Chlorine is a disinfectant which can kill most harmful microorganisms ; this is the reason that chlorine is used in water treatment. Chlorination has become almost the only method used for the active disinfection of potable water supplies due to its effectiveness as a germicide. During In vitro action chlorine, the most common disinfectant used for treating drinking water and also swimming pools. Species of pathogenic free-living amoebae isolated from different water samples were used in the

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... sent study. The purpose was to ascertain the difference in chlorine sensitivity among different species of pathogenic small free-living amoebae and also to find out their occurrence is chlorine treated water. The experiment was conducted on pathogenic free-living amoebae (Naegleria fowleri and Acanthamoeba culbertsoni and A.rhysodes). The strains of amoebae selected for the experiment were PP-2 and HS-1 of N. fowleri; strains HP-1 and DS-1 of A. culbersoni; strains MS-3 and Us-2 of A.rhysodes. The concentrations of chlorine used in this study wee 0.25mg/ml, 0.50mg/ml,2.0mg/ml, 3.0mg/ml and 3.5mg/ml. From the present study, it was concluded that cysts and trophozoites of Naegleria fowleri strains can be destroyed in with application of free chlorine. But the strains of Acanthamoeba culbertsoni and A. rhysodes can only be checked in drinking water by the use of prolonged super chlorination, this condition is possible only when preparing the water for use and if there is no further contamination possible in the distribution network.