Excystation of coccidian oocysts is accomplished in vitro by altering wall permeability with CO2 and a reducing agent, then activating the enclosed sporozoites with a solution of trypsin and bile. Elucidation of the mechanism of action of the CO2-reducing agent treatment was the basic intent of this study. Oocysts of Eimeria stiedae (rabbit) and E. tenella (chicken) were tested for the presence of an excystation-associated enzyme by incubating sporulated oocysts in fluids extracted from variously treated oocysts, and by carbon-14 labelling; the effect of CO2 -reducing agent treatment on oocyst walls was investigated by titration with acid or base for secondary bonding groups, or with dithionitrobenzoate (DTNB) for sulfhydryl groups. Electron microscopy was used to observe some effects of the excystation treatment. An excystation-associated enzyme was not found. Sulfhydryl groups appear to be present in the walls of both species. The DTNB titration indicated an increase in such groups with E. stiedae after outer wall removal and/or exposure to CO2-reducing agent treatment. A similar increase was not seen with E. tenella. Carbon dioxide probably acts as an allosteric affector, enabling the reducing agent to attack wall-stabilizing disulfide bonds in oocyst walls, thereby altering the permeability of the walls by reducing such bonds to sulfhydryl groups.
College and Department
Plant and Wildlife Sciences
BYU ScholarsArchive Citation
Jolley, William Ronald, "A proposed mechanism of action for in vitro excystation of two species of coccidia" (1973). Theses and Dissertations. 7793.