Induction of sulfadiazine resistance in vitro in Toxoplasma gondii

We induced sulfadiazine resistance in two sulfadiazine sensitive strains of Toxoplasma gondii, RH (Type I) and ME-49 (Type II) in vitro by using drug pressure. At first, sulfadiazine susceptibility of the two sensitive strains and two naturally resistant strains of T. gondii was evaluated on Vero cells using an enzyme-linked immunosorbent assay (ELISA). The IC50 values of sulfadiazine were 77 mu g/mL for RH, 51 mu g/rnL for ME-49 and higher than 1000 mu g/mL for the two natural resistant strains. Secondly, induced resistance of the strains by gradually increase sulfadiazine concentration was verified by this test, which resulted IC50 values at higher than 1000 mu g/mL. In conclusion we developed in vitro two sulfadiazine resistant strains called RH-R-SDZ and ME-49-R-SDZ. These strains resistant to sulfadiazine would be useful to characterize resistance mechanisms to sulfadiazine. (C) 2012 Elsevier Inc. All rights reserved.