Intestinal Bacterial Communities and Unicellular Parasites

Obesity is an epidemic causing a metabolic health crisis. Herein, the interactions between prokaryotic and eukaryotic intestinal communities were studied and correlated with metabolic comorbidities and diet. Stool samples from 56 subjects with grade II and III obesity were assessed for the richness, diversity and ecology of the bacterial gut community through metagenomics, together with the study of the presence of unicellular eukaryote parasites (Blastocystis sp., Dientamoeba fragilis and Giardia intestinalis) by qPCR. Clinical information regarding metabolic comorbidities and non-alcoholic hepatic fatty liver disease was gathered. To assess the quality of the patients' diet, each participant filled in three dietary questionnaires. The most prevalent parasite Blastocystis sp. (46.4%) together with D. fragilis (8.9%) correlated with a higher bacterial diversity regarding non-colonized subjects; the opposite of what was observed in those with G. intestinalis (16.1%). In terms of phyla relative abundance, with Blastocystis sp. and D. fragilis, very slight differences were observed; on the contrary, G. intestinalis was related to an increase in Bacteroidetes and Proteobacteria, and a decrease in Firmicutes and Actinobacteria, presenting the lowest Firmicutes/Bacteroidetes ratio. At genus level, Blastocystis sp. and/or D. fragilis was accompanied with an increase in Lactobacillus spp., and a decrease in Akkermansia spp., Bifidobacterium spp. and Escherichia spp., while G. intestinalis was associated with an increase in Bacteroides spp., and a decrease in Faecalibacterium spp., Prevotella spp. and Lactobacillus spp., and the highest Bacteroides spp./Prevotella spp. ratio. Participants with non-alcoholic hepatic fatty liver presented a higher Firmicutes/Bacteroidetes ratio, and those with type 2 diabetes displayed a significantly lower Faecalibacterium spp./Escherichia spp. ratio, due to an overrepresentation of the genus Escherichia spp. The presence of parasites is associated with variations in the richness, diversity and distribution of taxa in bacterial communities, confirming a gain in diversity associated with Blastocystis sp. and providing a different functioning of the microbiota with a positive effect on comorbidities such as type 2 diabetes, insulin resistance and metabolic syndrome. Future basic and clinical studies should assess the beneficial or pathogenic effect of these eukaryotes on obese subjects, and focus on deciphering whether they may imply a healthier metabolic profile.