In vitro assessment of the effect of commercial botanical products on the human fecal bacterial community structure
The surging popularity of botanical extracts in dietary supplements has prompted a closer examination of their potential impact on the gut microbiota. Despite historical research predominantly focusing on prebiotic activity, these extracts harbour compounds with broad-spectrum antimicrobial activity. This study aims to assess the impact of three commercially available plant-based food supplement ingredients (Bromeyal®, Axtragyl®, and Kalita® derived from pineapple, Astragalus membranaceus roots, and bergamot, respectively), owned by Giellepi SpA, on the human gut microbiome through an in vitro fecal incubation model and on single selected bacterial strains.  Testing involved three concentrations of the three products post in vitro digestion, adhering to the INFOGEST protocol, or in their original form. A microbiologically stable fecal suspension, emulating an active microbiota, was prepared using glycerol-supplemented fecal samples and stored at -80°C. Assessments included fecal suspension incubations in anaerobic conditions with the products.  Metataxonomic analysis by 16S rRNA gene amplicon profiling enabled comprehension of bacterial diversity and abundance in the samples. Cultivation of selected individual bacterial strains (e.g., Bifidobacterium spp., Bacteroides fragilis, and Odoribacter splanchnicus) in the presence of the products was also performed.  The three products exhibited no adverse impact on the fecal suspension microbiota, maintaining stability in a-diversity, ß-diversity, and most major bacterial taxa during incubations, while some species, genera, and bacterial families displayed moderate alterations. The cultivation of most single strains in the presence of the products revealed no significant differences in viable counts compared to the control, even at concentrations surpassing those realistically achievable through product consumption.  This study pioneers the assessment of gut microbiome harmlessness of specific commercial botanical products. Findings demonstrate minimal influence on the fecal microbiota structure, with partial inhibition of groups linked to potential negative health impacts and partial promotion of health-enhancing bacteria.  In conclusion, the tested food supplements ingredients, despite containing molecules with documented antimicrobial activity, can showcase a positive impact on health without disrupting the equilibrium of the human intestinal microbiota, rendering them microbiome-friendly.