capsular polysaccharide
5
Q
5) virulence factors
A
- capsule
- melanin pigment formation
- urease activity
6
Q
6) disease
A
- meningitis
- skin and lung infection
7
Q
7) microbiological diagnosis
A
DME:
India ink preparation:
- direct from CSF
- yeast cell, surrounded by wide unstained capsule
Cultures:
Sabouraud’s agar: cream coloured shiny and mucoid colonies
Specific test:
- brown pigment on specific medium
- urease production
- immunofluorescence assay
Direct antigen test:
- Latex agglutination tests detects polysaccharide capsular antigen in spinal fluid
8
Q
8) treatment and prevention
A
Amphotericin B and fluconazole
