Blastocystis isolates from a pig and a horse are closely related to Blastocystis hominis

Abstract

Blastocystis has a widespread distribution in a variety of animals, which is a potential source of infection for humans. However, the contribution of zoonotic transmission remains unclear due to the absence of molecular proof of these organisms being identical to those found in humans. We report herein the similar subgroup of Blastocystis isolates from humans, pigs, and a horse using a restriction fragment length polymorphism (RFLP) analysis of partial small-subunit ribosomal DNA (ssu rDNA). Additionally, sequence and phylogenic analysis of partial ssu rDNA of Blastocystis from a human, a pig, and a horse sharing a common subgroup shows that Blastocystis isolates from a pig and a horse were monophyletic and closely related to B. hominis, with 92 to 94% identity. These results suggest the possibility of zoonotic potential of Blastocystis.

FIG. 1.

Comparison of the representative PCR-RFLP analysis of partial ssu rDNA of Blastocystis isolates from a human (lanes 1 to 3), a pig (lanes 4 to 6), and a horse (lanes 7 to 9). These banding patterns were identified as subgroup III as previously described (3). The PCR product in lanes 1, 4, and 7 was digested by HinfI; the PCR product in lanes 2, 5, and 8 was digested by RsaI; and the PCR product in lane 3, 6, and 9 was digested with AluI. MW, molecular weight marker.

FIG. 2.

Banding patterns of subgroup I (A) and subgroup VI (B) using PCR-RFLP analysis of partial ssu rDNA of Blastocystis isolated from humans. The PCR product in lane 1 was digested by HinfI, the PCR product in lane 2 was digested by RsaI, and the PCR product in lane 3 was digested by AluI. MW, molecular weight marker.

FIG. 3.

Phylogenetic relationships of selected Blastocystis spp. inferred from partial ssu rDNA sequence (1,054 bp). A single most-parsimonious tree with tree length of 355, consistency index of 0.9352, and retention index of 0.8663 was found. Bootstrap replicates, 1,000. Bootstrap frequencies of more than 50 are indicated on each branch. GenBank accession numbers of sequences are in parentheses.

FIG. 4.

Maximum analysis of ssu rDNA sequences of 1,054 bp for selected genera in Blastocystis and Caecitellus parvulus as a reference taxon. GenBank accession numbers and hosts of each taxon are in parentheses.

FIG. 5.

Neighbor-joining based on ssu rDNA analysis containing 9 taxa of selected genera in Blastocystis. The designated outgroup is Caecitellus parvulus. GenBank accession numbers and hosts of each taxon are in parentheses.

FIG. 6.

Phylogenetic relationships of selected Blastocystis spp. inferred from partial ssu rDNA sequence (1,738 bp). A single most-parsimonious tree with tree length of 520, consistency index of 0.9577, and retention index of 0. 9185 is shown. Bootstrap replicates, 1,000. Bootstrap frequencies of more than 50 are indicated on each branch. Nodes and clades are numbered in parentheses in the order in which they are described in the text. Bar, 10 substitutions. GenBank accession numbers of sequences are in parentheses.