Subtype Distribution of Blastocystis spp. with DNA Barcoding and Evaluation of Diagnostic Methods

Abstract

Blastocystis spp. is one of the most common protozoa in Turkey and throughout the world; laboratory diagnosis, genetic diversity and clinical features are among the most controversial topics related to the parasite. The aims of the present study were to investigate the subtype distribution of Blastocystis spp. İsolates from Aydin, Turkey, to evaluate the efficiency of some diagnostic methods and to evaluate the relationship between Blastocystis spp. infection with demographic factors and clinical findings. According to the direct microscopy results, 100 stool samples with and without Blastocystis spp. were selected by simple random sampling method. All were directly subjected to DNA isolation and cultured in Jones medium. DNA isolation was also carried out in Blastocystis spp. positive cultures with a different kit. Genomic DNA samples were analysed by PCR targeting the Blastocystis spp. small subunit ribosomal RNA (SSU rRNA) gene and subtypes (ST) were determined according to the sequence analyses. Moreover, the samples with undetected ST were further studied with sequence tagged site-PCR (STS-PCR). In addition, the patients with and without Blastocystis spp. were compared in terms of demographic characteristics (gender, age, residence) and clinical findings (itching, diarrhoea, abdominal pain, dyspepsia, nausea, vomiting, constipation and weight loss)., Among 100 stool positive samples diagnosed with direct microscopic examination 81 (81%) and 86 (86%) were found as positive with culture and PCR, retrospectively. Additionally, among 100 Blastocystis spp. negative stool samples five (5%) and seven (7%) samples were found positive with the same methods, respectively. The results of the analysis of Blastocystis spp. with SSU rRNA gene sequencing and STS-PCR methods revealed the subtype distribution of 95 Blastocystis spp. isolates as follows: ST3 (n= 50, 52.6%), ST2 (n= 21, 22.1%), ST1 (n= 17, 17.9%), ST7 (n= 4, 4.2%), ST2 + ST3 (n= 2, 2.1%) and ST1 + ST3 (n= 1, 1.1%). In addition, a complete accordance was observed in subtype distribution between direct DNA isolation from stools and 35 randomly selected isolates from the culture. In our study, the comparison of 107 Blastocystis spp. positive (by any of the methods) cases and 93 negative cases showed that there was no correlation in terms of demographic characteristics and clinical findings. Similarly, there was no significant relationship between symptoms and subtypes. In conclusion, it is recommended that in addition to direct microscopic examination, the use of additional methods such as culture and PCR will be useful in routine laboratory diagnosis of Blastocystis spp. The distribution of Blastocystis subtype in Aydin is mainly in accordance with the global findings. Lack of a relationship between Blastocystis spp. İnfection and symptoms in our study was supported the idea that Blastocystis spp. infection is mostly asymptomatic in humans and it may be a member of healthy microbiota.