Patients with diarrhoea-predominant irritable bowel syndrome have less microbial diversity

Researchers from the Physiology and Pathophysiology of the Digestive Tract group at Vall d’Hebron Institute of Research (VHIR) have found that patients with diarrhoea-predominant irritable bowel syndrome (IBS) and those who switch constipation and diarrhoea have less microbial diversity, specifically less butyrate and methane-producing bacteria than healthy or constipated patients. This is one of the outcomes that have been published in the Nature Scientific Reports journal as a result of this research that has been carried out using the largest cohort of patients of this disease.

In order to carry out this study conducted by Dr. Chaysavanh Manichanh, researchers have analysed the composition and the structure of the microbiome of 133 patients with irritable bowel syndrome and the same process for 66 healthy controls. Totally, 273 fecal samples were analysed as a second sample was provided by several patients a month later. The three types of IBS were included among the samples, sorted according to the patient’s clinical symptoms: patients who have diarrhoea predominant IBS, patients with constipation predominant IBS and patients with a mixed bowel pattern with both loose and hard stools.

The first results of the study report similarities among the different groups. “Patients with diarrhoea and those with a mixed bowel pattern have a similar composition of the microbiota, while the diversity of the gut flora for those patients with constipation is more similar to the one of the healthy patients”, Dr. Manichanh claims. This is a finding that proves, according to the VHIR’s researcher, that “any attempt to adjust the composition of the microbiome of the patients with IBS will not work the same way for all the patients”.

First, researchers found that patients with diarrhoea had less butyrate and methane-producing bacteria. Butyrate has been proved to contribute to the impermeability of the epithelial barrier, therefore its little presence or its absence causes the passage of microbes through the barrier to other body sites, which might affect symptoms through interaction with immune and nerve cells in the gut wall.

Then, regarding methane, VHIR researchers not only have detected that patients with diarrhoea have less methane-producing bacteria, but also that this type of bacteria which slows down gut contents are predominant among patients with constipation.

Besides these results, the study has also allowed to correlate different bacteria families with sense of bloating, abdominal pain and swelling and to identify the fact that patients who have taken antacids present with a more pathogenic bacteria family population.

After this in-depth analysis, the researchers are working on a new project in order to adjust the microbiome through the diet. But before that, they still have to properly isolate the identified bacteria to delimit the key mechanisms in the different subtypes of the irritable bowel syndrome.

Is it estimated that 11% of the population suffers from irritable bowel syndrome. Only in Vall d’Hebron, the Physiology and Pathophysiology of the Digestive Tract Unit has more than a thousand patients. However, experts indicate that the prevalence could be higher as the lack of biological markers implies that sometimes patients are diagnosed with other pathologies such as bloating or psychological stress.