Biological Studies on Entamoeba Histolytica: III. Induced Encystation in Several Mediums, Including an Account of a New Procedure

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Abstract
Quantitative evaluation of the several media involved measurements of the amount of inoculum, total yields of trophozoites and cysts, as well as the relative efficacy of pooling pre-encystment amebae from Cleveland and Collier''s medium versus half-strength eggyolk infusion. Max. encystment was achieved in a new medium, followed in order by the media of Kessel, Chang, Dobell, and Stone. The new medium consisted of a buffered liver-extract slant and an overlay containing double-strength eggyolk infusion (and optionally 10% horse serum) with added rice starch. The most important condition for successful encystation apparently lay in careful attenuation of amebic cultures in starch-depleted, half-strength eggyolk infusion immediately prior to inoculation into encystment media. All successful encystment responses were marked by tremendous multiplication of trophozoites culminating in encystation at the peak of growth in 48-72 hrs.; e.g., up to 5 x 106 cysts (= 70% of the culture) in 40 ml. vols. of medium. These results were confirmed with the NRS and UC strains of E. histolytica.