In Vitro Assessment of Antimicrobial Agents Against Toxoplasma gondii

Abstract

We have modified a method of quantitating growth of Toxoplasma organisms by measuring incorporation of [³H]uracil into Toxoplasma-infected, differentiated L₆E₉ rat myocytes and have found that low-dose pyrimethamine (0.1 μg/ml) and sulfadiazine (25 μg/ml) are synergistic. Pyrimethamine at higher concentrations (0.5 and 1.0 μg/ml) inhibits uptake to the same degree as the low-dose pyrimethamine-sulfadiazine combination. Spiramycin was effective only at high concentrations (200 μg/ml) and with prolonged incubation of >72 h. Clindamycin and several of its analogues, methotrexate and difluoromethylornithine, were all ineffective and showed no additive effect with either pyrimethamine or sulfadiazine. Spirogermanium, an experimental antineoplastic and anti protozoan agent, was effective only at concentrations close to those toxic to the system. 5-Fluorouracil was effectiveeven at 0.1 μg/ml. At 0.01 μg/ml it was synergistic with pyrimethamine (0.1 μg/ml), and the combination was as effective as high-dose pyrimethamine (1.0 μg/ml).