Acanthamoeba: Wikis

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Acanthamoeba
Phase contrast micrograph of an Acanthamoeba polyphaga cyst.
Scientific classification
Domain: Eukaryota
Kingdom: Amoebozoa
Genus: Acanthamoeba

Acanthamoeba is a genus of amoebae, one of the most common protozoa in soil, and also frequently found in fresh water and other habitats. The cells are small, usually 15 to 35 μm in length and oval to triangular in shape when moving. The pseudopods form a clear hemispherical lobe at the anterior, and there are various short filose extensions from the margins of the body. These give it a spiny appearance, which is what the name Acanthamoeba refers to. Cysts are common. Most species are free-living bacterivores, but some are opportunists that can cause infections in humans and other animals.

Contents

Human pathogen

Acanthamoeba encephalitis

Diseases caused by Acanthamoeba include amoebic keratitis and encephalitis.[1] The latter is caused by Acanthamoeba entering cuts and spreading to the central nervous system.

Acanthamoeba granulomatous encephalitis

This is an opportunistic protozoan pathogen that rarely causes disease in humans. Approximately 400 cases have been reported worldwide with a survival rate of only two to three percent. Infection usually occurs in patients with an immunodeficiency, diabetes, malignancies, malnutrition, systemic lupus erythematosus, or alcoholism. The parasite's portal of entry is via lesions in the skin or the upper respiratory tract or via inhalation of airborne cysts. The parasite then spreads hematogenously into the central nervous system. Acanthamoeba crosses the blood brain barrier by means that are not yet understood. Subsequent invasion of the connective tissue and induction of pro-inflammatory responses leads to neuronal damage which can be fatal within days. A post-mortem biopsy reveals severe oedema and hemorrhagic necrosis.[2] A patient that has contracted this illness usually displays subacute symptoms including altered mental status, headaches, fever, neck stiffness, seizures, focal neurological signs such as cranial nerve palsies and coma all leading to death within one week to several months.[3] Due to the rarity of this parasite and our lack of knowledge there are currently no good diagnoses or treatments for Acanthamoeba.

Infection usually mimics that of bacterial leptomeningitis, tuberculous meningitis, or viral encephalitis. The misdiagnosis often leads to erroneous treatment that is ineffective. In the case that Acanthamoeba is diagnosed correctly, the current treatments such as amphotericin-B, rifampicin, trimethroprim-sulfamethoxazole, ketokonazole, fluconazole, sulfadiazine, albendazole are only tentatively successful. Correct and timely diagnosis as well as improved treatment methods as well as understanding of the parasite are important factors in improving the outcome of infection by Acanthamoeba.

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MRSA

Methicillin-resistant Staphylococcus aureus (MRSA) is an important pathogen in the hospital setting due to its resistance to many antibiotics. Recent findings from the University of Bath demonstrate that MRSA can infect and replicate inside of Acanthamoeba polyphaga; this Acanthamoeba species is widespread throughout the environment. Since A. polyphaga can form cysts, cysts infected with MRSA can act as a mode of airborne dispersal for MRSA. Additionally, it is noted that "evidence with other pathogens suggests that pathogens that emerge from amoeba are more resistant to antibiotics and more virulent."[4] It has been observed that Acanthamoeba can increase MRSA numbers by 1000-fold.[5]

Importance in soil ecology

A. castellanii can be found at high densities in various soil ecosystems. It preys on bacteria, but also fungi and other protozoa.

This species is able to lyse bacteria and produce a wide range of enzymes such as cellulases or chitinases[6] and probably contributes to the break down of organic matter in soil, contributing to the microbial loop.

Species

Species of Acanthamoeba are distinguished mainly on the form of cysts, and include the following; those marked with an asterisk are known to cause infections.

Life cycle of the parasitic agents responsible for causing “free-living” amebic infections
  • A. astronyxis*
  • A. castellanii*
  • A. comandoni
  • A. culbertsoni*
  • A. divionensis
  • A. griffini
  • A. hatchetti*
  • A. healyi
  • A. jacobsi
  • A. keratitis*
  • A. lenticulata
  • A. lugdunensis*
  • A. mauritaniensis
  • A. palestinensis*
  • A. pearcei
  • A. polyphaga*
  • A. pustulosa
  • A. quina*
  • A. rhysodes*
  • A. royreba
  • A. terricola (renamed A.castellanii Poussard)
  • A. triangularis
  • A. tubiashi

Endosymbiontes of Acanthamoeba

Acanthamoeba sp. contain diverse bacterial endosymbionts which are similar to human pathogens. Because of this they are considered to be potential emerging human pathogens.[7] The exact nature of these symbionts and the benefit they represent for the amoebal host still have to be clarified.

These include Legionella and Legionella-like pathogens.[8]

Role as a model organism

Because Acanthamoeba does not differ greatly at the ultrastructural-level from a mammalian cell, it is an attractive model for cell biology studies. Acanthamoeba is important in cellular microbiology, environmental biology, physiology, cellular interactions, molecular biology, biochemistry, and evolutionary studies. This is due to the organism's versatile roles in the ecosystem and its ability to capture prey by phagocytosis, act as vector, reservoir for microbial pathogens, and to produce serious human infections. In addition, Acanthamoeba has been used extensively to understand the molecular biology of cell motility.[9]

Owing to its ease and economy of cultivation, the Neff strain of A. castellanii discovered in a pond in Golden Gate Park in the 1960s, has been effectively utilized as a classic model organism in the field of cell biology. From just 30 liters of simple medium inoculated with A. castellanii, approximately one kilogram of cells can be obtained after several days of aerated culture at room temperature. Pioneered in the laboratory of Dr. Edward D. Korn at the National Institutes of Health (NIH), many important biological molecules have been discovered and their pathways elucidated using the Acanthamoeba model. Dr. Thomas Dean Pollard applied this model at the NIH, Harvard Medical School, Johns Hopkins University School of Medicine, and the Salk Institute for Biological Studies to discover and characterize many proteins that are essential for cell motility not only in amoebas but in many other eukaryotic cells, especially those of the human nervous and immune systems, the developing embryo, and cancer cells.

Recall from Advanced Medical Optics

In May 2007, Advanced Medical Optics, manufacturer of Complete Moisture Plus Contact Lens Solution products, issued a voluntary recall of their Complete Moisture Plus solutions. The fear was that contact lens wearers who used Complete Moisture Plus were at higher risk than those who used other contact lens solutions to develop acanthamoeba keratitis.

The manufacturer recalled the product after the Centers For Disease Control in the United States found that 21 individuals had possibly received an acanthamoeba infection after using Complete Moisture Plus in the month prior to diagnosis. [10]

See also

References

  1. ^ Di Gregorio, C; Rivasi F, Mongiardo N, De Rienzo B, Wallace S, Visvesvara GS (December 1992). "Acanthamoeba meningoencephalitis in a patient with acquired immunodeficiency syndrome". Archives of Pathology & Laboratory Medicine 116 (12): 1363–5. PMID 1456885.  
  2. ^ Khan, N (November 2006). "Acanthamoeba invasion of the central nervous system". International Journal for Parasitology 37 (2): 131–8. doi:10.1016/j.ijpara.2006.11.010. PMID 17207487.  
  3. ^ Kaushal, V; Chhina DK, Kumar R, Pannu HS, Dhooria HPS, Chhina RS (March 2007). "Acanthamoeba Encephalitis". Indian Journal of Medical Microbiology 26 (2): 182–4. PMID 18445961.  
  4. ^ University of Bath (2006-02-28). "MRSA use amoeba to spread, sidestepping hospital protection measures, new research shows". Press release. http://www.bath.ac.uk/news/articles/releases/mrsaamoeba280206.html. Retrieved 2007-02-12.  
  5. ^ Blackwell Publishing (2006-03-01). "Single Cell Amoeba Increases MRSA Numbers One Thousand Fold". Press release. http://www.blackwellpublishing.com/press/pressitem.asp?ref=694. Retrieved 2007-02-12.  
  6. ^ Anderson, I. J.; Watkins, R. F., Samuelson, J., Spencer, D. F., Majoros, W. H., Gray, M. W. and Loftus, B. J. (August 2005). "Gene Discovery in the Acanthamoeba castellanii Genome". Protist 156 (2): 203–14. doi:10.1016/j.protis.2005.04.001. PMID 16171187.  
  7. ^ Horn, M; Wagner, M (Sep-Oct 2004). "Bacterial Endosymbionts of Free-living Amoebae". Journal of Eukaryotic Microbiology 51 (5): 509–14. doi:10.1111/j.1550-7408.2004.tb00278.x. PMID 15537084.  
  8. ^ Schuster, F.; Visvesvara, G. (2004). "Opportunistic amoebae: challenges in prophylaxis and treatment". Drug resistance updates : reviews and commentaries in antimicrobial and anticancer chemotherapy 7 (1): 41–51. doi:10.1016/j.drup.2004.01.002. PMID 15072770.   edit
  9. ^ Khan N (2009). Acanthamoeba: Biology and Pathogenesis. Caister Academic Press. ISBN 978-1-904455-43-1.  
  10. ^ http://www.amo-inc.com/pdf/pr-cmp.pdf

External links


Wikispecies

Up to date as of January 23, 2010

From Wikispecies

Taxonavigation

Main Page
Cladus: Eukaryota
Supergroup: Unikonta
Phylum: Amoebozoa
Familia: Acanthamoebidae
Genus: Acanthamoeba

Name

Acanthamoeba

Synonyms


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