Abstract: 　Objective To investigate the cytotoxic effect(CTE) on human cervix cancer HeLa cells induced by five strains of pathogenic free living Acanthamoeba .Methods The cytotoxic effect of five isolates of Acanthamoeba on HeLa cells was investigated by light microscopy and MTT method.Results The photomicrographs of HeLa cells showed a sequence of cardinal morphological features of apoptosis when HeLa cells were exposed to Acanthamoeba in a time dependent manner at a ratio of 1∶1 for 12 h. MTT method showed more than 50% of tumor cells underwent cytolysis following exposure to A lugdunensis trophozoites,and only 18% of cells treated with A polyphaga underwent CTE. The CTE produced by A lugdunensis and A quina trophozoites was more rapid than the others, beginning as early as 6 h after coincubation and resulting in cytolysis by 72 h.Conclusion These five strains of Acanthamoeba exhibit cytotoxic effects of varying degrees on HeLa cells,inducing apoptosis.

Key words: Acanthamoeba, tumor cell, cytotoxic effect, apoptosis