Cryptococcus neoformans
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Cryptococcus neoformans |
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| ( San Felice ) Vuill. |
Cryptococcus neoformans is a yeast-like , encapsulated fungus with worldwide distribution. The species is 1 to 5 µm in size, rounded and has a haploid set of chromosomes. The sexual or teleomorphic stage of Cryptococcus neoformans is called Filobasidiella neoformans and was described in 1976 by Kwon-Chung.
Cryptococcus neoformans is the most important causative agent of cryptococcosis , an opportunistic infection that almost always occurs in patients with severe immunodeficiency . Cryptococcosis is one of the most important AIDS- defining diseases.
Occurrence
Cryptococcus neoformans occurs worldwide. It grows in the ground and on various grasses and cereals . The fungus can often be found in the droppings of various bird species. The resulting dusts represent a source of infection for humans. Serological evidence of contact with Cryptococcus neoformans is common among healthy people . The infection usually occurs in childhood and either leads to elimination of the pathogen or to an asymptomatic latency stage. As a pathogen in humans, Cryptococcus neoformans occurs almost exclusively in people with reduced immune system performance. This applies to AIDS patients and patients on immunosuppressive therapy. Projections come to the conclusion that around 1 million people develop cryptococcosis every year and around 600,000 die. The majority of the cases are related to the HIV epidemic that has raged since the early 1990s.
Disease emergence
The fungus enters the human body through the respiratory tract . In immunocompetent people, Cryptococcus neoformans eliminates the pathogen or the pathogen is encapsulated by the immune system in a granuloma . Nothing is known about the consequences of latent infection in humans. In the animal model, however, a connection with allergic respiratory diseases could be shown. In people with immunodeficiency, the pathogen can penetrate the blood and cross the blood-brain barrier . The majority of illnesses are seen as a reactivation of a latent infection. Around 20% are attacked by several strains and are assessed as new infections from the environment. Possible mechanisms for this are a direct overcoming of the barrier by fungal cells and the introduction by macrophages infected with Cryptococcus neoformans . As soon as the pathogen has penetrated the central nervous system, it induces meningitis through its multiplication . The pathogen protects its polysaccharide capsule against phagocytosis . Large amounts of capsular polysaccharides, which disrupt the immune response, are also released into the tissue. The fungus also produces enzymes (including a phospholipase) to break down the host's tissues.
For the more dangerous form, see the mutated fungus Cryptococcus neoformans var. Gattii and Cryptococcus gattii .
treatment
The antimycotics amphotericin B and flucytosine as well as the group of azoles ( fluconazole , voriconazole , posaconazole , itraconazole and others) are available for treating the disease . These are given in combinations depending on the severity of the disease. After healing, a multi-year or lifelong maintenance therapy is usually necessary.
metabolism
On May 23, 2007, a scientific work was published under the direction of Arturo Casadevall, which deals with fungi , including Cryptococcus neoformans , which probably convert ionizing radiation into energy usable for their organism by means of melanin . This results in some interesting approaches:
- Melanin-containing fungi are unsuitable for the direct disposal of nuclear waste , as they only partially convert the radiation produced by the radioactive isotopes into chemical energy and do not break down the isotopes themselves. Of interest, however, are the implications that arise for the recycling of nuclear waste by means of mushrooms.
- It is conceivable that with the help of such mushrooms food for astronauts can be produced during a space flight . Everywhere in space there is more cosmic radiation than light that can be used by plants.
- The question also arises as to how large the proportion of biomass or energy is that is generated by processes in which melanin plays a central role. Since the biomass produced by fungi on our planet is larger than that produced by plants through photosynthesis , it may be that that produced by processes with a central role of melanin is even the larger part.
It is expressly emphasized that the role of melanin in energy production is still unclear. The only thing that is clear is that the fungi from samples from the sealed Chernobyl nuclear reactor :
- a higher metabolic rate was given when they were fortified with melanin than with untreated mushrooms.
- Changes in the electron configuration of the electron shell of their melanin were detected during energy generation . This indicates a changed energy level that is to be expected when generating energy.
- an increased fourfold reduction of NAD + can be observed when radioactive irradiated. This is a metabolic process.
- The metabolism of Wangiella dermatitidis and Cryptococcus neoformans was significantly more active when exposed to radiation of around five hundred times the natural radiation exposure than under normal conditions.
Research history
Cryptococcus neoformans was first described in 1890.
Individual evidence
- ^ Herbert Hof, Rüdiger Dörries: Medical Microbiology , 3rd Edition, Stuttgart, 2005, p. 479.
- ↑ a b c d Arturo Casadevall: Cryptococcosis , in Dan L. Longo, Anthony A. Fauci, Dennis Kasper, Stephen L. Hauser, J. Larry Jameson, Joseph Localzo: Harrison's Principles of Internal Medicine , 18th Edition, New York, 2012, pp. 1648-1651.
- ↑ Desnos-Ollivier, M. et al .: Mixed Infections and In Vivo Evolution in the Human Fungal Pathogen Cryptococcus neoformans . In: MBio . 18, No. 1, 2010, p. E00091-10. PMID 20689742 .
- ↑ IDSA Guideline: John R. Perfect et al. : Clinical Practice Guidelines for the Management of Cryptococcal Disease: 2010 Update by the Infectious Diseases Society of America. , Clin Infect Dis. (2010) 50 (3): 291-322 doi : 10.1086 / 649858
- ↑ Ekaterina Dadachova, Ruth A. Bryan, Xianchun Huang, Tiffany Moadel, Andrew D. Schweitzer, Philip Aisen, Joshua D. Nosanchuk, Arturo Casadevall: Ionizing Radiation Changes the Electronic Properties of Melanin and Enhances the Growth of Melanized Fungi. In: PLoS ONE. 2, 2007, p. E457, doi : 10.1371 / journal.pone.0000457 .
Web links
- Cryptococcus neoformans ( Memento from April 24, 2013 in the Internet Archive ) on schimmel-schimmelpilze.de
- Cryptococcus neoformans - data set in the index Fungorum
