Influence of viscosity on the growth of human gut microbiota

Numerous studies support the beneficial effects of dietary fibre. It is well known that fibre increases viscosity at intestinal level. Therefore, the effects of fibre on gut microbiota could be due not only by its intestinal bacteria fermentation but also to the increase in viscosity by itself. The aim of this study was to evaluate the effect of viscosity on the growth of gut microbiota at physiological conditions. For this purpose, four compartments from a gastrointestinal simulator (simgi (R)) were filled with Gut Nutrient Medium (GNM) plus different agar concentrations (0, 0.30, 0.45 and 0.60%), inoculated with faecal microbiota, and incubated 48 h under anaerobic conditions. Samples were collected at three time points (0, 24 h and 48 h) for representative intestinal bacterial enumeration and rheological characterization. Incubation of GNM gels with faecal microbiota changed the medium viscosity over time, even with constant conditions (temperature and pH). In such way that, in absence of agar (low viscosity), viscosity slightly increased over time; however, in viscous mediums, viscosity decreased over time. In relation to the growth of gut microbiota, results showed that viscosity favoured the growth of total anaerobes and Clostridium spp.; in contrast, total number of aerobes and members of the genus Enterococcus correlated negatively with viscosity increment. In conclusion, changes in intestinal viscosity seem to selectively modify microbiota composition. This is a pioneer work to understand the effect of food viscosity in the gastrointestinal system, showing that viscosity is an important factor itself to condition the growth of different bacteria's groups. (C) 2017 Elsevier Ltd. All rights reserved.