In Vitro Susceptibility of Various Genotypic Strains of Toxoplasma gondii to Pyrimethamine, Sulfadiazine, and Atovaquone

Abstract

Sulfadiazine, pyrimethamine, and atovaquone are widely used for the treatment of severe toxoplasmosis. Their in vitro activities have been almost exclusively demonstrated on laboratory strains belonging to genotype I. We determined the in vitro activities of these drugs against 17 strains of Toxoplasma gondii belonging to various genotypes and examined the correlations among 50% inhibitory concentrations (IC 50 s), growth kinetics, strain genotypes, and mutations on drug target genes. Growth kinetics were determined in THP-1 cell cultures using real-time PCR. IC 50 s were determined in MRC-5 cell cultures using a T. gondii-specific enzyme-linked immunosorbent assay performed on cultures. Mutations in dihydrofolate reductase (DHFR), dihydropteroate synthase (DHPS), and cytochrome b genes were determined by sequencing. Pyrimethamine IC 50 s ranged between 0.07 and 0.39 mg/liter, with no correlation with the strain genotype but a significant correlation with growth kinetics. Several mutations found on the DHFR gene were not linked to lower susceptibility. Atovaquone IC 50 s were in a narrow range of concentrations (mean, 0.06 ؎ 0.02 mg/liter); no mutation was found on the cytochrome b gene. IC 50 s for sulfadiazine ranged between 3 and 18.9 mg/liter for 13 strains and were >50 mg/liter for three strains. High IC 50 s were not correlated to strain genotypes or growth kinetics. A new mutation of the DHPS gene was demonstrated in one of these strains. In conclusion, we found variability in the susceptibilities of T. gondii strains to pyrimethamine and atovaquone, with no evidence of drug resistance. A higher variability was found for sulfadiazine, with a possible resistance of three strains. No relationship was found between drug susceptibility and strain genotype.

Transmission ofToxoplasma gondiifrom Infected Dendritic Cells to Natural Killer Cells

“…We next determined if lysis of infected DC was related to parasite replication. Inhibition of tachyzoite replication was performed by pretreatment of DC and freshly egressed tachyzoites with pyrimethamine that was maintained throughout the experiment (30). Infected DC were still hypersensitive to NK cell-mediated lysis (Fig.…”

Great efficacy of sulfachloropyrazine-sodium against acute murine toxoplasmosis

“…Many types of sulfonamides have been applied clinically (e.g., sulfathiazole, sulfamethoxazole, sulfamethazine, SD, sulfabenzamide, sulfamethizole, sulfisoxazole, sulfapyridine, sulfamerazine, sulfacetamide, sulfanilamide, sulfadoxine, sulfinpyrazone, sulfadimethoxine), but little effectiveness has been reported against parasites [11,22] . Pyrimethamine plus SD are routinely used for drug screening [13,14,[23][24][25] . The seven sulfonamides selected in this study had not previously been applied to treat T. gondii infection, but had been used against other protozoan infections, such as poultry coccidiosis for many years.…”

Treating ocular toxoplasmosis: current evidence

“…It is clear that in experimental models the strain type relates to virulence, but this is not proven in man. The demonstration of infection with a more virulent strain might justify more toxic or prolonged treatment (Holland 2004) and further investigation of the genome of the different strains may predict antibiotic sensitivity (Meneceur et al 2008). Currently prospective placebo controlled trials are needed to answer whether the use of antibiotics in active ocular disease is doing more harm than good and to compare the effect of concomitantly administered corticosteroids.…”