Comparison of sequencing (barcode region) and sequence-tagged-site PCR for Blastocystis subtyping.

Blastocystis is the most common nonfungal microeukaryote of the human intestinal tract and comprises numerous subtypes (STs), nine of which have been found in humans (ST1 to ST9). While efforts continue to explore the relationship between human health status and subtypes, no consensus regarding subtyping methodology exists. It has been speculated that differences detected in subtype distribution in various cohorts may to some extent reflect different approaches. Blastocystis subtypes have been determined primarily in one of two ways: (i) sequencing of small subunit rRNA gene (SSU-rDNA) PCR products and (ii) PCR with subtype-specific sequence-tagged-site (STS) diagnostic primers. Here, STS primers were evaluated against a panel of samples (n = 58) already subtyped by SSU-rDNA sequencing (barcode region), including subtypes for which STS primers are not available, and a small panel of DNAs from four other eukaryotes often present in feces (n = 18). Although the STS primers appeared to be highly specific, their sensitivity was only moderate, and the results indicated that some infections may go undetected when this method is used. False-negative STS results were not linked exclusively to certain subtypes or alleles, and evidence of substantial genetic variation in STS loci was obtained. Since the majority of DNAs included here were extracted from feces, it is possible that STS primers may generally work better with DNAs extracted from Blastocystis cultures. In conclusion, due to its higher applicability and sensitivity, and since sequence information is useful for other forms of research, SSU-rDNA barcoding is recommended as the method of choice for Blastocystis subtyping.