Acanthamoeba
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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.
Acanthamoeba as a human pathogen
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. The former is a rare disease where amoebae invade the cornea of the eye. In the United States, it is nearly always associated with contact lens use, as Acanthamoeba can survive in the space between the lens and the eye.[2][3][4][5] However, elsewhere in the world, many cases of Acanthamoeba present in non-contact lens wearers.[6] For this reason, contact lenses must be properly disinfected before wearing, and should be removed when swimming or surfing.
To detect Acanthamoeba on a contact lens in a laboratory, a sheep blood agar plate with a layer (a lawn) of E. coli is made. Part of the contact lens is placed on the agar plate. If Acanthamoeba are present, they will ingest the bacteria, leaving a clear patch on the plate around the area of the lens. Polymerase chain reaction can also be used to confirm a diagnosis of Acanthamoeba keratitis, especially when contact lenses are not involved.[7]
Acanthamoeba and 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."[8] It has been observed that Acanthamoeba can increase MRSA numbers by 1000-fold.[9]
Importance of Acanthamoeba 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[10] and probably contributes to the break down of organic matter in soil, contributing to the microbial loop.
Acanthamoeba 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.
A. astronyxis*
A. castellanii*
A. comandoni
A. culbertsoni*
A. divionensis
A. griffini
A. hatchetti*
A. healyi
A. jacobsi
A. lenticulata
A. lugdunensis*
A. mauritaniensis
A. palestinensis*
A. pearcei
A. polyphaga*
A. pustulosa
A. quina*
A. rhysodes*
A. royreba
A. terricola
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.[11] The exact nature of these symbionts and the benefit they represent for the amoebal host still have to be clarified.
Life Cycles
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Description
Adapted from CDC
See also
References
- Khan, N. A. (2006) Acanthamoeba: biology and increasing importance in human health. Fems Microbiology Reviews 30, 564-595.
- ↑ Di Gregorio, C (1992). "Acanthamoeba meningoencephalitis in a patient with acquired immunodeficiency syndrome". Archives of Pathology & Laboratory Medicine. 116 (12): 1363–5. PMID 1456885. Unknown parameter
|month=ignored (help); Unknown parameter|coauthors=ignored (help);|access-date=requires|url=(help) - ↑ Auran, JD (1987). "Acanthamoeba keratitis. A review of the literature". Cornea. 6 (1): 2–26. PMID 3556011. Unknown parameter
|coauthors=ignored (help);|access-date=requires|url=(help) - ↑ JOHN D.T. (1993) Opportunistically pathogenic free-living amebae. In: J.P. Kreier and J.R. Baker (Eds.), Parasitic Protozoa. Vol. 3. Academic Press, New York, pp. 143–246.
- ↑ Badenoch, PR (1995). "Corneal virulence, cytopathic effect on human keratocytes and genetic characterization of Acanthamoeba". International journal for parasitology. 25 (2): 229–39. PMID 7622330. Unknown parameter
|month=ignored (help); Unknown parameter|coauthors=ignored (help);|access-date=requires|url=(help) - ↑ Niederkorn, JY (1999). "The pathogenesis of Acanthamoeba keratitis". Microbes and Infection. 1 (6): 437–43. PMID 10602676. Unknown parameter
|month=ignored (help); Unknown parameter|coauthors=ignored (help);|access-date=requires|url=(help) - ↑ Sharma S, Garg P, Rao GN. "Patient characteristics, diagnosis, and treatment of non-contact lens related Acanthamoeba keratitis." The British Journal of Ophthalmology. 2000 Oct;84(10):1103-8. PMID: 11004092
- ↑ Pasricha, Gunisha (2003). "Use of 18S rRNA Gene-Based PCR Assay for Diagnosis of Acanthamoeba Keratitis in Non-Contact Lens Wearers in India". Journal of Clinical Microbiology. 41 (7): 3206–3211. doi: 10.1128/JCM.41.7.3206-3211.2003. Unknown parameter
|coauthors=ignored (help); Unknown parameter|month=ignored (help) - ↑ "MRSA use amoeba to spread, sidestepping hospital protection measures, new research shows" (Press release). University of Bath. 2006-02-28. Retrieved 2007-02-12.
- ↑ "Single Cell Amoeba Increases MRSA Numbers One Thousand Fold" (Press release). Blackwell Publishing. 2006-03-01. Retrieved 2007-02-12.
- ↑ Anderson, I. J. (2005). "Gene Discovery in the Acanthamoeba castellanii Genome". Protist. 156 (2): 203–14. PMID 16171187. Unknown parameter
|month=ignored (help); Unknown parameter|coauthors=ignored (help);|access-date=requires|url=(help) - ↑ Horn, M (2004). "Bacterial Endosymbionts of Free-living Amoebae". Journal of Eukaryotic Microbiology. 51 (5): 509–14. PMID 15537084. Unknown parameter
|month=ignored (help); Unknown parameter|coauthors=ignored (help);|access-date=requires|url=(help)
External links
- Acanthamoeba spp. as Agents of Disease in Humans - Clinical Microbiology Reviews, accessed on 4th February 2006
- Comprehensive resource on Amoeba -
- Eye health and Acanthamoeba