Preliminary molecular characterization of Blastocystis sp. subtypes among IBS patients and non-IBS individuals in Hamadan Province, western Iran

Blastocystis sp. is a common protozoan parasite in humans and has frequently been implicated in gastrointestinal disorders such as irritable bowel syndrome (IBS). This study aimed to preliminarily characterize and descriptively compare the distribution of Blastocystis subtypes among IBS patients and non-IBS individuals. Eighty stool samples positive for Blastocystis sp. were collected, comprising 40 samples from patients with IBS and 40 samples from non-IBS individuals in Hamadan Province, western Iran. Each sample was examined using microscopic and culture techniques to confirm Blastocystis sp. polymerase chain reaction (PCR) was performed to amplify a specific region of the small subunit ribosomal RNA (SSU rRNA) gene. Of the 80 PCR-positive samples, 28 (14 from each group) yielded sequences suitable for subtype determination. Sequencing and phylogenetic analyses were performed to identify subtypes using the ClustalW algorithm, MEGA and DnaSP software. Of the 80 Blastocystis -positive samples, 28 were successfully sequenced, including 14 samples from the IBS group and 14 from the non-IBS group (14 per group), and three distinct subtypes were identified: ST1, ST2, and ST3. Among the 14 successfully sequenced IBS samples, ST3 was detected in 12 (85.7%) and ST1 in 2 (14.3%). Among the 14 successfully sequenced non-IBS samples, ST1 was detected in 10 (71.4%) and ST2 in 4 (28.6%). Among the successfully sequenced isolates, ST3 was predominant in IBS patients, whereas ST1 was predominant in non-IBS individuals. Given the limited number of successfully sequenced samples, these findings should be considered preliminary and hypothesis generating rather than representative of the broader population.