Separation of toxoplasma cysts from brain tissue and liberation of viable bradyzoites.

A method was developed to separate Toxoplasma gondii cysts from mouse brain tissue and to liberate intact bradyzoites from cysts. Brains were blended in a Waring blender with 20% dextran solution and the homogenate was centrifuged at 4,000 g for 10 min. Cysts present in the sediment were digested by adding an equal amount of a solution containing 1 g NaCl, 1.4 ml HCl, and 1 mg pepsin (1:60,000 assay activity) per 100 ml water, and incubated at 37 C for 1 min. This method is harmless for bradyzoites, as tested by bioassays in mice. It compares favorably with published methods for separating cysts that require 3 centrifugations to achieve similar results.