Gut microbiome in Crohn’s disease (CD) and ulcerative colitis (UC), the two main forms of inflammatory bowel disease (IBD), has been previously shown to have a reduced microbial diversity and may play a role in their aetiology and pathogenesis. However, until now no clear comparison between dysbiosis in CD and in UC has been investigated in a large cohort.
A recent study, led by Dr. Chaysavanh Manichanh from the Group of Physiology and Digestive Physiopathology of the Vall d’Hebron Research Institute in Barcelona (Spain), has identified for the first time a group of 8 bacterial taxa that could discriminate CD and non-CD independently of geographical region.
By using a 16S ribosomal ribonucleic acid (rRNA) gene sequencing approach, the researchers analysed a Spanish cohort consisting of 178 participants: 34 patients with CD, 33 patients with UC, 36 and 35 healthy relatives of the patients with CD and UC, respectively, and 40 healthy controls not related to the patients. A total of 415 stool samples were analysed. There was also a validation cohort of 2045 individuals with and without IBD from Spain, Belgium, the UK and Germany, including healthy controls (n=1247), CD (n=339), UC (n=158), IBS (n=202) and anorexia (n=99). The Spanish IBD cohort allowed researchers to identify microbial biomarkers for CD and the validation cohort was used to validate the results.
Dysbiosis was found significantly greater in patients with CD than with UC, as shown by a lower microbial diversity, a more altered microbiome composition and a more unstable microbial community, which is known because samples at different time points were collected. Besides this, eight microbial groups were proposed to discriminate CD from non-CD including Faecalibacterium, an unknown Peptostreptococcaceae, Anaerostipes, Methanobrevibacter, an unknown Christensenellaceae, Collinsella, Fusobacterium and Escherichia, with the last two being the most detected in Crohn’s patients.
Faecal calprotectin (FC), a marker of intestinal inflammation, was also measured in a subset of 122 Spanish participants (patients with CD and UC and their healthy relatives) at baseline and after 1 year in remission, or at recurrence of symptoms. Although during remission FC was significantly higher in patients with CD and UC than in their healthy relatives, FC concentration did not discriminate between patients with CD and UC, either during remission of at recurrence.
This is the first study in which samples from adult patients with IBD have been collected throughout a year. This design helped researchers detect the microbial biomarkers in 80% of the CD patients, when compared to the whole cohort (i.e. sensitivity) and with a specificity of 94%, 94%, 89% and 91% comparing CD versus healthy controls, patients with anorexia, IBS and UC, respectively.
In conclusion, these results show that CD and UC are two distinct subtypes of IBD at the microbiome level. This novel finding could offer a non-invasive way for diagnosing CD and perhaps allow the design of more personalized therapeutics.
Pascal V, Pozuelo M, Borruel N, Casellas F, Campos D, Santiago A, et al. A microbial signature for Crohn’s disease. Gut. 2017; doi: 10.1136/gutjnl-2016-313235.
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