Pathogens (Fritz Lecture 2 - C. neoformans) Flashcards
What is cryptococcus neoformans?
Globally distributed fungus most commonly associated with soil, bird guano (excrement of sea birgs) and trees
When incubated on culture media, what do C. neoformans form and what is the associated colour change?
- Formation of a polysaccharide capsule
- Colonies turn from brown to black
What are the 2 main species of cryptococcus?
1) C. neoformans, serotypes depending on fine-structure of the capsule
2) C. gattii found predominately in Australia, West Canada and West US
Who is mainly at risk from disseminated cryptococcosis from C. neoformans?
Immunocompromised individuals
- AIDS, steroids, organ transplants
Who is mainly at risk from disseminated cryptococcosis from C. gattii?
Non immunocompromised individuals
Is C.neoformans commensal?
Not generally considered to be a routine constituent of the human microbial biota
What are the 2 main sites of C. neoformans infection?
Lungs and CNS
What are the symptoms of cryptococcosis of the CNS?
Headache Fever Lethargy Coma Memory loss
What is the mortality rate of cryptococcosis of the CNS within the first 2 weeks if not treated?
100%
What is used to treat cryptococcosis?
- Amphotericin B with Flucytosin followed by fluconazole
What is the main virulence factor of C. neoformans?
The polysaccharide capsule
- a-capsular or hypo-capsular mutants are dramatically less virulent
How is C. neoformans diagnosed with high sensitivity?
- Serologic tests of cryptococcal polysaccharide antigen in serum or CSF
- sensitivity: 99%
What is the structure of the C.neroformans polysaccharide capsule?
- Rich in glucuronic acid and mannose
- Unbranched chain of alpha-1-3 linked mannose units substituted with beta-glucuronyl groups
What 3 factors can cause capsule induction?
1) Neutral pH
2) Low iron
3) Elevated carbon dioxide
Describe C.neoformans transmission
- Spores from tress or sea bird excrement inhales into the lungs
- Lodges in the alveoli
- Dissemination to the CNS
