Simultaneous growth and mass encystation of Entamoeba invadens under axenic conditions.

Encystation of Entamoeba invadens IP-1 strain trophozoites was induced in low glucose medium (LG). The numbers of trophozoites, cysts and nuclei per cyst were determined; excystation of detergent-resistant axenic cysts was induced in both BI-S-33 and LG media. It was found that after 48 and 72 h of incubation in LG, cyst production was higher than trophozoites inoculated, 90 and 65% of those cysts being morphologically viable, respectively, as differentiation proceeded cysts became tri- and tetranucleated.E. invadens cysts were able to excyst either in BI-S-33 or LG media. There were no differences in growth kinetics when amebic cultures from cysts excysted in BI-S-33 were compared with parent strain. On the contrary, lower yields of trophozoites were achieved with amebas excysted and further cultured in LG medium, but they were able to grow and simultaneously undergo mass encystation. This, as well as other evidence, suggests that E. invadens trophozoites are able to modulate their physiology according to the nutrients and other factors available in the medium, in order to accomplish, growth, encystation or simultaneous growth and mass encystation. Induction of life cycle of pathogenic amebas under axenic conditions can provide answers to inhibit encystment and/or excystment.