The human gut microbiome is a dynamic ecosystem of microorganisms, influenced by numerous disparate factors including diet, age, and lifestyle. Investigating how changes in these variables affect the microbial gut community is limited due to the high variability found between individuals’ microbiota and limits inherent in sampling methodologies. Here we developed a microbial community with a defined species content - Lactocaseibacillus rhamnosus, Streptococcus salivarius, Enterococcus faecalis, and Bifidobacterium bifidum – mimicking the microbiota present in the small intestine. The biofilm community reached a steady state within 5–6 days of culture in a semi-batch system and once harvested and re-inoculated into a new reactor, the steady state was re-established within 24 hours. Biofilm development, microcolony structure, viability, and biomass were determined. Overall, this new “mock” community system can accurately mimic the small intestine microbiota and provide a platform to study community changes that occur due to environmental and chemical factors and lead to dysbiosis.

Consumed food travels through the gastrointestinal tract to reach the small intestine, where it interacts with the microbiota, forming a complex relationship with the dietary components. Here we present a complex in vitro cell culture model of the small intestine that includes human cells, digestion, a simulated meal, and a microbiota represented by a bacterial community consisting of E. coli, L. rhamnosus, S. salivarius, B. bifidum, and E. faecalis. This model was used to determine the effects of food-grade titanium dioxide nanoparticles (TiO2 NPs), a common food additive, on epithelial permeability, intestinal alkaline phosphatase activity, and nutrient transport across the epithelium. Physiologically relevant concentrations of TiO2 had no effect on intestinal permeability but caused an increase in triglyceride transport as part of the food model, which was reversed in the presence of bacteria. Individual bacterial species had no effect on glucose transport, but the bacterial community increased glucose transport, suggesting a change in bacterial behavior when in a community. Bacterial entrapment within the mucus layer was reduced with TiO2 exposure, which may be due to decreased mucus layer thickness. The combination of human cells, a synthetic meal, and a bacterial mock community provides an opportunity to understand the implications of nutritional changes on small intestinal function, including the microbiota.

Ingested dietary MgO-NPs could form different magnesium aggregates that would reach the small intestine and interact with the gut microbiota.