Focus on the 4th biennial meeting of the ESNM

Irritable bowel syndrome and microbiota 

Irritable bowel syndrome (IBS) is a chronic disorder associated with pain and changes in fecal consistency and frequency of bowel habits. The influence of gut microbiota composition has been proposed as a target for study.[1] A decreased alpha-diversity with increased ratio Firmicutes/ Bacteroidetes and increased Streptococcus and Ruminococcus has been described. Even though the treatment with probiotics in IBS is not ready for prime time, many studies have shown promising results. Small intestinal bacterial overgrowth (SIBO) has been associated with IBS in a subset of patients and lactulose/ glucose breath test are used to diagnose SIBO.

During a Biocodex workshop entitled “Microbiome Based Strategies in IBS” Professor Magnus Simren emphasized that gut microbiota is altered in a subset of patients with IBS. An integrated framework of the pathophysiology of IBS has been proposed implying that the gut microbiota may interact with gut immune system, the epithelial barrier and the gut-brain axis. A specific gut microbial signature might be linked to IBS symptom severity. Also probiotics may produce changes in visceral hypersensitivity, neuromotor dysfunction, dysbiosis, disruption of the intestinal barrier and low grade inflammation. In fact, most meta-analyses favour the use of probiotics in IBS.[2] The problem remains in determining which probiotic is useful in each patient.

In a placebo controlled trial, a strain of Bifidobacterium has shown to be superior to placebo in the global assessment of symptom relief in IBS of all subtypes.[3] The proposed mechanism is a normalization of the balance of anti and pro-inflammatory cytokines Il-10 and Il-12.

The low FODMAP diet has been recently proposed. The long-term effect in microbiota composition and nutritional consequences deserve further studies. Responsiveness to a low FODMAP diet intervention may be predicted by fecal bacterial profiles.

Many exciting studies addressing IBS and microbiota were presented during the meeting.

Fecal microbial transplantation (FMT) has become a promising candidate in IBS treatment. However, a recent meta-analysis [4] showed no difference between placebo and FMT. The availability of a super- donor (healthy young athlete, 3 times-in-life antibiotic use) as shown in a study presented by M. El Salhy might be the key for better results.

In a poster presented by V. Passananti, Bifidobacterium infantis showed improvement in symptoms in non-responders to low FODMAP diet. The results were similar for severity and frequency of pain and abnormal distention. Also the number of severe cases of IBS was reduced by half. There was also a significant reduction of anxiety (p < 0.005) and depression (p < 0.006) scores.

The effect of a probiotic Saccharomyces boulardii (Sb) alone or multispecies (Lactobacillus casei, L. rhamnosus, L. acidophilus, L. bulgaricus, Bifidobacterium longum and B. brevis) was studied in 53 patients with bloating and abdominal pain and was presented by D. Vera in a study. Both probiotics showed a decrease in bloating and pain with a greater effect of Sb in abdominal pain relief (p < 0.001).

The impact of Saccharomyces boulardii (Sb) in IBS D with SIBO positive patients was evaluated by L. Bustos Fernandez. A trend to a greater decrease in breath test in Hydrogen excretion AUC from baseline in the Sb group was found in patients with an improvement of the IBS-SSS score and normalization of the Bristol Stool Scale as compared to control group. Faecalibacterium prausnitzii was more abundant coincidently with marked clinical improvement with Sb; stool consistency normalization (+ 120%), negative SIBO with improved IBS-related symptoms (+ 400%) and reduction of abdominal pain (- 76.5%). Mycobiota analyses showed significant modifications in Sb and phylogenic related lineage (Saccharomyces [+ 27%], Debaryomyces [– 88%]) and Filobasidium [> 1,000%]). In addition, the genus Penicilium and upper related lineage were 100 times more abundant in SIBO negative samples after Sb treatment.

Microbiota and obesity 

The role of microbiota and obesity has gained great interest suggesting that certain microbiota signatures might increase the capacity of energy harvest.

P. Enck emphasized that a poor diversity in gut microbiota might also be used as a biomarker for obesity and that a specific microbiota signature drives individuals to prefer high caloric intake. The altered Firmicutes/ Bacteroidetes ratio has been proposed as a condition but is this not specific to obesity. This has not been confirmed in recent meta-analysis.[5]

In order to be relevant as a putative biomarker for obesity, the microbiota composition must be responsive to weight change, which is not always observed in bariatric surgery and conversely, changing the microbiota should induce weight change. Pre/probiotic nor FMT use have not accomplished with this aim.

Even though the gut microbiota is known to be involved in obesity, it not possible today to find a reliable signature as biomarker. Clinical trials in humans are interfered by daily nutrition and other factors such as probiotics, exercise and FMT.

Microbiota and brain gut axis

The gut microbiota plays a role in determining mental health and this has been targeted with the so called psychobiotics. The use of probiotics, prebiotics, diet, FMT and altering microbial consortia and metabolites represent an exciting field of investigation in stress-related disorders.

G. Clarke presented studies showing that the gut microbiota can modulate the amygdala volume and that a dendritic hypertrophy in basolateral amygdala neurons is observed in germ free animals. Serotonin and tryptophan, a serotonin precursor, play a role in the brain-gut microbiota axis. The microbiota can regulate the hippocampal serotoninergic system and tryptophan depletion normalizes depression-like behaviors. Also microbiota alteration is associated with stress induced despair behavior in rats and restoring the intestinal Lactobacillus levels normalized the stress induced behavior and ameliorated the serotonin production. A reduced microbial diversity is also present in depression with reduced Prevotella. Anhedonia-like behaviour, anxiety and tryptophan metabolism profile can be transferred via gut microbiota. The work presented by G. Clarke shows that B. longum could play an antidepressant role in rats and reduce stress response in healthy, healthy volunteers.