الفهرس 
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Abstract
Free-living amoebae are ubiquitous group of sarcodines distributed in nature. Members of genus Acanthamoeba constitute the most abundant group of free-living amoebae that are widely distributed in the environment, especially in water.
In the present work, 48 water samples collected from inlet and outlet water at Damanhour DWTP, Behera, Egypt. Water samples were concentrated by filtration and free-living amoebae were isolated by cultivation on NN agar medium. Acanthamoeba species were morphologically identified and confirmed by PCR and sequencing. The effects of chlorine and ozone on each of the 4 molecularly identified isolates of Acanthamoeba were separately done. Two experiments were done for each Acanthamoeba genotype; one for the cyst form and the other for the trophozoite form. Three trials were performed for each experiment on each Acanthamoeba genotype and the mean result of the three trials was calculated herein.
Examination of water samples, during the period from October 2015 to September 2016, revealed the presence of Acanthamoeba species in 62.5% of the inlet water samples (raw surface water entering DWTP), while only 16.7% of the outlet drinking water samples (completely treated and chlorinated drinking water leaving DWTP) contained Acanthamoeba.
According to the seasonal variation, it was observed that Acanthamoeba species were found in the inlet water samples in a percentage of 66.7% in both of spring and autumn seasons, followed by 33.3% in winter, while the maximum occurrence was observed in summer reaching 83.3%. Consequently, the occurrence of Acanthamoeba species in the outlet drinking water samples reached 33.3% in both of spring and summer seasons, while they were completely absent in the outlet samples collected in both winter and autumn.
Molecular identification and characterization of the detected Acanthamoeba isolates from finished water samples revealed that these isolates were belonging to 4 different Acanthamoeba genotypes namely T3, T4, T15 and Acanthamoeba lenticulata.
Experimental results revealed that Acanthamoeba lenticulata trophozoites were more sensitive to chlorine (where all trophozoites, exposed to chlorine concentration 7ppm for 50 min, were found dead when tested by culture method) than the other 3 species. Acanthamoeba genotype T4 trophozoites were more resistant to chlorine (where all trophozoites, exposed to chlorine concentration 14ppm for 70 min, were found dead when tested by culture method) than the other 3 species.
Acanthamoeba lenticulata cysts were more sensitive to chlorine (where all cysts, exposed to chlorine concentration 350ppm for 110 min, were found dead when tested by culture method) than the other 3 species. Acanthamoeba genotype T15 cysts were more resistant to chlorine (where all cysts, exposed to chlorine concentration 500pm for 150 min, were found dead when tested by culture method) than the other 3 species.
Trophozoites of Acanthamoeba lenticulata were more sensitive to ozone (where all trophozoites, exposed to ozone for 3 min, were found dead when tested by culture method) than the other 3 species. Acanthamoeba genotype T4 trophozoites were more resistant to ozone (where all trophozoites, exposed to ozone for 6 min, were found dead when tested by culture method) than the other 3 species.
Cysts of Acanthamoeba genotype T15 were more sensitive to ozone (where all cysts, exposed to ozone for 35 min, were found dead when tested by culture method) than the other 3 species. Cysts of Acanthamoeba genotype T4 were more resistant to ozone (where all cysts, exposed to ozone for 65 min, were found dead when tested by culture method) than the other 3 species.