Construction of a model of the human proximal colon

Abstract

The objective of the present study was to construct a system that re-creates the conditions of fermentation and absorption of the human proximal colon. The model was constructed using a glass tube with an internal dialysis membrane tube. The food substrate was fed into the dialysis membrane three times a day simulating a typical human feeding. The substrate contained 58% carbohydrates, 35% proteins, 3% fiber, 3% starch, and 1% lipids on dry weight base, with 90% moisture. The inoculum was a fecal culture propagated in TSB. The intestinal absorption was simulated using a polyethylene glycol (PEG) solution running continuously outside the dialysis membrane. All microorganisms increased their counts after inoculation, and reached higher counts generally after substrate feed. The most important short chain fatty acids (SCFA: acetic, propionic and butyric acids) were analyzed, and their concentrations inside and outside the membrane were significantly different due to the extraction efficiency of the PEG solution. The greatest production occurred at 48 h. SCFA ratios showed that at the beginning, acetate was the predominant compound, but after 12 h the proportion of butyrate increased and the acetate was decreased. This SCFA production pattern is similar to that reported for the proximal colon in live systems. Continuous operation of the colon model for 48 h was enough to reveal the development of microorganisms and SCFA production. This model reproduced the conditions of the human proximal colon adequately and can be used to study the development of colonic microbiota.

Linking Microbial Community Structure to Function in Representative Simulated Systems

“…The total fatty acid content in the colon was insensitive to the presence or absence of the pathogen, although acetic acid levels decreased significantly (P Ͻ 0.05), while butyric acid levels increased significantly (P Ͻ 0.05), in the presence of E. coli O157:H7. Previous studies have suggested that microbial composition and fatty acid differences could be attributed to diet (15,(60)(61)(62)(63), pH (64), the peptide supply (64), and the relative amount of oxygen in the system (65,66). However, these parameters were consistent in this study, suggesting that the altered community structure is impacting the fatty acid composition of the model colon (64,67).…”

“…At the beginning of each week, the microbial community was taken from the stored glycerol stocks, inoculated into 200 ml colon medium (30), and placed in a shaker-incubator at 200 rpm and 37°C for 24 h. The bacterial suspension was then pumped into the dialysis tube of the model colon (Fig. 1, D) at a rate of 5 ml/min (Masterflex pump; Cole-Parmer, Vernon Hills, IL) (15) (Fig. 1, A).…”

“…The PEG mixture was fed into the area between the dialysis and the glass tubing in the model colon at a rate of 2.1 ml/min (Fig. 1, E), before the bacteria and the medium were allowed to flow into the model, and continuously until the end of the experiment, as described in previous research (15). To simulate typical adult feeding times, 100 ml of the colon medium mixture was pumped into the dialysis tube three times a day, 6 h apart, at a rate of 5 ml/min (15) (Fig.…”

“…In vitro systems, on the other hand, combine the complexity of environmental conditions with proper controls in the laboratory. Several in vitro models have been developed to simulate environments where pathogens may be found, including the guts of humans (15)(16)(17) and aquatic systems (18)(19)(20). These in vitro studies have allowed researchers to gain a better understanding of the behavior of microorganisms in environmentally relevant systems.…”

“…The function of in vitro gut environments has been tested by determining the microorganisms present (17,(21)(22)(23) and by monitoring fatty acid production (15,17,21,24) and enzymatic activity (17,21). For aquatic systems, such as surface water, wastewater, and groundwater, researchers have generally used synthetic formulas to recreate the aquatic chemistry found in those environments and to alleviate variability (18,(25)(26)(27)(28).…”