In vitro activity of the polyether ionophorous antibiotic monensin againstthe cyst form of Toxoplasma gondii

We have studied the activity of the polyether ionophorous antibiotic monens in against the cyst form (bradyzoite) of Toxoplasma gondii. The experiments were conducted in vitro using 2 methods; cysts produced either in mice or in cell culture were exposed to monensin in vitro, and the infectivity of t he parasites was then assessed in vivo or in vitro. The data obtained from these 2 systems of evaluation showed that monensin inhibits the infectivity and the viability of the bradyzoites. Its activity was time and concentrat ion dependent. The first effects were observed at very low drug concentrati ons (i,e. 0.0001 mug/ml). Immunofluorescence and electron microscopy analys is showed significant cytological alterations of the monensin-treated brady zoites: they were swollen, had a large number of vacuoles in their cytoplas m and were found lysed at higher concentrations in ionophore.