Selection of polymorphic peptides from GRA6 and GRA7 sequences of Toxoplasma gondii strains to be used in serotyping.

International audienceToxoplasma gondii isolates obtained from other geographical environments than Europe and North America revealed the existence of atypical strains that are not included in the 3 archetypal clonal lineages (I, II, III). GRA6 and GRA7 are polymorphic genes that have been used for Toxoplasma genotyping. The coding region of GRA6 and GRA7 from 49 non-archetypal strains was sequenced and compared with type I, II and III reference strains. Eighteen and ten different amino acid sequences were found for GRA6 and GRA7 respectively. The polymorphisms found between the different sequences were analysed, with the objective to define peptides to be used in serotyping of Toxoplasma infections. Two peptides specific for clonal lineages I and III were selected from GRA7 locus (GRA7I and GRA7III). Three peptides, specific for some atypical strains were selected from both GRA6 and GRA7 loci (Am6, Af6 and Am7). Serum samples from humans infected with Toxoplasma strains with known genotype were serotyped with the selected peptides. Peptide GRA7III seems to be a good candidate for serotyping type III infections. Peptide GRA7I had a very low sensitivity. Peptides Am6 and Af6 had low specificity, since they reacted with serum samples from patients infected with strains belonging to the three archetypal lineages. Peptide Am7, although specific had low sensitivity