The nucleotide sequence of the 5.8S rRNA gene and the flanked internal transcribed spacer (ITS) regions of six Trichomonas vaginalis isolates with different metronidazole sensitivity and geographic origin were genotyped. A multiple sequence alignment was performed with different sequences of other isolates available at the GenBank/EMBL/DDBJ databases, which revealed 5 different sequence patterns. Although a stablemutation in position 66 of the ITS1 (C66T)was observed in 26% (9/34) of the T. vaginalis sequences analyzed, therewas 99.7% ITS nucleotide sequence identity among isolates for this sequence. The nucleotide sequence variation among other species of the genus Trichomonas ranged from 3.4% to 9.1%. Surprisingly, the % identity between T. vaginalis and Pentatrichomonas hominis was ~83%. There was N40% divergence in the ITS sequence between T. vaginalis
and Tritrichomonas spp., including Tritrichomonas augusta, Tritrichomonasmuris, and Tritrichomonas nonconforma
and with Tetratrichomonas prowazeki. Dendrograms grouped the trichomonadid sequences in robust clades according
to their genera. The absence of nucleotide divergence in the hypervariable ITS regions between
T. vaginalis isolates suggests the early divergence of the parasite. Importantly, these data show this ITS1-5.8S
rRNA-ITS2 region suitable for inter-species differentiation.