Direct detection of Blastocystis sp. in human faecal samples and subtype assignment using single strand conformational polymorphism and sequencing.

Blastocystis is an anaerobic parasitic microorganism, which has been found in the intestinal tract of many vertebrates including humans. Recently, members of Blastocystis sp. were classified into nine subtypes, based on phylogenetic trees derived from sequence analysis of the small subunit ribosomal RNA (SSU rRNA) gene. The role of Blastocystis in human disease remains uncertain and the existence of pathogenic and non-pathogenic subtypes is under investigation. We report the development of a polymerase chain reaction (PCR)-based assay that is able to detect Blastocystis directly from human faeces. Furthermore, combined with single strand conformational polymorphism (SSCP) analysis and/or sequencing of the respective PCR product, the protocol can classify Blastocystis among the nine established subtypes. The method was applied to 45-positive and 30-negative faecal samples and proved to be highly sensitive and specific. Genotyping using SSCP analysis and sequencing revealed that subtype 3 is the most frequent in Greece, while subtypes 1, 2, 4, 6 and 7 are also present but in lower frequencies. Hopefully, the simplicity of the proposed method will contribute toward large-scale epidemiological studies for prompt clarification of the role of the parasite.