Acanthamoeba spp. have been isolated from the environment in both warm and cold climates and from animals and humans in all parts of the world. They are present in different habitats, including natural and artificial water bodies, coastal sediments, soil, and air (Rodriguez-Zagaroza 1994). Tolerance to high chlorine concentrations promotes their presence in tap

Figure 8.1 Acanthamoeba spp. cysts stained with fluorescein conjugated anti-cyst wall monoclonal antibody. Bar = 10^m.

water, swimming pools, dental units, and medicinal pools. In Scandinavian countries, the presence of Acanthamoeba species has been reported in indoor swimming pools and in periodically freezing, outdoor swimming areas (Cerva and Huldt 1974; Vesaluoma et al. 1995; Brown and Cursons 1977). Acanthamoeba can be naturally infected by pathogenic bacteria which multiply and survive intracellulary. Despite the well-documented relationship with Legionella pneumophila (Rowbotham 1980), an increasing number of gram-negative endosymbionts in Acanthamoeba and other members of free-living amoebae group have been reported (Winiecka-Krusnell and Linder 2001). The significance of Acanthamoeba in maintaining and transmitting of human pathogens is not well recognized and the clinical and epidemiological relevance of bacterial infections in amoebae should be reconsidered.

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