Differentiation of Entamoeba: a new medium and optimal conditions for axenic encystation of E. invadens

Abstract

Nutritional and culturing requirements for efficient axenic encystation of E. invadens have been studied. A simple and reliable axenic encystation medium has been developed. It contains 0.5% tryptic digest of casein, 0.5% yeast extract, and 5% dialyzed serum in 5 mM potassium phosphate, pH 7.0. Mass encystation (avg. 70%) occurred within 30 hr when axenically growing trophozoites of E. invadens IP-1 were transferred to this medium before they entered stationary growth phase. Mass encystation of E. invadens PZ occurred similarly, but less reproducibly. Two E. histolytica strains did not encyst. Experiments established that differentiation did not depend upon changes in the external environment after amebae were transferred to encystation medium, and therefore, was inhibited by the shift from growth to encystation medium.