Australian Society of CytologyCase of the Month
April 2004 - Answer and Discussion
Answer: Cryptococcus Neoformans.
Discussion:
Cryptococcus is an encapsulated yeast which may show some budding but no true hyphae. The single bud is attached by a narrow isthmus. Non encapsulated forms do occur, particularly in AIDS patients. There are around 37 species and among these, cryptococcus neoformans is the only species that is pathogenic. Colonies of cryptococcus neoformans grow in a temperature of 37C and usually take 48-72 hours.
The mucoid capsule stains pale and translucent with Pap or MGG stain but a diagnostic bright magenta with Mayer’s mucicarmine. Is it PAS +ve and the capsule also stains with Alcian Blue however Indian Ink preparations demonstrate this best.
Cryptococcus was first identified in nature from peach juice however since then it is most commonly found in soil, especially that which has been contaminated with pigeon droppings. (cryptococcus neoformans var. neoformans).It is also found in eucalyptus trees and decaying wood forming hollows in living trees ( cryptococcus neoformans var.gatti)
The two varieties, neoformans and gatti are morphologically similar. The basidiospores of var. neoformans are round and those of gatti are more elliptical in shape.
Cryptococcus neoformans is the causative agent of cryptococcosis, the most common clinical form being meningoencephalitis. It may also involve the skin, lungs, prostate gland, urinary tract, eyes, myocardium, bones and joints. The infection may be acute or chronic and occur in both immunocompetent and immonocompromised patients. Most susceptible are patients with T cell deficiencies and it is most common in the USA and Australia.
It is generally accepted that the organism enters the host by the respiratory route in the form of a dehydrated haploid yeast or as basidiospores. Once inside the lungs, the yeast cells become rehydrated and aquire the characteristic polysaccaride capsule. In the case of basidiospores, they would convert to encapsulated blastoconidia. After some time in the lungs, the organism hematogenously spreads to extrapulmonary tissues especially the brain where the infected person contracts meningioencephalitis which if left untreated is 100% fatal. There may be an inflammatory response.
In this particular case it is thought the patient inhaled some potting mixture. No symptoms presented for some time and by the time they did, the disease was systemic. Sadly, the patient died.
References:
Diagnostic Cytopathology . Winifred Gray. p 548, 906-7.
Kent L et al.1998 .What makes Cryptococcus neoformans a pathogen?.
University of Oklahoma Health Sciences Center. Oklahoma USA.
“Doctor Fungus” on the www, including:
- Callejas A. et al. Fin isolation of cryptococcos neoformans var. gatti, serotype C, from the environment in Columbia. Med Mycol. 36:341-344.
- Chakrabati A. et al 1997. Isolation of cryptococcus neoformans var.gatti from Eucalyptus camaldulensis in India. J. Clin. Microbiol. 35: 3440-3442.
- Collier L. et al. 1998. Topley and Wilson’s Microbiology and Microbial infections. 9th ed, vol.4. Arnold, London, Sydney, Auckland, New York.
