Researchers from the University of Birmingham have identified significant shifts in gut bacteria at the onset of inflammatory bowel disease (IBD), according to a study published in Gastroenterology. The research, which analyzed data from more than 1,700 children and adults across 11 countries, found a loss of beneficial anaerobic bacteria and a rise in oxygen-tolerant species.
Loss of beneficial anaerobes at disease onset
The study combined raw microbiome data from multiple international datasets to examine patients with Crohn’s disease and ulcerative colitis. These findings indicate that individuals newly diagnosed with these IBD subtypes lose beneficial anaerobic bacteria that assist in the digestion of complex carbohydrates.
The loss of these anaerobic species is significant because they play a critical role in maintaining the integrity of the intestinal lining. Many beneficial anaerobes are responsible for fermenting dietary fibers into short-chain fatty acids, such as butyrate, which serve as a primary energy source for the cells lining the colon and help regulate immune responses.
In place of these anaerobes, patients experience an increase in oxygen-tolerant bacteria that typically reside in the mouth but travel into the gut. The research noted that microbiome patterns varied by geographic region and that differences were observed between stool and biopsy samples, as well as between children and adults.
Our findings suggest that changes in gut oxygen levels and the migration of bacteria from the mouth to the gut may play a key role in triggering inflammation – and these patterns could pave the way for earlier diagnosis and new treatments for IBD patients.Dr. Peter Rimmer, University of Birmingham and Consultant Gastroenterologist at University Hospitals Birmingham NHS Foundation Trust
The oxygen hypothesis and oral bacteria
The research supports what scientists call the “oxygen hypothesis.” This theory suggests that increased oxygen levels within the gut lining may disrupt the microbiome’s balance, contributing to the development of the disease.
In a healthy digestive tract, the mucosal environment is strictly anaerobic. However, the oxygen hypothesis posits that during the onset of IBD, inflammation can increase the permeability of the intestinal barrier and alter local blood flow. This physiological shift can allow oxygen to penetrate the gut lumen, creating a niche for species that would otherwise be unable to survive in an anaerobic environment.
For more on this story, see What’s really going on in your gut?.
The study specifically highlights the presence of oral bacteria, such as *Granulicatella* and *Haemophilus*, within the gut. Researchers suggest these specific species may offer new targets for the prevention or treatment of IBD. This connection is part of an emerging area of study known as the “oral-gut axis,” which examines how microbial communities in the mouth interact with and potentially influence the intestinal environment during periods of systemic or localized inflammation.
Professor Tariq Iqbal, the joint senior author of the study and Director of the University of Birmingham’s Microbiome Treatment Centre, noted that the findings could support the development of innovative diagnostic tools.
Microbial species and treatment success
The relationship between gut microbiota and IBD is linked to disease progression and treatment efficacy. A systematic review published by Nih indicates that therapies such as anti-TNF medication, vedolizumab, ustekinumab, probiotics, and fecal microbiota transplantation (FMT) can alter the composition and function of a patient’s gut microbiota.
Certain bacterial species are consistently associated with how patients respond to treatment:
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* Favorable outcomes: Beneficial bacteria, such as *Faecalibacterium prausnitzii* and *Roseburia*, have been linked to positive clinical results.
* Worsening conditions: Pathogenic bacteria, including *Escherichia coli* and *Clostridioides difficile*, are associated with the progression of the disease.
While technological advancements like metagenomics allow for the identification of the genetic basis of these microbial activities, researchers noted a need for standardisation in analytical methods and more targeted research regarding specific microbial communities and treatment outcomes. Metagenomics allows scientists to look beyond mere species identification to understand the functional genetic potential of a microbial community. However, as the study noted, the microbial profile can differ significantly depending on whether a sample is taken from stool or via an intestinal biopsy. Stool samples represent the luminal environment, whereas biopsies capture the microbes interacting directly with the mucosal tissue.
Consult your healthcare provider.
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