Monday 6 September 2010

Cryptococcus neoformans

Cryptococcus neoformans

Worldwide distribution often found in soil contaminated with bird excrement, in particular, pigeon droppings have frequently been implicated.

Cryptococcus neoformans is a rapidly growing typically round yeast (5-10µm) capable of producing polysaccharide capsules which often surround the cell. A 1% peptone solution might aid encourage capsule production. Some species &/or strains of Cryptococcus will not produce capsules in-vitro. Capsule production is best demonstrated using the India-ink (or Nigrosen) negative staining technique. Colonies producing capsules on culture are often evident by their glistening wet or mucoid appearance whereas colonies which fail to produce capsules or have diminished ability to form capsules typically produce dull, creamy, butyrous colonies. Cryptococcus neoformans can be sub-typed further based on serological response to capsular antigens.

Click on Photo to Enlarge
Urease Test Positive: (urea split to release ammonia which raises the pH of the phenol red indicator in the media turning it from a straw colour to a bright pink.)
C.neoformans and other Cryptococci inhibited by Cycloheximide.
C.neoformans can be differentiated from other Cryptococcus species using the Caffeic acid test (a substance used as a substrate to demonstrate phenoloxidase activity. If phenoloxidase is present, it breaks down caffeic acid to melanin with resulting brown-black colour production.) Note: phenoloxidase is inhibited by the presence of glucose so culture the yeast on a glucose-free media such as Cornmeal-Tween 80 agar.
C.neoformans grows well at 25oC as well as 37oC. Some other Cryptococcus species will not grow at 37oC.
Cryptococcus neoformans & most other Cryptococcus species do not produce pseudohyphae.

Clinical Manifistations;
Cryptococcus infections can be found with increasing frequency amongst HIV patients and others who are immunocomprimised however Johns Hopkins Medical center has noted an interesting pattern regarding the serotypes of C.neoformans.
C.neoformans v. neoformans is the most common, usually afflicting immunocompromised hosts while C.neoformans v. gattii is most common in immunocompetent hosts.

Cryptococcus neoformans infection is primarily acquired through inhalation and may invade;
  • Respiratory system - (Sputum, Broncheal Wash, Lung Biopsy)
  • Central Nervous System (CNS) - (Lumbar Puncture)

Also implicated in;
  • Skin infections
  • Bone infections
  • Other sites (disseminated)

Treatment; (dependent on site of infection)
Amphotericin B

Prognosis varies.

The photos on this post were taken from speimens obtained from an 80 year old woman of Indian heritage who presented with respiratory distress. Unfortunately she succumbed to her infection.

Gram stain of sputum specimen 1000X showing cell & size variations
(Inset: Top -Cell showing Capsule, Bottom -Budding cell and clear capsule)

India Ink preparation taken from SAB isolate showing numerous Cryptococcal cells surrounded by clear capsule (negative staining)
(Inset: Enlarged photo of Cryptococcal cell & budding daughter cell surrounded by clear capsule)

Rather unremarkable round Cryptococcal cells taken from Cornmeal Agar Plate

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