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 wer e blended in a Waring blender with 20% dextran solution and the homoge nate was centrifuged at 4,000 g for 10 min. Cysts present in the sedim ent 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 fo r bradyzoites, as tested by bioassays in mice. It compares favorably w ith published methods for separating cysts that require 3 centrifugati ons to achieve similar results.