Genetic diversity analysis of Blastocystis subtypes from both symptomatic and asymptomatic subjects using a barcoding region from the 18S rRNA gene.

Blastocystis is the most prevalent protozoa found in human stool samples. This study aimed to evaluate genetic diversity among Blastocystis subtypes isolated from both symptomatic and asymptomatic subjects as well as the potential correlation between subtypes and symptoms. A total of 55 Blastocystis-positive isolates were included in this study. A barcoding region of the small subunit rDNA was amplified and genetically assessed using MEGA6 and DnaSP regarding the presence of symptoms. BLAST analyses revealed the presence of 5 different subtypes (ST1, ST2, ST3, ST6 and ST7) among the samples. ST3 was the most prevalent subtype (25/55, 45%) while only one ST7 isolate was detected. Moreover, alleles 4 and 86 for ST1; alleles 9, 11 and 12 for ST2; alleles 31, 34, 36, 37 and 52 for ST3; allele 122 for ST6 and allele 137 for ST7 were detected. No statistically significant association was found between gender and symptoms with certain subtypes. Analysis of the intra-subtype variability in both symptomatic and asymptomatic subjects revealed highest similarity among ST1 isolates while lowest similarity was seen among ST3 isolates. Neutrality indices, Tajima's D and Fu's Fs, were negative but only statistically significant for ST3. Furthermore, highest values of Hd, π and S were observed among ST1, ST2 and ST3 isolated from symptomatic patients indicating high level of diversity among isolates obtained from these subjects. In addition, inter-subtype analysis showed the highest similarity between ST1 and ST2 isolates and the lowest similarity between ST2 and ST7 isolates. This is the first study revealing the presence of both ST6 and ST7 isolates in human from Iran. Phylogenetic analysis did not suggest any significant correlation between clinical manifestations and certain subtypes although genetic analysis showed highest value of diversity and significant neutrality indices among ST3 isolates obtained from symptomatic patients.