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Acanthamoeba polyphaga

Acanthamoeba species such as Acanthamoeba polyphaga (and their close relative Naegleria fowleri) are pathogenic free-living amoebae, i.e. opportunistic rather than obligate pathogens. These organisms are ubiquitous in the environment, in soil, water and air. Acanthamoeba is characterised by a feeding and dividing trophozoite that, in response to adverse conditions, can form a dormant cyst stage:

Acanthamoeba is pathogenic to humans causing a rare but fatal encephalitis (infection of the brain) in the immunocompromised host and, more frequently, a potentially blinding infection of the cornea (keratitis). Prior to 1980's, amoebae had been reported from eye (ocular) infections only rarely - these cases were associated with trauma to the eye. In mid 1980's cases began to occur in wearers of contact lenses. Contact lens wearers are most at risk from acanthamoeba keratitis and account for 95% of reported cases. Poor hygiene practices such as failing to clean and disinfect lenses and rinsing them in tap water are known risk factors.

Acanthamoeba cysts

Non-motile cysts formed by Acanthamoeba (seen at the beginning of the video) are resistant to some disinfectants but can be killed by heat (e.g. 65°C for 30 minutes).

Ocular amoebic keratitis may be diagnosed by culturing corneal scrapings on nonnutrient agar overlaid with viable Escherichia coli.


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