[The utility of MTT and XTT colorimetric tests in the studies conducted in vitro with Toxoplasma gondii tachyzoites].

Tetrazolium salts are widely used as indicators of metabolic activity for both eukaryotic and prokaryotic cells. Live cells reduce the tetrazole ring in MTT or XTT salts and then a colored formazane formed can be assessed spectrophotometrically. Despite widespread use of MTT/XTT reduction tests biochemical mechanisms of the reaction are still unknown, and each test application case requires standardization of experimental conditions. In the present study we tested in vitro the utility of both MTT and XTT salts to determine the influence of selected extracellular agents for T. gondii tachyzoites and their host cells (i.e. mouse L929 fibroblasts). The results showed that MTT is reduced more intensively than XTT by host and parasite cells. The attenuation of T. gondii tachyzoites resulted in a decrease of reduction level of both tetrazolium salts, particularly of XTT. Using MTT we found also that T. gondii is not susceptible to extremely toxic substance, sodium azide. Our results confirmed a high usefulness of MTT reduction tests in numerous studies on eukaryotic cells.