Objective: This study was to investigate morphological changes and fine structures of the cyst form of Acanthamoeba after treatment with various concentrations of povidone-iodine (BetadineTM) using transmission electron microscopy. Methods: Acanthamoeba spp. were isolated from patients with amebic keratitis and obtained from the cultures on 3% non- nutrient agar (NNA) plates seeded with heat killed Escherichia coli (NNA-E. coli) with incubation at 30oC for 7 days. The cysts were harvested and washed in ameba saline solution and adjusted to a final concentration of 104 cysts/ml. Various concentrations of povidone-iodine were put in the microtiter plate wells. The minimum cysticidal concentration was the lowest concentration that there was no excystment after 1 week of incubation. The cysts were prepared for routine transmission electron microscopy to determine the structural and organelle damages. Results: Structural damages were observed in the cysts treated with povidone-iodine of 0.04% dilution. Many cysts showed shrinkage of amoeba from the cyst wall and there was a slight withdrawal of the cytoplasm from the cyst wall. Many cysts were ruptured and broken into small pieces. Conclusion: Structural damages were observed in the cysts treated with 0.04% dilution of povidone-iodine solution or more than that. The damage started with pores produced in the cyst wall and the loss of water, shrinkage and loss of the cytoplasm of the inside cell from the cyst wall, followed by breaking of the cyst wall and the inside cell into small pieces.Â
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