Intergenic spacer (IGS) polymorphism: A new genetic marker for differentiation of Toxoplasma gondii strains and Neospora caninum

The region between the 28S and 18S rRNA genes, including the intergenic spa cer (IGS) region and the 5S rRNA gene, from 32 strains of Toxoplasma gondii and the NC1 strain of Neospora caninum was amplified and used for DNA sequ encing and/or restriction fragment length polymorphism (RFLP) analysis. The 5S rDNA sequences from 20 strains of T. gondii were identical. The IGS reg ion between the 5S and 18S rRNA genes (nontranscribed spacer 2 or NTS 2) sh owed 10 nucleotide variations. Six of the 10 variant positions correlated w ith the murine virulence of the strains. Intraspecific polymorphisms distin guished the virulent strains of zymodemes 5, 6, and 8 from other virulent s trains tin zymodeme 1). RFLP methods (IGS-RFLP) were developed and used to characterize the virulent and avirulent patterns among 29 T. gondii strains . Sequence diversity of 19.8% was found between T. gondii and N. caninum wh en comparing a region of 919 bp at the 3' end of NTS 2. The sequence variat ion in ribosomal IGS could therefore be a useful marker for Toxoplasma stra in identification and for distinguishing N. caninum from T. gondii.