Determination of the activity of sulfadiazine against Besnoitia darlingi tachyzoites in cultured cells.

The present study examined the efficacy of sulfadiazine in inhibiting tachyzoite production of Besnoitia darlingi in bovine turbinate cell cultures. A host cell lesion based assay was used to determine the effect of sulfadiazine on developing tachyzoites in 24-well plate format. Also, a cell culture flask assay was used to determine if the selected concentrations of sulfadiazine killed or only suppressed the development of B. darlingi. Sulfadiazine inhibited B. darlingi tachyzoite production by 50%, 66%, 84%, and 92% in cultures treated with 1.0 micro g ml(-1), 2.5 micro g ml(-1), 5.0 micro g ml(-1), and 7.5 micro g ml(-1), respectively. At least 99% inhibition of tachyzoite production was observed when infected cultures were treated with 10 micro g ml(-1) sulfadiazine. Cultured host cells exposed to 10 micro g ml(-1) sulfadiazine showed some signs of toxic changes. Sulfadiazine may have promise as a therapeutic agent in the treatment of other Besnoitia spp. The methods described for drug evaluation were rapid, inexpensive and allowed the concurrent assessment of the drug against the parasite and its cytotoxic effect.