Exploring the microbiota of the gastrointestinal tract

University dissertation from Media-Tryck

Abstract: Abstract: Balanced microbiota of the gastrointestinal (GI) tract is important for maintaining health of the host. Altered gut microbiota have been found to be associated with various life-style induced and other intestinal inflammatory diseases. Gut microbiota is viewed as a metabolic organ and considered as new target for therapies. This thesis describes the work on exploring the microbiota of the GI tract under different conditions. Under the functional food concept, probiotics, prebiotics, food component with prebiotic potientials were used as means to modulate the microbiota of the GI tract. Murine models are commonly used to study the role of the microbiota. However, difference in genetic backgrounds, husbandry conditions may affect the microbiota composition and contribute to the different outcomes of a dietary intervention. We observed that two substrains of C57BL/6 mice fed the same diet harbored different microbiota. In agreement with other studies, this indicates that not only diet but other environmental factors are involved in shaping the gut microbiota. We have investigated the impact of high fat diet on the microbiota and tested multiple functional foods with the aim of improving the host health conditions. We found that high fat diet reshaped the gut microbiota using a mouse model. For example, Allobaculum-like bacteria was decreasing whereas Akkermansia-like bacteria were increasing with high fat feeding in C57BL/6 mice. Supplementations of green tea and Lactobacillus plantarum HEAL19 attenuated high fat-induced inflammation and altered the gut microbiota composition. Combining the L. plantarum HEAL19 with different doses of green tea resulted in a gradient shift in the microbiota and different impact on certain bacterial species. Addition of the dietary fibers i.e. pectin or guar gum shifted the gut microbiota differently. Pectin fed rats had significant reduction in weight gain and had increased abundance of Lachnospiraceae and an unidentified bacterial group. Berries alone or with probiotics were tested under different host health conditions including healthy, hypertensive and inflammatory state. In murine models, raspberry increased bacterial diversity in the microbiota of rats when compared to blackcurrant. The addition of the L. plantarum HEAL19 to the berries did not induce profound effect on the gut microbiota. Fermented bilberries by the L. plantraum HEAL19 showed blood pressure lowering effect in healthy and L-NAME-induced hypertensive rats and altered the gut microbiota composition. Supplementation of bilberries protected against inflammation and oxidative stress in an ischemia−reperfusion-mice model and altered cecal microbiota. The addition of probiotics did not have a profound effect on either the health improvement or gut microbiota composition. Three-month intake of dietary supplements containing either L. plantarum HEAL19 or L. plantarum HEAL19 plus fermented bilberries did not have an obvious impact on the oral and fecal microbiota of hypertensive research persons. Both the oral and the fecal microbiota were relatively stable and the two most fluctuating bacterial taxa in the fecal microbiota were Bacteroides and unclassified Rikenellaceae. In a dextran sodium sulfate (DSS)-induced colitis mouse model, colonic mucosa associated microbiota were different from the healthy controls. Total load of bacteria and the amount of Akkermansia and Desulfovibrio were significantly higher in the mice with colitis than the healty controls. In contrast Lactobacillus was significantly reduced in colitis group. Moreover, the prevelence of Enterobacteraiceae was significantly higher in the colitis group. Ileal pouch microbiota of former patients with ulcerative colitis one year after surgery was colonized predominantly with Fimicutes at phylum level. The most abundant genera during the first year after surgery were found to be Clostridium, Blautia, Roseburia, Lachnospira, unclassified Lachnospiraceae, Bacteroides, Faecalibacterium, unclassified Petostreptococcaceae and Megamonas. In conclusion, diet and other environmental factors are involved in shaping the microbiota of the GI tract. Different diet components have different influence on the microbiota composition. In general, the intestinal Bacteroidales taxa were the most active responders for the diet treatments.