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18 February 2019

Investigating the importance of bacteroides fragilis in inflammatory bowel disease

A paper was recently published which investigated the importance of a species of bacterium found within the lower gut and its possible effect on IBD


Bacteroides fragilis is a species of bacterium found within the lower gut of approximately two thirds of individuals (unpublished observation from our lab). 

B. fragilis is capable of synthesising multiple varieties of an outer capsule layer. The most studied component of the capsule is known as polysaccharide A (PSA) due to its ability to modulate the host immune system and therefore is considered beneficial to gastrointestinal health.

The research team at King's College London's Faculty of Dentistry, Oral & Craniofacial Sciences collected biopsy samples from individuals undergoing a diagnostic colonoscopy and for each sample used a method that calculated the percentage of the B. fragilis population with the PSA gene ‘on’.

Inflammatory Bowel Disease (IBD) is a chronic inflammatory condition of the gut that can severely affect quality of life. They found that individuals with IBD have a significantly lower percentage of PSA turned on than healthy individuals.

The research group also discovered that individuals with a subtype of B. fragilis that produce a potentially damaging toxin, known as B. fragilis toxin (BFT), also have a lower percentage with the PSA gene in the on position.

Altogether, these findings show that a low percentage of PSA on is associated with poor gastrointestinal health.

As a result the group hypothesised that the anti-inflammatory molecule IL-10 may mediate the link between PSA and gut inflammation but subsequently found no direct correlation.

Lucy Blandford, PhD student concludes: "Further investigation is therefore warranted to discover what environmental conditions control PSA on/off, and if PSA is linked to the severity of IBD."


"Promoter orientation of the immunomodulatoryBacteroides fragilis capsular polysaccharide A (PSA) is off in individuals with inflammatory bowel disease (IBD)" by Blandford, Johnston, Sanderson, Wade and Lax was published 7 February 2019 in Gut Microbes.