Effect of cytochalasin D on the growth, encystation, and multinucleation of Entamoeba invadens

The effect of cytochalasin D, a specific inhibitor of microfilaments, on th e growth, encystation, and multinucleation of Entamoeba invadens was examin ed. Cytochalasin D blocked the growth of axenic E. invadens strain IP-1 in a dose-dependent manner, which suggests that the drug is effective against this species of Entamoeba as well as against E. histolytica strain HM1: IMS S as previously demonstrated. Encystation of E. invadens as induced in vitr o was also inhibited by cytochalasin D. This is the first evidence of the p articipation of microfilaments in the encystation process. Concentrations o f cytochalasin D effective for the inhibition of encystation were lower tha n those effective for the inhibition of growth. Trophozoites grown with cyt ochalasin D became multinucleate; more than three nuclei per cell were obse rved in 71% of trophozoites grown in the presence of the drug as opposed to only 5% of those grown in the absence of the drug. Also, trophozoites grow n with cytochalasin D produced multinucleate cysts following their transfer to encystation medium. Encystation with cytochalasin D was more strongly i nhibited among trophozoites grown in the presence of the drug than among th ose grown in the absence of the drug. Also, encystation without cytochalasi n D was less frequently observed among trophozoites grown in the presence o f the drug than among those grown in the absence of the drug. Thus, the mul tinucleation of trophozoites induced by cytochalasin D had an inhibitory ef fect on their encystation.