Use of Toxoplasma gondii expressing β-galactosidase for colorimetric assessment of drug activity in vitro

Abstract

A microtiter assay for drug evaluation has been developed with a strain of Toxoplasma gondii that expresses bacterial β-galactosidase. By using chlorophenol red-β-D-galactopyranoside (CPRG) as the substrate for β- galactosidase. The efficacy of a drug against the parasite can be determined with a colorimetric readout. Drugs known to have activity against T. gondii (specifically, pyrimethamine, solfadiazine, atovaquone, and clindamycin) were tested, and efficacies were determined by CPRG cleavage. The 50% inhibitory concentrations determined by the CPRG-based colorimetric assay were similar to those determined by the traditional radiolabelled uracil incorporation assay. Since CPRG is nontoxic to the parasite, viable drug-treated parasites can be obtained at the conclusion of the assay for further evaluation if desired. This assay provides a high-throughput and nonradioactive alternative for the identification of anti-T. gondii compounds.