title: Suitability of internal transcribed spacers (ITS) as markers for the population genetic structure of Blastocystis spp.
abstract: BACKGROUND
  The purpose of this study was to assess the genetic variation and differentiation of Blastocystis subtypes (STs) recovered from symptomatic children by analysing partial sequences of the small subunit rDNA gene region (SSUrDNA) and internal transcribed spacers (1 and 2) plus the 5.8S region (ITS, ITS1 + 5.8S + ITS2) and comparing with isolates from other countries.
  
  
  RESULTS
  Faecal samples from 47 Blastocystis-infected children with gastrointestinal symptoms and negative for pathogenic enterobacteria were analysed. PCR was performed on DNA from all the samples to identify Blastocystis STs, amplifying a fragment of SSUrDNA and the ITS region. The amplicons were purified and sequenced, and consensus sequences were submitted to GenBank; afterwards, SSUrDNA sequences were analysed for genetic diversity according to geographic area. Regarding the Blastocystis STs found, 51% were ST1, 23% ST2, 19% ST3 and 2% ST7. For ITS, a haplotype network tree and Bayesian inference revealed the presence of two novel variants of ST1, clustering some sequences into ST1A and ST1B. The values of nucleotide diversity (π) and haplotype polymorphism (θ) for ST1, ST2 and ST3 ranged from 0 to 1, whereas the ratio of genetic differentiation (FST)/migration index (Nm) showed the highest differentiation between Libya and Thailand-Philippines for ST2 (0.282/0.63). In contrast, a high flow gene was observed between Czech Republic-Denmark-Holland-Spain and USA-Mexico-Colombia for ST1 (0.003/84).
  
  
  CONCLUSIONS
  Our data on genetic differentiation and gene flow might explain the differences for the prevalence of Blastocystis STs. Moreover, the ITS region could be used as a genetic marker to assess genetic variation in this parasite.
authors.forename: Guiehdani
authors.initials: G
authors.lastname: Villalobos
authors.forename: Guadalupe Erendira
authors.initials: GE
authors.lastname: Orozco-Mosqueda
authors.forename: Merle
authors.initials: M
authors.lastname: Lopez-Perez
authors.forename: Eduardo
authors.initials: E
authors.lastname: Lopez-Escamilla
authors.forename: Alex
authors.initials: A
authors.lastname: Córdoba-Aguilar
authors.forename: Lucia
authors.initials: L
authors.lastname: Rangel-Gamboa
authors.forename: Angelica
authors.initials: A
authors.lastname: Olivo-Diaz
authors.forename: Mirza
authors.initials: M
authors.lastname: Romero-Valdovinos
authors.affiliation: Hospital General "Dr, Manuel Gea Gonzalez", Calzada de Tlalpan 4800, Mexico 14080, DF, Mexico. maravillap@yahoo.com.
authors.forename: Pablo
authors.initials: P
authors.lastname: Maravilla
authors.forename: Fernando
authors.initials: F
authors.lastname: Martinez-Hernandez
mesh_terms: D000293:Adolescent; D001483:Base Sequence; D016844:Blastocystis / Q000235:genetics* / Q000302:isolation & purification; D016776:Blastocystis Infections / Q000469:parasitology*; D002648:Child; D002675:Child, Preschool; D016000:Cluster Analysis; D021903:DNA, Ribosomal Spacer / Q000737:chemistry / Q000235:genetics*; D005243:Feces / Q000469:parasitology; D005260:Female; D051456:Gene Flow; D005819:Genetic Markers / Q000235:genetics; D014644:Genetic Variation; D005828:Genetics, Population; D006801:Humans; D007223:Infant; D008297:Male; D008800:Mexico; D008969:Molecular Sequence Data; D017422:Sequence Analysis, DNA
chemical_list: D021903:DNA, Ribosomal Spacer; D005819:Genetic Markers