Gut microbiota composition and function are major areas of research for functional gastrointestinal disorders. There is a connection between gastrointestinal tract and central nervous system and this is mediated by neurotransmitters, inflammatory cytokines, the vagus nerve and the hypothalamic-pituitary-adrenal axis. Functional gastrointestinal disorders are prevalent diseases affecting more than one third of the population. The etiology of these disorders is not clarified. Visceral hyperalgesia is the main hypothesis for explaining clinical symptoms, however gut-brain axis disorder is a new terminology for functional disorders. In this review, microbiota-gut-brain axis connection pathways and related disorders are discussed. Antibiotics are widely used in developed countries and recent evidence indicates antibiotic-induced dysbiosis as an important factor for functional disorders. Antibiotics exert negative effects on gut microbiota composition and functions. Antibiotic-induced dysbiosis is a major factor for occurrence of post-infectious irritable bowel syndrome. Cognitive and mood disorders are also frequent in functional gastrointestinal disorders. Animal and human trials show strong evidence for the causal relationship between gut microbiota and brain functions. Therapeutic implications of these newly defined pathogenic pathways are also discussed.

Background/Aims: It has been largely accepted that dietary habits affect intestinal microbiota composition. In this pilot study, we hypothesized that time-restricted feeding, which can be regarded as a type of intermittent fasting, may have a distinct effect on intestinal microbiota. Ramadan fasting is an excellent model to understand how time-restricted feeding affect the microbiota. Materials and Methods: A total of nine subjects were included in this study during Ramadan, consisting of 17 h of fasting/day during a 29-day period. Stool samples were collected at baseline and the day of the end of Ramadan. 16S rRNA qPCR assay has been performed for quantification of Akkermansia muciniphila, Faecalibacterium prausnitzii, Bifidobacterium spp., Lactobacillus spp., Bacteroides fragilis group, and Enterobacteriaceae. Blood samples were also collected to test for metabolic and nutritional parameters. Results: A significantly increased abundance of A. muciniphila and B. fragilis group was observed in all subjects after Islamic fasting when compared with the baseline levels (p=0.004 and 0.008, respectively). Serum fasting glucose and total cholesterol levels were also significantly reduced in all of the subjects (p<0.01 and p=0.009, respectively). Conclusion: Islamic fasting, which represents intermittent fasting, leads to an increase in A. muciniphila and B. fragilis group, which were considered as healthy gut microbiota members. Although this is a pilot study, which should be tested with larger sample size, there are a very limited number of studies in the literature on fasting and microbiota in human subjects. Thus, our present findings may contribute to the understanding of fasting-gut microbiota interaction.

It has been largely accepted that dietary changes have an effect on gut microbial composition. In this pilot study we hypothesised that Ramadan fasting, which can be considered as a type of time-restricted feeding may lead to changes in gut microbial composition and diversity. A total of 9 adult subjects were included in the study. Stool samples were collected before (baseline) and at the end of the Ramadan fasting (after 29 days). Following the construction of an 16S rRNA amplicon library, the V4 region was sequenced using the Illumina Miseq platform. Microbial community analysis was performed using the QIIME program. A total of 27,521 operational taxonomic units (OTUs) with a 97% similarity were determined in all of the samples. Microbial richness was significantly increased after Ramadan according to observed OTU results (P=0.016). No significant difference was found in terms of Shannon index or phylogenetic diversity metrics of alpha diversity. Microbial community structure was significantly different between baseline and after Ramadan samples according to unweighted UniFrac analysis (P=0.025). LEfSe analysis revealed that Butyricicoccus, Bacteroides, Faecalibacterium, Roseburia, Allobaculum, Eubacterium, Dialister and Erysipelotrichi were significantly enriched genera after the end of Ramadan fasting. According to random forest analysis, the bacterial species most affected by the Ramadan fasting was Butyricicoccus pullicaecorum. Despite this is a pilot study with a limited sample size; our results clearly revealed that Ramadan fasting, which represents an intermittent fasting regime, leads to compositional changes in the gut microbiota.

The gastrointestinal microbiota protects hosts from enteric infections; while antibiotics, by altering the microbiota, may diminish this protection. We show that after early-life exposure to antibiotics host susceptibility to enhanced Citrobacter rodentium -induced colitis is persistent and that this enhanced disease susceptibility is transferable by the antibiotic-altered microbiota. These results strongly suggest that early-life antibiotics have long-term consequences on the gut microbiota and enteropathogen infection susceptibility.

Background: There is increasing evidence that the intestinal microbiota plays a crucial role in the maturation of the immune system and the prevention of diseases during childhood. Early-life short-course antibiotic use may affect the progression of subsequent disease conditions by changing both host microbiota and immunologic development. Epidemiologic studies provide evidence that early-life antibiotic exposures predispose to inflammatory bowel disease (IBD). Methods: By using a murine model of dextran sodium sulfate (DSS)-induced colitis, we evaluated the effect on disease outcomes of early-life pulsed antibiotic treatment (PAT) using tylosin, a macrolide and amoxicillin, a beta-lactam. We evaluated microbiota effects at the 16S rRNA gene level, and intestinal T cells by flow cytometry. Antibiotic-perturbed or control microbiota were transferred to pups that then were challenged with DSS. Results: A single PAT course early-in-life exacerbated later DSS-induced colitis by both perturbing the microbial community and altering mucosal immune cell composition. By conventionalizing germ-free mice with either antibiotic-perturbed or control microbiota obtained 40 days after the challenge ended, we showed the transferrable and direct effect of the still-perturbed microbiota on colitis severity in the DSS model. Conclusions: The findings in this experimental model provide evidence that early-life microbiota perturbation may increase risk of colitis later in life.