Objective The relevance of the microbe-gut-brain axis to psychopathology is of interest in anorexia nervosa (AN), as the intestinal microbiota plays a critical role in metabolic function and weight regulation. Methods We characterized the composition and diversity of the intestinal microbiota in AN, using stool samples collected at inpatient admission (T1; n = 16) and discharge (T2; n = 10). At T1, participants completed the Beck Depression and Anxiety Inventories and the Eating Disorder Examination–Questionnaire. Patients with AN were compared with healthy individuals who participated in a previous study (healthy comparison group; HCG). Genomic DNA was isolated from stool samples, and bacterial composition was characterized by 454 pyrosequencing of the 16S rRNA gene. Sequencing results were processed by the Quantitative Insights Into Microbial Ecology pipeline. We compared T1 versus T2 samples, samples from both points were compared with HCG (n = 12), and associations between psychopathology and T1 samples were explored. Results In patients with AN, significant changes emerged between T1 and T2 in taxa abundance and beta (between-sample) diversity. Patients with AN had significantly lower alpha (within-sample) diversity than did HCG at both T1 (p = .0001) and T2 (p = .016), and differences in taxa abundance were found between AN patients and HCG. Levels of depression, anxiety, and eating disorder psychopathology at T1 were associated with composition and diversity of the intestinal microbiota. Conclusions We provide evidence of an intestinal dysbiosis in AN and an association between mood and the enteric microbiota in this patient population. Future directions include mechanistic investigations of the microbe-gut-brain axis in animal models and association of microbial measures with metabolic changes and recovery indices.

Inflammatory bowel diseases (IBD) result from dysregulated immune responses toward microbial and perhaps other luminal antigens in a genetically susceptible host, and are associated with altered composition and diversity of the intestinal microbiota. The interleukin 10-deficient (IL-10−/−) mouse has been widely used to model human IBD; however the specific alterations that occur in the intestinal microbiota of this mouse model during the onset of colonic inflammation have not yet been defined. The aim of our study was to define the changes in diversity and composition that occur in the intestinal microbiota of IL-10−/− mice during the onset and progression of colonic inflammation. We used high throughput sequencing of the 16S rRNA gene to characterize the diversity and composition of formerly germ-free, wild-type and IL-10−/− mice associated with the same intestinal microbiota over time. Following two weeks of colonization with a specific pathogen-free (SPF) microbiota we observed a significant increase in the diversity and richness of the intestinal microbiota of wild-type mice. In contrast, a progressive decrease in diversity and richness was observed at three and four weeks in IL-10−/− mice. This decrease in diversity and richness was mirrored by an increase in Proteobacteria and Escherichia coli in IL-10−/− mice. An increase in E. coli was also observed in conventionally raised IL-10−/− mice at the point of colonic inflammation. Our data reports the sequential changes in diversity and composition of the intestinal microbiota in an immune-mediated mouse model that may help provide insights into the primary vs. secondary role of dysbiosis in human IBD patients.

Background: Recent studies have suggested a role for an altered intestinal microbiota in the pathophysiology of irritable bowel syndrome (IBS). However, no consensus has been reached regarding the association between specific enteric bacterial groups and IBS. The aim of this study was to investigate the fecal and mucosal-associated microbiota using two independent techniques in intestinal samples from diarrhea-predominant IBS (D-IBS) and healthy controls. Methods: Fecal and colonic mucosal biopsy samples were obtained from 10 D-IBS patients and 10 healthy controls. Colonic tissue was collected during a un-sedated un-prepped flexible sigmoidoscopy. Fecal and tissue samples were processed immediately upon collection for culture under aerobic and anaerobic conditions or frozen for further molecular analysis. DNA was extracted from all frozen samples and used to enumerate specific bacterial groups using quantitative real-time PCR (qPCR). Results: Culture analysis of intestinal samples demonstrated a significant reduction in the concentration of aerobic bacteria in fecal samples from D-IBS patients when compared to healthy controls (1.4 × 10⁷ vs. 8.4 × 10⁸ CFUs/g feces, P = 0.002). qPCR analysis demonstrated a significant 3.6 fold increase (P = 0.02) in concentrations of fecal Lactobacillus species between D-IBS patients and healthy controls. Conclusions: Our culture and molecular data indicate that quantitative differences exist in specific bacterial groups in the microbiota between D-IBS and healthy subjects.

Microbial protease-mediated disruption of the intestinal epithelium is a potential mechanism whereby a dysbiotic enteric microbiota can lead to disease. This mechanism was investigated using the colitogenic, protease-secreting enteric microbe Enterococcus faecalis . Caco-2 and T-84 epithelial cell monolayers and the mouse colonic epithelium were exposed to concentrated conditioned media (CCM) from E. faecalis V583 and E. faecalis lacking the gelatinase gene ( gelE ). The flux of fluorescein isothiocyanate (FITC)-labeled dextran across monolayers or the mouse epithelium following exposure to CCM from parental or mutant E. faecalis strains indicated paracellular permeability. A protease-activated receptor 2 (PAR2) antagonist and PAR2-deficient (PAR2 ^−/− ) mice were used to investigate the role of this receptor in E. faecalis -induced permeability. Gelatinase (GelE) purified from E. faecalis V583 was used to confirm the ability of this protease to induce epithelial cell permeability and activate PAR2. The protease-mediated permeability of colonic epithelia from wild-type (WT) and PAR2 ^−/− mice by fecal supernatants from ulcerative colitis patients was assessed. Secreted E. faecalis proteins induced permeability in epithelial cell monolayers, which was reduced in the absence of gelE or by blocking PAR2 activity. Secreted E. faecalis proteins induced permeability in the colonic epithelia of WT mice that was absent in tissues from PAR2 ^−/− mice. Purified GelE confirmed the ability of this protease to induce epithelial cell permeability via PAR2 activation. Fecal supernatants from ulcerative colitis patients induced permeability in the colonic epithelia of WT mice that was reduced in tissues from PAR2 ^−/− mice. Our investigations demonstrate that GelE from E. faecalis can regulate enteric epithelial permeability via PAR2.

This study examined associations between the composition and diversity of the intestinal microbiota and measures of depression, anxiety, eating disorder psychopathology, stress, and personality in a group of healthy adult females. Female participants (n = 91) ages 19–50 years with BMI 18.5–25 kg/m² were recruited from central North Carolina between July 2014 and March 2015. Participants provided a single fecal sample and completed an online psychiatric questionnaire that included five measures: (i) Beck Anxiety Inventory; (ii) Beck Depression Inventory-II; (iii) Eating Disorder Examination-Questionnaire; (iv) Perceived Stress Scale; and (v) Mini International Personality Item Pool. Bacterial composition and diversity were characterized by Illumina sequencing of the 16S rRNA gene, and associations were examined using Kendall’s tau-b correlation coefficient, in conjunction with Benjamini and Hochberg’s False Discovery Rate procedure. We found no significant associations between microbial markers of gut composition and diversity and scores on psychiatric measures of anxiety, depression, eating-related thoughts and behaviors, stress, or personality in a large cohort of healthy adult females. This study was the first specifically to examine associations between the intestinal microbiota and psychiatric measures in healthy females, and based on 16S rRNA taxonomic abundances and diversity measures, our results do not suggest a strong role for the enteric microbe-gut-brain axis in normal variation on responses to psychiatric measures in this population. However, the role of the intestinal microbiota in the pathophysiology of psychiatric illness may be limited to more severe psychopathology.