Kashyap, Purna

SummaryBackgroundClostridium difficile infection (CDI) may not respond to initial therapy and frequently recurs, but predictors of response and recurrence are inconsistent. The impact of specific alterations in the gut microbiota determining treatment response and recurrence in patients with CDI is unknown.AimTo assess microbial signatures as predictors of treatment response and recurrence in CDI.MethodsPre‐treatment stool samples and clinical metadata including outcomes were collected prospectively from patients with their first CDI episode. Next generation 16s rRNA sequencing using MiSeq Illumina platform was performed and changes in microbial community structure were correlated with CDI outcomes.ResultsEighty‐eight patients (median age 52.7 years, 60.2% female) were included. Treatment failure occurred in 12.5% and recurrence after response in 28.5%. Patients who responded to treatment had an increase in Ruminococcaceae, Rikenellaceae, Clostridiaceae, Bacteroides, Faecalibacterium and Rothia compared to nonresponders. A risk‐index built from this panel of microbes differentiated responders (mean 0.07 ± 0.24) from nonresponders (0.52 ± 0.42; P = 0.0002). Receiver operating characteristic (ROC) curve demonstrated that risk‐index was a strong predictor of treatment response with an area under the curve (AUC) of 0.85. Among clinical parameters tested, only proton pump inhibitor use predicted recurrent CDI (OR 3.75, 95% CI 1.27–11.1, P = 0.01). Patients with recurrent CDI had statistically significant increases in Veillonella, Enterobacteriaceae, Streptococci, Parabacteroides and Lachnospiraceae compared to patients without recurrence and a risk index was able to predict recurrence (AUC = 0.78).ConclusionGut microbiota signatures predict treatment response and recurrence potentially, allowing identification of patients with Clostridium difficile infection that may benefit from early institution of alternate therapies.

SummaryBackgroundInfectious enteritis is a commonly identified risk factor for irritable bowel syndrome (IBS). The incidence of Clostridium difficile infection (CDI) is on the rise. However, there is limited information on post‐infectious IBS (PI‐IBS) development following CDI and the host‐ and infection‐related risk factors are not known.AimTo determine the incidence and risk factors for PI‐IBS following CDI.MethodsA total of 684 cases of CDI identified from September 2012 to November 2013 were surveyed. Participants completed the Rome III IBS questionnaire and details on the CDI episode. Predictive modelling was done using logistic regression to evaluate risk factors for PI‐IBS development.ResultsA total of 315 CDI cases responded (46% response rate) and 205 were at‐risk (no pre‐CDI IBS) for PI‐IBS development. A total of 52/205 (25%) met the Rome III criteria for IBS ≥6 months following CDI. IBS‐mixed was most common followed by IBS‐diarrhoea. In comparison to those without subsequent PI‐IBS, greater percentage of PI‐IBS patients had CDI symptoms >7 days, nausea, vomiting, abdominal pain during CDI, anxiety and a higher BMI. Using logistic regression, CDI symptoms >7 days [Odds ratio (OR): 2.96, P = 0.01], current anxiety (OR: 1.33, P < 0.0001) and a higher BMI (OR: 1.08, P = 0.004) were independently associated with PI‐IBS development; blood in the stool during CDI was protective (OR: 0.44, P = 0.06).ConclusionsIn this cohort study, new‐onset IBS is common after CDI. Longer CDI duration, current anxiety and higher BMI are associated with the diagnosis of C. difficile PI‐IBS. This chronic sequela should be considered during active management and follow‐up of patients with CDI.

Key pointsThe gastrointestinal epithelial enterochromaffin (EC) cell synthesizes the vast majority of the body's serotonin. As a specialized mechanosensor, the EC cell releases this serotonin in response to mechanical forces. However, the molecular mechanism of EC cell mechanotransduction is unknown.In the present study, we show, for the first time, that the mechanosensitive ion channel Piezo2 is specifically expressed by the human and mouse EC cells.Activation of Piezo2 by mechanical forces results in a characteristic ionic current, the release of serotonin and stimulation of gastrointestinal secretion.Piezo2 inhibition by drugs or molecular knockdown decreases mechanosensitive currents, serotonin release and downstream physiological effects.The results of the present study suggest that the mechanosensitive ion channel Piezo2 is specifically expressed by the EC cells of the human and mouse small bowel and that it is important for EC cell mechanotransduction.AbstractThe enterochromaffin (EC) cell in the gastrointestinal (GI) epithelium is the source of nearly all systemic serotonin (5‐hydroxytryptamine; 5‐HT), which is an important neurotransmitter and endocrine, autocrine and paracrine hormone. The EC cell is a specialized mechanosensor, and it is well known that it releases 5‐HT in response to mechanical forces. However, the EC cell mechanotransduction mechanism is unknown. The present study aimed to determine whether Piezo2 is involved in EC cell mechanosensation. Piezo2 mRNA was expressed in human jejunum and mouse mucosa from all segments of the small bowel. Piezo2 immunoreactivity localized specifically within EC cells of human and mouse small bowel epithelium. The EC cell model released 5‐HT in response to stretch, and had Piezo2 mRNA and protein, as well as a mechanically‐sensitive inward non‐selective cation current characteristic of Piezo2. Both inward currents and 5‐HT release were inhibited by Piezo2 small interfering RNA and antagonists (Gd3+and D‐GsMTx4). Jejunum mucosal pressure increased 5‐HT release and short‐circuit current via submucosal 5‐HT3 and 5‐HT4 receptors. Pressure‐induced secretion was inhibited by the mechanosensitive ion channel antagonists gadolinium, ruthenium red and D‐GsMTx4. We conclude that the EC cells in the human and mouse small bowel GI epithelium selectively express the mechanosensitive ion channel Piezo2, and also that activation of Piezo2 by force leads to inward currents, 5‐HT release and an increase in mucosal secretion. Therefore, Piezo2 is critical to EC cell mechanosensitivity and downstream physiological effects.

Aryl hydrocarbon receptor ligands from bacterial metabolism of tryptophan can mitigate inflammation in the gut and central nervous system.

Changes in gut microbiota can promote intestinal tumor development by activating the epithelial calcineurin-NFAT pathway.

AbstractThe production and handling of serotonin (5‐HT) is an important determinant of colonic motility and has been reported to be altered in gastrointestinal (GI) disorders such as irritable bowel syndrome (IBS). Recent studies suggest that the intestinal microbiota and sex of the host can influence expression of genes involved in 5‐HT biosynthesis and signaling. While expression of genes in serotonergic pathways has been shown to be variable, it remains unclear whether genes within this pathway are coregulated. As a first step in that direction, we investigated potential correlations in relative mRNA expression of serotonergic genes, in the proximal colon isolated from male and female mice in different states of microbial association: germ‐free (GF), humanized (ex‐germ‐free colonized with human gut microbiota, HM), and conventionally raised (CR) mice. Among the 10 pairwise comparisons conducted between five serotonergic transcripts, Tph1, Chga, Maoa, Slc6a4, and Htr4, we found a strong, positive correlation between colonic expression of Slc6a4 and Htr4 across different colonization states and sexes. We also identified a positive correlation between the expression of Tph1 and Chga; however, there were no correlations observed between any other tested pair of 5‐HT‐related transcripts. These data suggest that correlated expression of Slc6a4 and Htr4 likely involves coregulation of genes located on different chromosomes which modulate serotonergic activity in the gut. Further work will need to be done to understand the pathways and cell types responsible for this correlated expression, given the important role of 5‐HT in gastrointestinal physiology.

Gut microbiota alterations have been described in several diseases with altered gastrointestinal (GI) motility, and awareness is increasing regarding the role of the gut microbiome in modulating GI function. Serotonin [5‐hydroxytryptamine (5‐HT)] is a key regulator of GI motility and secretion. To determine the relationship among gut microbes, colonic contractility, and host serotonergic gene expression, we evaluated mice that were germ‐free (GF) or humanized (HM; ex‐GF colonized with human gut microbiota). 5‐HT reduced contractile duration in both GF and HM colons. Microbiota from HM and conventionally raised (CR) mice significantly increased colonic mRNAs Tph1 [(tryptophan hydroxylase) 1, rate limiting for mucosal 5‐HT synthesis; P < 0.01] and chromogranin A (neuroendocrine secretion; P < 0.01), with no effect on monoamine oxidase A (serotonin catabolism), serotonin receptor 5‐HT 4 , or mouse serotonin transporter. HM and CR mice also had increased colonic Tph1 protein ( P < 0.05) and 5‐HT concentrations (GF, 17 ± 3 ng/mg; HM, 25 ± 2 ng/mg; and CR, 35 ± 3 ng/mg; P < 0.05). Enterochromaffin (EC) cell numbers (cells producing 5‐HT) were unchanged. Short‐chain fatty acids (SCFAs) promoted TPH1 transcription in BON cells (human EC cell model). Thus, gut microbiota acting through SCFAs are important determinants of enteric 5‐HT production and homeostasis.—Reigstad, C. S., Salmonson, C. E., Rainey, III, J. F., Szurszewski, J. H., Linden, D. R., Sonnenburg, J. L., Farrugia, G., Kashyap, P. C. Gut microbes promote colonic serotonin production through an effect of short‐chain fatty acids on enterochromaffin cells. FASEB J. 29, 1395‐1403 (2015). www.fasebj.org

AbstractThe alterations in resident gut microbiota seen in chronic gastrointestinal disorders have led to an increasing interest in the role of gut bacteria in maintaining intestinal barrier function. While acute alterations in colonic secretomotor function in response to pathogens have been well described, the effect of commensal bacteria on intestinal barrier function and colonic secretomotor function still remains poorly understood. Germ‐free mice represent a model system to study effect of gut microbes on host gastrointestinal physiology. The study by Lomasney et al. represents an important step in this direction by demonstrating that the colonic secretomotor function is largely preserved in germ‐free mice, hence making them a suitable model to study effect of gut microbiota on host function.

Significance Our data demonstrate that differences in host genotype that affect the carbohydrate landscape of the distal gut interact with diet to alter the composition and function of resident microbes in a diet-dependent manner.