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. 2005 Jan;43(1):348-55.
doi: 10.1128/JCM.43.1.348-355.2005.

Molecular Phylogenies of Blastocystis Isolates From Different Hosts: Implications for Genetic Diversity, Identification of Species, and Zoonosis

Free PMC article

Molecular Phylogenies of Blastocystis Isolates From Different Hosts: Implications for Genetic Diversity, Identification of Species, and Zoonosis

Christophe Noël et al. J Clin Microbiol. .
Free PMC article


Small-subunit (SSU) rRNA gene sequences were obtained by PCR from 12 Blastocystis isolates from humans, rats, and reptiles for which elongation factor 1alpha (EF-1alpha) gene sequences are already available. These new sequences were analyzed by the Bayesian method in a broad phylogeny including, for the first time, all Blastocystis sequences available in the databases. Phylogenetic trees identified seven well-resolved groups plus several discrete lineages that could represent newly defined clades. Comparative analysis of SSU rRNA- and EF-1alpha-based trees obtained by maximum-likelihood methods from a restricted sampling (13 isolates) revealed overall agreement between the two phylogenies. In spite of their morphological similarity, sequence divergence among Blastocystis isolates reflected considerable genetic diversity that could be correlated with the existence of potentially >/=12 different species within the genus. Based on this analysis and previous PCR-based genotype classification data, six of these major groups might consist of Blastocystis isolates from both humans and other animal hosts, confirming the low host specificity of Blastocystis. Our results also strongly suggest the existence of numerous zoonotic isolates with frequent animal-to-human and human-to-animal transmissions and of a large potential reservoir in animals for infections in humans.


FIG. 1.
FIG. 1.
Maximum-likelihood phylogeny of Blastocystis isolates inferred from SSU rRNA gene sequences. P. lacertae served as the outgroup. Bayesian posterior probabilities are given as percentages near the individual nodes. Nodes with values of <50% are not shown. Blastocystis isolates from humans are indicated in boldface. Groups I to VII are those previously described by Arisue et al. (7), and the arrows indicate isolates for which classification is uncertain. Scale bar, 0.1 substitutions (corrected) per base pair.
FIG. 2.
FIG. 2.
Comparison of unrooted maximum-likelihood trees inferred from SSU rRNA (A) and EF-1α (B) sequences for the same sample of Blastocystis isolates. EF-1α nucleotide sequences are available in the GenBank database (accession numbers AF090737, AF091356 to AF091365, AF223379, and D64080). The numbers at the nodes correspond to Bayesian posterior probabilities given as percentages (left of the slash) and percentages of occurrence in 10,000 quartet puzzling steps (right of the slash). Asterisks designate nodes with values of <50%. Scale bars, 0.1 substitutions (corrected) per site.

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