Genotyping of European Toxoplasma gondii strains by a new high-resolution next-generation sequencing-based method

Abstract

Purpose A new high-resolution next-generation sequencing (NGS)-based method was established to type closely related European type II Toxoplasma gondii strains.Methods T. gondii feld isolates were collected from diferent parts of Europe and assessed by whole genome sequencing (WGS). In comparison to ME49 (a type II reference strain), highly polymorphic regions (HPRs) were identifed, showing a considerable number of single nucleotide polymorphisms (SNPs). After confrmation by Sanger sequencing, 18 HPRs were used to design a primer panel for multiplex PCR to establish a multilocus Ion AmpliSeq typing method. Toxoplasma gondiiisolates and T. gondii present in clinical samples were typed with the new method. The sensitivity of the method was testedwith serially diluted reference DNA samples.Results Among type II specimens, the method could diferentiate the same number of haplotypes as the reference standard, microsatellite (MS) typing. Passages of the same isolates and specimens originating from abortion outbreaks were identifedas identical. In addition, seven diferent genotypes, two atypical and two recombinant specimens were clearly distinguishedfrom each other by the method. Furthermore, almost all SNPs detected by the Ion AmpliSeq method corresponded to those expected based on WGS. By testing serially diluted DNA samples, the method exhibited a similar analytical sensitivity asMS typing.Conclusion The new method can distinguish diferent T. gondii genotypes and detect intra-genotype variability among European type II T. gondii strains. Furthermore, with WGS data additional target regions can be added to the method topotentially increase typing resolution.