Schematic representation of the TNO TIM-2 in vitro model with (a) peristaltic compartments containing fecal matter; (b) pH electrode; (c) alkali pump; (d) dialysis liquid circuit with hollow fibre membrane; (e) level sensor; (f) N
gas inlet; (g) sampling port; (h) gas outlet; (i) 'ileal efflux' container containing SIEM; (j) temperature sensor. In brief, the model consists of four glass units with a flexible wall inside (peristaltic compartments) and a total volume of 135 ml. Water of body temperature (37°C) was pumped into the space between the glass jacket and the flexible wall, causing the microbiota to be mixed and moved. The sequential squeezing of the walls, controlled by a computer, caused a peristaltic wave forcing the material to circulate through the loop-shaped system. Physiological electrolyte and metabolite concentrations in the lumen were maintained with a dialysis system consisting of hollow fibres, running through the lumen of the reactor, through which dialysis liquid was pumped at a speed of 1.5 ml/min. The model further contained an inlet system for delivery of the artificial ileal delivery medium (SIEM), and a level sensor to maintain the luminal content at the set level of 135 ml. The system was kept anaerobic by flushing with gaseous nitrogen. At the start of each experiment the model was inoculated with 30 ml of the standard, cultivated faecal microbiota, consisting of a mix of fecal samples from 7 individuals. The composition of this microbiota consisted of all microbes present in the fecal donations (unpublished data).