Effect of chlorine on survival and ultrastructural changes of Acanthamoeba castellanii

Abstract Chlorine is an effective disinfection agent to kill pathogenic microorganisms in the municipal water treatment system. However, despite treatment, studies have shown that Acanthamoeba is isolated from different water sources in Iran. In this study, the effect of standard concentrations of chlorine used in urban water treatment systems was evaluated on the survival of Acanthamoeba castellanii and its ultrastructure. Acanthamoeba trophozoites and cysts were exposed to different concentrations (1-10 ppm) of calcium hypochlorite at different times (30 minutes, 1 and 2 hours). Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) were used to study the ultrastructural changes of amoebic trophozoite. This study showed that conventional chlorine concentrations could not completely eliminate A. castellanii trophozoites and cysts. Cysts were more resistant to different chlorine concentrations and compared to trophozoites, fewer cysts were killed at the same chlorine concentration and exposure time. Alteration of the cell membrane permeability, decrease in the number of pseudopodia, increase in mitochondria, vacuolation of the cytoplasm, and changes in the endoplasmic reticulum were the main ultrastructural changes in the chlorine-treated amoeba. This study showed that standard chlorine concentrations used as a disinfectant could not eliminate the trophozoites and cysts of A. castellanii. Due to the pathogenicity of the amoeba and its role as the reservoir and transmission of microbial agents, revising the guidelines for using disinfectants such as chlorine in the treatment of urban water systems is highlighted by this study.