Blastocystis in the faeces of children from six distant countries: prevalence, quantity, subtypes and the relation to the gut bacteriome.

BACKGROUND Blastocystis is a human gut symbiont of yet undefined clinical significance. In a set of faecal samples collected from asymptomatic children of six distant populations, we first assessed the community profiles of protist 18S rDNA and then characterized Blastocystis subtypes and tested Blastocystis association with the faecal bacteriome community. METHODS Stool samples were collected from 244 children and young persons (mean age 11.3 years, interquartile range 8.1-13.7) of six countries (Azerbaijan 51 subjects, Czechia 52, Jordan 40, Nigeria 27, Sudan 59 and Tanzania 15). The subjects showed no symptoms of infection. Amplicon profiling of the 18S rDNA was used for verification that Blastocystis was the most frequent protist, whereas specific real-time PCR showed its prevalence and quantity, and massive parallel amplicon sequencing defined the Blastocystis subtypes. The relation between Blastocystis and the stool bacteriome community was characterized using 16S rDNA profiling. RESULTS Blastocystis was detected by specific PCR in 36% (88/244) stool samples and was the most often observed faecal protist. Children from Czechia and Jordan had significantly lower prevalence than children from the remaining countries. The most frequent subtype was ST3 (49%, 40/81 sequenced samples), followed by ST1 (36%) and ST2 (25%). Co-infection with two different subtypes was noted in 12% samples. The faecal bacteriome had higher richness in Blastocystis-positive samples, and Blastocystis was associated with significantly different community composition regardless of the country (p < 0.001 in constrained redundancy analysis). Several taxa differed with Blastocystis positivity or quantity: two genera of Ruminococcaceae were more abundant, while Bifidobacterium, Veillonella, Lactobacillus and several other genera were undrerrepresented. CONCLUSIONS Asymptomatic children frequently carry Blastocystis, and co-infection with multiple distinct subtypes is not exceptional. Prevalence and quantity of the organism clearly differ among populations. Blastocystis is linked to both faecal bacteriome diversity and its composition.