IBS-associated phylogenetic unbalances of the intestinal microbiota are not reverted by probiotic supplementation Original paper

What was studied?

This study investigated the phylogenetic unbalances of the intestinal microbiota in individuals diagnosed with Irritable Bowel Syndrome (IBS) and evaluated whether these imbalances could be reverted through daily probiotic supplementation with a novel yogurt containing Bifidobacterium animalis subsp. lactis Bb12 and Kluyveromyces marxianus B0399. The primary goal was to determine if the probiotic intervention would modulate the gut microbiota composition in a way that counteracts the dysbiosis observed in IBS patients.

Who was studied?

Nineteen individuals with clinically diagnosed IBS (10 with diarrhea-predominant IBS, 5 with mixed bowel habits, and 4 with constipation-predominant IBS) participated in a monocentric trial. Their gut microbiota profiles were compared with a control cohort of 24 healthy subjects, matched for age and sex, and previously characterized using the same methodologies.

What were the most important findings?

The study demonstrated that the gut microbiota of IBS patients is significantly different from that of healthy individuals, showing distinct phylogenetic imbalances. The IBS-associated microbiota was characterized by an increased abundance of Lactobacilli, Bacillus cereus, Bacillus clausii, Bifidobacteria, Clostridium cluster IX, and Eubacterium rectale, alongside a marked depletion of the Bacteroides/Prevotella group and the Veillonella genus. Notably, several bacterial groups previously defined as pathobionts, such as members of the Enterobacteriaceae family, Enterococcus faecium, Clostridium difficile, and Campylobacter spp., were enriched in IBS patients.

Despite these findings, the probiotic intervention with B. animalis subsp. lactis Bb12 and K. marxianus B0399 did not significantly alter the microbiota composition in IBS patients. After four weeks of daily consumption, the microbial profiles of the participants showed no major shifts, with high inter-individual diversity persisting. Hierarchical clustering of microarray fingerprints before and after supplementation indicated that most samples remained largely unchanged. Additionally, measures of microbial diversity, such as Shannon and richness indices, were not impacted by the probiotic treatment. This indicates that while the probiotics may provide symptomatic relief, they do not appear to correct the underlying microbial imbalances associated with IBS.

What are the greatest implications of this study?

The findings suggest that the therapeutic benefits of probiotic supplementation in IBS may not be attributed to substantial shifts in the gut microbiota composition. The persistence of phylogenetic unbalances despite intervention implies that the mechanisms of probiotic efficacy in IBS might be independent of direct compositional changes, possibly involving modulation of immune responses or gut barrier function instead. This challenges the traditional view that microbiota normalization is a key pathway for probiotic effectiveness in IBS treatment and underscores the necessity for mechanistic studies focused on functional, rather than purely compositional, microbiota changes.