Acanthamoeba
| Acanthamoeba | ||||||||
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Acanthamoeba keratitis |
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| Scientific name | ||||||||
| Acanthamoeba | ||||||||
| Volkonsky , 1931 |
Acanthamoeba is a genus of amoeba that live in the ground and freshwater. They can cause infections or parasitoses in humans and other animals.
features
Acanthamoeba species occur in two phases of life: as an active, free-living amoeba, called trophozoite , with a diameter of about 13 to 23 micrometers, and as a permanent dormant phase or cyst . The name component "acanth" derived from ancient Greek Acanthos: Dorn, Stachel, refers to spike-like formations of the surface of trophozoites which Acanthopodien, a special form of pseudopodia or pseudopodia. Acanthopodia are usually relatively short, thorn- or finger-shaped protuberances of the cell body, which can be everted at any point on the cell and reabsorbed. They are important for the adhesion to surfaces, the locomotion and the feeding of the amoeba. They get their structure and shape from cytoskeletal elements, especially actin microfilaments . The amoeba are capable of rapid movement and reach speeds of up to 0.8 micrometers per second. Inside the cell body, vacuoles of various shapes and functions can be seen. Food vacuoles serve to swallow up food particles through phagocytosis , lysosomes their digestion. Contractile vacuoles are elements of osmoregulation that excrete excess water. The largest organelle, the nucleus , is usually about one sixth the size of the trophozoite. Acanthamoeba is usually mononuclear, but multinucleated cells have also been observed as a rare deviation. A special feature of the Acanthamoeba cell membrane is the biopolymer lipophosphonoglycan, a combination of amino phosphonates , galactosamine and various sugar molecules.
Adverse environmental conditions cause the trophozoite to encapsulate itself in a double-walled cyst. The outer wall of the cyst consists mainly of proteins and polysaccharides. The inner wall contains the polysaccharide cellulose . Both walls are separated from each other by a space. The encysted cell body is connected to the outside world via processes that cross both walls. These have small openings (ostioles) on the outside, which are protected in the center by lid-shaped opercula. Encapsulation is triggered by a lack of food, but also by an unsuitable chemical environment and a lack of oxygen ( hypoxia ). Cysts can survive dehydration and, under certain conditions, were still able to transform into trophozoites after 50 years. Dried out cysts are not uncommon in the ambient air and are spread with the wind. For encysting and shedding the cyst wall are u. a. Responsible for receptors that measure the nutrient content of the surrounding medium.
species
The taxonomy of the genus Acanthamoeba is confused, so that it is hardly possible to specify how many and which species exist. The type species of the genus, Acanthamoeba castellanii , was discovered (as Hartmannella castellanii ) in 1930 in a cell culture of the yeast fungus Cryptococcus pararoseus . A year later, the biologist Michel Volkonsky, doing research in Paris, re-established the genus for the species on the basis of the double-walled cyst and the tapered spindle apparatus in mitosis. Later editors denied the taxonomic value of the spindle apparatus, so that the genus was diagnosed solely on the basis of the cyst. Since the 1930s, 18 new species have been gradually described , the diagnosis of which was based solely on the shape and formation of the cysts. According to the shape of the cyst, three groups of species were established.
More modern, phylogenomic investigations (investigations of kinship relationships based on the comparison of homologous DNA sequences , especially mitochondrial DNA ) proved the monophyly of the genus. Her sister group is then the genus Balamuthia (with the only species Balamuthia mandrillaris ). Within the genus, however, the picture turned out to be unclear. It was possible to distinguish 15 sequence types on the basis of DNA, but these do not correspond to the classic types described on the basis of the cyst morphology. Of the three groups of species in classical morphology, only one turned out to be monophyletic. Numerous classical species, including the Acanthamoeba castellanii type , were polyphyletic according to DNA data. H. artificially joined groups without any closer internal relationship. The picture was further complicated by the fact that two working groups each discovered a new, but different sequence type, which they both called T16; this name is now assigned twice. In practice, therefore, today no species are normally differentiated within the genus, but the strains examined (analogous to bacterial strains) are only assigned to one of the sequence types. The picture is further complicated by the fact that the pathogenic (pathogenic) strains of Acanthamoeba are distributed widely and without regularity over the 17 sequence types. Sequence type T4 is the most common pathogen as well as the most widespread in soils.
distribution
Representatives of Acanthamoeba are widespread worldwide and can be found in all habitats (ubiquistic) in soils and in fresh and salt water biotopes , they are among the most common soil-living protists . The genus is possibly of great importance for the turnover of nutrients in soils. Although they can phagocytize and use all types of organic matter, their fundamental ecological importance lies primarily in grazing bacteria, which stimulates bacterial populations to increase their growth and metabolism. In addition, the genus is known as an opportunistic pathogen , also in humans, and has been researched in this role much more intensively.
Pathogenicity
Acanthamoeba can cause acanthamoeba keratitis , an infection of the eye. They are also the causative agents of granulomatous amoebic encephalitis , also known as acanthamoebiasis .
therapy
Parasitosis caused by Acanthamoeba can be treated with polyhexamethylene biguanide or propamidine isoethionate. In addition, neomycin - polymyxin-B -gramidine, propamidine-isothionate ointment and, if necessary, voriconazole are administered . Liposomal amphotericin B is also effective.
Others
In 2013 the genus Acanthamoeba was named single cell of the year by the German Society for Protozoology .
literature
- Frederick C. Page: Re-Definition of the Genus Acanthamoeba with Descriptions of Three Species. In: The Journal of Protozoology. 14, 1967, p. 709, doi : 10.1111 / j.1550-7408.1967.tb02066.x .
swell
- ^ A b F. Marciano-Cabral, G. Cabral: Acanthamoeba spp. as agents of disease in humans. In: Clinical microbiology reviews. Volume 16, Number 2, April 2003, pp. 273-307, PMID 12692099 , PMC 153146 (free full text) (review).
- ↑ a b Ruqaiyyah Siddiqui & Naveed Ahmed Khan (2012): Biology and pathogenesis of Acanthamoeba. Parasites & Vectors 2012 5: 6 doi : 10.1186 / 1756-3305-5-6
- ↑ David Lloyd (2014): Encystment in Acanthamoeba castellanii: A review. Experimental Parasitology 145: S20-S27. doi : 10.1016 / j.exppara.2014.03.026
- ^ GS Visvesvara (1991): Classification of Acanthamoeba. Reviews of Infectious Diseases 13, Supplement 5 (International Symposium on Acanthamoeba and the Eye): S369-S372. online at JSTOR
- ↑ Stefan Geisen, Anna Maria Fiore-Donno, Julia Walochnik, Michael Bonkowski (2014): Acanthamoeba everywhere: High diversity of Acanthamoeba in soils. Parasitology Research 113 (9): 3151-3158. doi : 10.1007 / s00436-014-3976-8
- ^ Marianne Abele-Horn: Antimicrobial Therapy. Decision support for the treatment and prophylaxis of infectious diseases. With the collaboration of Werner Heinz, Hartwig Klinker, Johann Schurz and August Stich, 2nd, revised and expanded edition. Peter Wiehl, Marburg 2009, ISBN 978-3-927219-14-4 .
- ↑ http://www.protozoologie.de/Einzellerdesjahres2012.html , accessed on March 21, 2016
