Cryptococcus neoformans is an opportunistic yeast that causes pulmonary cryptococcosis, atypical acute pneumonia, and chronic meningitis. This microorganism was initially thought to be a uniform species, but it was later divided into four serotypes (AD) and three varieties (neoformans, grubii, and gattii).
At present, the following divisions have been proposed: C neoformans var. grubii (serotype A) with 3 genotypes (VNI, VNII, VNB); C neoformans var. neoformans (serotype D or VNIV); and 5 other species, C. gattii, C. bacillisporus, C. deuterogattii, C. tetragattii and C. decagattii (serotypes B / C or VGI-IV).
Cryptococcus neoformans seen with Chinese ink
Although the varieties have different epidemiological characteristics, the pathogenicity itself is the same, which is why they are collectively called Cryptococcus neoformans.
It is a ubiquitous mushroom worldwide. People become infected when they breathe in the fungus, but the disease is not contagious from person to person.
Phylum: Basidiomycota
Class: Tremellomycetes
Order: Tremellales
Family: Tremellaceae
Genus: Cryptococcus
Species: neoformans
Morphology
Microscopic characteristics
Lab tests
Urease is positive in 2 hours of incubation at 35 ° C with Christense's urea agar or broth, although there are rapid urease detection tests described by Zimmer and Roberts with positive results in 10 to 30 minutes.
Another useful test is evidence of the production of a brown pigment in the presence of the substrate for phenol oxidase.
For this purpose, Satib and Senskau birdseed agar and caffeic acid are used, strongly inoculated (large inoculum) and incubated at 37 ° C for one week. The appearance of a brown to reddish or chestnut pigment is a positive pathognomonic test for C. neoformans.
They do not reduce nitrates to nitrites and assimilate glucose, maltose, sucrose, trehalose, galactose, cellobiose, xylose, raffinose and dulcitol, while they do not assimilate lactose or melibiose.
However, these tests are less reliable and have not been performed in laboratories for a long time.
Detection of capsular antigens of
Sometimes it is not possible to see yeast in samples, but this does not mean that Cryptococcus neoformans infection does not exist.
The fungus produces a large number of capsules at the pulmonary and systemic level. For this reason, the GXM capsular antigen can be dissolved and easily detected in CSF and serum with specific antisera by the latex agglutination technique.
The test can be quantifiable, making it ideal for the prognosis and evaluation of the efficacy of the treatment, although due to the traumatic nature of taking a CSF sample, it is not very feasible to repeat the examination to do this follow-up.
This is a very simple way of making the diagnosis, just like enzyme immunoassay methods.
The detection of Cryptococcus neoformans by nucleic acid probe technologies is another excellent alternative for rapid and safe identification.
Treatment
Flucytosine is effective but resistant mutants have emerged. Intravenous amphotericin B is another very effective alternative.
In meningitis it is necessary to use both drugs for several months, followed by a long course of fluconazole. 75% are cured but after treatment relapses may occur in some patients, requiring repeated therapeutic cycles.
References
- Wikipedia contributors. Filobasidiella. Wikipedia, The Free Encyclopedia. February 16, 2018, 19:39 UTC. Available at: https://en.wikipedia.org, 2018.
- "Cryptococcus neoformans." Wikipedia, The Free Encyclopedia. 28 Aug 2018, 13:28 UTC. 2 Dec 2018, 18:29
- Koneman E, Allen S, Janda W, Schreckenberger P, Winn W. (2004). Microbiological Diagnosis. (5th ed.). Argentina, Editorial Panamericana SA
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- Ryan KJ, Ray C. 2010. Sherris. Medical Microbiology, 6th edition McGraw-Hill, New York, USA
- González M, González N. Manual of Medical Microbiology. 2nd edition, Venezuela: Directorate of media and publications of the University of Carabobo; 2011.
- Maziarz EK, Perfect JR. Cryptococcosis. Infect Dis Clin North Am. 2016; 30 (1): 179-206.
- Central nervous system and Cryptococcus neoformans. N Am J Med Sci. 2013; 5 (8): 492-3.