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OBJECTIVES: The human small intestine is a complex and dynamic organ tasked with enzymatic digestion and absorption of nutrients. Design of a small intestine model can provide detailed systematic knowledge of these processes; model design challenges include differential pH and oxygen availability along the length of the small intestine, food-dependent host secretion of digestive compounds, complex nutrient absorption processes, and microbiome interactions with both food and host. Numerous in vitro models have been developed to simulate the small intestine, but physiological relevance is limited. Here, we present an in vitro fermentation model of the small intestine to include microbiota and enhance physiological relevance. METHODS: A stepwise biofidelic model design approach was implemented with initial stages consisting of simulating ileum conditions, including pH and residence time, utilizing an automated bioreactor system for real-time monitoring and control of fermentation parameters, with incorporation of digestive enzymes and bile acids for breakdown of food inputs. Nutrient absorption, simulated using hollow-fiber columns to emulate passive diffusion, was initially optimized using small molecules to mimic dietary digestion byproducts; validation with food components, such as starch or whey powder, is planned. A mock microbial community, with organisms selected to represent major phyla and functions of the small intestine microbiota, was designed, implemented, and characterized in fermentations representing “fed-state” ileum conditions. RESULTS: Design and validation of the model with mock food components will be presented, along with steps taken to integrate in situ nutrient absorption and mock microbial community. Initial characterization of the microbial community indicates synergistic growth dynamics and nutrient utilization under “fed-state” conditions. CONCLUSIONS: These efforts will be the foundation for our long-term goal of simulating the small intestine to complement our large intestine fermentation model, jA(2)COB, creating a complete in vitro fermentation model of the lower GI tract. Insight gleaned from this model, alone or in concert with in vivo studies, can inform nutritional strategies to restore and maintain host gut homeostasis. FUNDING SOURCES: Funded by U.S. Army NSRDEC core applied research funds.

OBJECTIVES: From a military perspective, the gut microbiome serves as an ideal tool to enhance Soldier gut and immune health and to improve survivability and performance. Our work employs in vitro tools as a means to elucidate systematic processes of colonic bacterial metabolism of dietary inputs under native and stressed conditions. This talk will focus on the use of in vitro fermentation to investigate both the prebiotic potential of cranberry proanthocyanidins (PAC) within a healthy microbiome and stress-induced alterations in microbial inter-species competition for fermentable fiber. METHODS: Fermentations were performed in triplicate, utilizing fecal inocula derived from at least three individuals, in a nutrient-rich anaerobic medium with sampling at 0 and 24 hrs. Within PAC supplementation studies, samples were analyzed for bacterial identification (16 s rRNA sequencing) and metabolite content (GC-FID and GC/MS). Stressed metabolism studies, which utilized fecal samples before and after a 21-day change in diet challenge (habitual vs. Meal Ready-to-Eat), employed media supplemented with resistant starch under ascending colon domain-specific conditions; samples taken were analyzed for bacterial identification (16 s rRNA) and enumeration of select organisms (qPCR). RESULTS: Bacterial population dynamics within PAC supplementation studies indicated a dose-dependent increase in several beneficial taxa, including Ruminococcus spp (P