Genotypic Characterization of Blastocystis Isolates in the Philippines

Blastocystis is a common gut-dwelling protozoan found in animal and human hosts. Blastocystis organisms from nonhuman hosts are morphologically similar to Blastocystis hominis, hence, molecular characterization of this organism will contribute to the clearer understanding of its biology and transmission. In this study, a total of 274 stool samples from animal and human hosts were collected from farms, animal holding facilities, and public health institutions. One hundred samples (36.5%) were positive for Blastocystis by microscopy of fecal smear preparations. Restriction-fragment length polymorphism (RFLP) analysis of the small subunit ribosomal DNA (SSU rDNA) of 50 Blastocystis isolates revealed six different genotypes (ribodemes). Five Blastocystis genotypes (subtypes) were also identified by polymerase chain reaction (PCR) using sequence-tagged site (STS) primers. A certain degree of host specificity can be suggested for some strains of Blastocystis despite the genetic heterogeneity observed in the sampling population. The zoonotic property of Blastocystis was also observed in some of the isolates. This study contributes to the assessment of the extent of genetic variability of Blastocystis isolates in the Philippines and provides data that may support the zoonotic potential and host specificity of certain Blastocystis strains.