No distinct microbiome signature of irritable bowel syndrome found in a Swedish random population

What is it about?

In this study, we describe the faecal and gut lining microbiome composition of randomly selected urban population. A subset of these individuals suffer from irritable bowel syndrome (IBS), and all have an otherwise healthy gut. We found that diversity in the faecal microbiome is dependent on frequency of defecation and on stool consistency, but that this does not impact the bacteria attached to the gut lining. Diversity of the gut lining was affected by BMI and by stool transit time. The total number of bacterial species in a sample wasn’t affected by the transit time.

The bacterial communities observed in faecal samples were very different from those attached to the gut lining. But even if he main difference is between sample types, many species show a linear correlation in their abundance in faeces and in the gut lining, showing that these communities are in contact and are affected by their host. Since these two different communities are affected by different external pressures, and choosing which one to analyse will be important for future studies focusing on different diseases.

Another intriguing aspect of our observations is that gut bacterial diversity has a strong connection with self-rated health, that is, how healthy a person feels themselves to be. Self-rated health is correlated anxiety, depression and to the total amount of gut-related symptoms, but none of these factors, by themselves or in combination, were correlated to diversity. Most diagnoses that have been studied so far in connection to the gut microbiota have shown decreased bacterial richness, so it is not entirely surprising that those persons with poor self-rated health might have a lower gut microbiome richness. Still, there is an intriguing possibility of a connection between the general feeling of health and the richness of the gut microbiome, somehow mediated by the immune system or the gut-brain axis.

A greater spread in community types in the gut lining bacteria was observed for both underweight and overweight individuals, as well as for those with poor self-rated health. This observation is reminiscent of the “Anna Karenina hypothesis”, that is, that all healthy guts are similar, but each diseased gut is diseased in its own way.
Unlike previous IBS studies, here we did not find any significant differences in the faecal sample composition of IBS subjects and healthy controls. An important difference between our study and previous ones is that we excluded all individuals that had some kind of diagnosis in their colonoscopy. The degree of heterogeneity in the gut of healthy individuals is similar to the degree of difference between healthy and IBS individuals, so it is quite likely that no simple model of “one bug, one disease” applies to this intriguing disease.

Featured Image