Molecular identification and genotyping of Blastocystis spp. in children with clinical symptoms in southeast Iran using PCR-sequencing method

Blastocystis spp. is a zoonotic anaerobic parasite that has been identified in the large intestine of humans and many vertebrates. It is predominantly encountered in individuals with frequent contact with animals. The present study aims to identify the prevalence of Blastocystis spp. and its common genotypes in children with clinical symptoms of diarrhea in the city of Zahedan, located in the southeast of Iran. A cross-sectional descriptive study was conducted on 60 children under ten years of age with gastrointestinal symptoms, especially diarrhea. Following the collection of samples, stool samples were subjected to direct stool testing for the initial diagnosis. Following this, a microscopic diagnosis was made, after which DNA was extracted and a Polymerase Chain Reaction (PCR) test with a small subunit ribosomal RNA (SSU rRNA) gene target was performed. The PCR products were then purified and sequenced. The resulting nucleotide sequences were then subjected to a thorough review using Chromas biotechnology software version 2.4 and CLC genomic work bench software 11. The alignment of the nucleotide sequences was subsequently facilitated by utilizing the BLAST database, and these sequences were then compared with the reference genotypes of Blastocystis spp. that are stored within the gene bank. The genotyping of the sequences was conducted using CLC genomic work bench software 11, and a phylogenetic tree was constructed using MEGA7 software with the Neighbor-Joining statistical method, which applied the Kimura 2-parameter method. Out of the 60 cases that were examined, 5 children (8.33%) were found to be positive by direct microscopic and PCR tests, where a 500 (479) bp fragment in the SSU-rRNA target was detected. Subsequent genetic analysis identified four distinct subtypes, including subtypes 1, 2, 3, and 5. The percentage of nucleotide identity with the sequences in the gene bank was found to be between 93 and 100%. Given the presence of subtypes 3 and 5 in the study and the evidence of their zoonotic nature, it can be concluded that examining parasite dynamics and epidemiological principles can be effective in the control strategy.