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New Bioassay System for Evaluating Per Cent Survival of Entamoeba histolytica Cysts

Richard P. Stringer

The Journal of Parasitology

Vol. 58, No. 2 (Apr., 1972), pp. 306-310

Published by: Allen Press on behalf of The American Society of Parasitologists

DOI: 10.2307/3278094

Stable URL: http://www.jstor.org/stable/3278094

Page Count: 5

Abstract

Excysting Entamoeba histolytica trophozoites shed a translucent cyst wall which can easily be distinguished from the intact cyst under high-dry magnification of a microscope. A new cyst bioassay system is based on the assumption that an empty cyst represents an ameba which was alive and excysted, in contrast to a full cyst which represents a dead ameba or one unable to excyst. Live amebae can be stimulated to excyst by incubating them at 37 C in a monophasic nutrient medium. The percentage of live cysts in a population can then be calculated from a count of the full and empty forms in a drop of the excystation culture which is transferred to a slide, covered with a cover slip, and microscopically examined. The unique aspects of the bioassay system are that it makes it possible for cyst survival to be expressed as a percentage of the total number of cysts in a sample, and for the results from any test to be corrected for control cysts. This new bioassay system has been utilized successfully in studies designed to evaluate the ability of E. histolytica cysts from a variety of sources to survive exposure to halogen disinfectants and storage at various temperatures and relative humidities.

hello, you can use trypan blue and count on a neubauer chamber or you can use propidium iodide for flow cytometer. I used trypan blue is easy and cheap.

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