Research Article: Genetic Polymorphisms and Phenotypic Profiles of Sulfadiazine-Resistant and Sensitive Toxoplasma gondii Isolates Obtained from Newborns with Congenital Toxoplasmosis in Minas Gerais, Brazil

Date Published: January 24, 2017

Publisher: Public Library of Science

Author(s): Letícia Azevedo Silva, João Luís Reis-Cunha, Daniella Castanheira Bartholomeu, Ricardo Wagner Almeida Vítor, Herbert B. Tanowitz.


Previous Toxoplasma gondii studies revealed that mutations in the dhps (dihydropteroate synthase) gene are associated with resistance to sulfonamides. Although Brazilian strains are genotypically different, very limited data are available regarding the susceptibility of strains obtained from human to sulfonamides. The aim of this study was to evaluate the efficacy of sulfadiazine (SDZ) against Brazilian isolates of T. gondii and verify whether isolates present polymorphisms in the dhps gene. We also investigated whether the virulence-phenotype and/or genotype were associated with the profile of susceptibility to SDZ.

Five T. gondii isolates obtained from newborns with congenital toxoplasmosis were used to verify susceptibility. Mice were infected with 104 tachyzoites and orally treated with different doses of SDZ. The mortality curve was evaluated by the Log-rank test. The presence of polymorphisms in the dhps gene was verified using sequencing. A descriptive analysis for 11 Brazilian isolates was used to assess the association between susceptibility, genotype, and virulence-phenotype.

Statistical analysis showed that TgCTBr03, 07, 08, and 16 isolates were susceptible to SDZ, whereas TgCTBr11 isolate presented a profile of resistance to SDZ. Nineteen polymorphisms were identified in dhps exons. Seven polymorphisms corresponded to non-synonymous mutations, with four being new mutations, described for the first time in this study. No association was found between the profile of susceptibility and the virulence-phenotype or genotype of the parasite.

There is a high variability in the susceptibilities of Brazilian T. gondii strains to SDZ, with evidence of drug resistance. Despite the large number of polymorphisms identified, the profile of susceptibility to SDZ was not associated with any of the dhps variants identified in this study. Other genetic factors, not yet determined, may be associated with the resistance to SDZ; thus, further studies are needed as a basis for a more adequate toxoplasmosis treatment.

Partial Text

Toxoplasma gondii is an obligate intracellular protozoan parasite distributed worldwide that infects a wide range of warm-blooded animals [1]. Infection in humans is usually asymptomatic, but a severe manifestation can occur in cases of congenital toxoplasmosis and immune-compromised individuals, with treatment being indicated in such cases [1].

Despite the fact that the Brazilian T. gondii strains are genetically and phenotypically different from the type I, II, and III clonal strains found in Europe and North America, very few studies have evaluated the response of the Brazilian strains to treatment with extensively prescribed drugs, such as sulfadiazine. There are only two studies conducted with Brazilian strains of T. gondii that verified the effect of SDZ [14, 18]. In both the authors found that the susceptibility of T. gondii to SDZ in in vivo models varied according to the parasite strain. However, the genetic factors that could be associated with these differences in T. gondii isolates obtained from humans had not yet been investigated.

This is the first study that evaluates the susceptibility to SDZ of T. gondii obtained from newborns with congenital toxoplasmosis in Brazil, and verifies whether the identified profile of susceptibility is related to mutations in the dhps gene. It is also the first study that evaluates the association between the genotype or virulence-phenotype and the susceptibility profile of the parasite. This study confirms the existence of a Brazilian T. gondii isolate obtained from human infection, which is resistant to SDZ. We found that the profile of susceptibility to SDZ is probably not associated with the presence of polymorphisms in the dhps gene. Further studies, using a large number of Brazilian T. gondii isolates, must be conducted to confirm these findings.




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