Cryptococcosis, emphasis on C' neoformans

1
Cryptococcosis, emphasis on C. neoformans

• Identification
• Cryptococcus species are encapsulated yeast in
  the fungal phylum Basidiomycota only
  Basidiomycete of medical importance.
• They form yeast mono-layers on CMT-80 that do not
  touch each other (?) because capsule keeps them
  apart
• Cryptococcus species are urease positive
• C. neoformans is the only yeast to produce phenol
  oxidase (dark colonies on bird seed agar or other
  substrates) POX produces melanin which protects
  environmental organisms from oxidative damage

2
Cryptococcosis, Emphasis on C. neoformans

• Etiology Virtually all cases of cryptococcosis
  are cause by C. neoformans
• Epidemiology
• Cryptococcus neoformans is not part of the human
  indigenous microbiota
• It is found world-wide in soil enriched by bird
  droppings (in particular pigeon poop), and
  rotting eucalyptus wood (for whatever that is
  worth).

3
Cryptococcosis, Emphasis on C. neoformans

• Epidemiology
• Bird droppings are rich in urea which might
  explain why the organism has the enzyme urease
  and why it also uses substrates in bird seed agar

4
Cryptococcosis, Emphasis on C. neoformans

• Epidemiology
• Cryptococcosis is prevalent in and around old
  buildings on which pigeons have made their home
  (e.g. VES and VHB to name just two)
• Cryptococcosis is acquired by inhalation of
  airborne conidia
• Immunocompetent and uncompromized healthy
  individuals usually are asymptomatic

5
Cryptococcosis, Emphasis on C. neoformans

• Epidemiology
• People with AIDS, carcinoma, leukemia, and
  Hodgkins lymphoma (among others) are at high
  risk of developing serious life-threatening
  disease, although AIDS is the primary
  predisposing factor.

6
Cryptococcosis, Emphasis on C. neoformans

• Clinical manifestation
• The disease begins in the lung
• It can be asymptomatic or mild and self limiting
  in healthy individuals
• In the immunocompromized host it can cause severe
  pulmonary disease
• It can also disseminate to the central nervous
  system (meningoencephalitis 1 clinical
  pathology), internal organs, bones, skin and
  mucous membranes

7
Cryptococcosis, emphasis on C. neoformans

• Laboratory Identification
• Cryptococcus species are the only yeast to
  assimilate inositol, a unique carbohydrate
• Cryptococcus produces capsules (India Ink can be
  used to demonstrate capsules in clinical
  specimens but the ability for Cryptococcus to
  produce a capsule in vitro is sometimes lost)
• Cryptococcus produces only encapsulated budding
  yeast on CMT 80

8
Cryptococcosis, emphasis on C. neoformans

• Laboratory Identification
• The first clue an isolate might be a Cryptococcus
  species is that is grows well at 37oC and is
  mucoid
• Mucoid colonies usually indicate the yeast is
  producing large capsules, a characteristic of
  only Cryptococcus and Rhodotorula species
• Capsules from young cultures can be demonstrated
  in wet preps mixed with India ink

9
Cryptococcus Gross and Microscopic
C. neoformans on Bird Seed Agar