Role of Intestinal Microbiota in Ulcerative Colitis

layer of UC patients and found that the mucus layer of the left colon and rectum was significantly
thinner in the UC patients compared to the control group, and that areas of acute inflamed
mucosa were denuded of mucus layer. It has previously been hypothesized that Akk. muciniphila
could be a causal factor for intestinal inflammation, since its presence leads to degradation of the
protective mucin layer [12,58]; however, our observations contradict this hypothesis.
Lactobacillus spp. was significantly less abundant in fecal microbiota of UC patients in relapse than
in that of healthy controls (Table 3). To our knowledge, this has not previously been reported.
Species of Lactobacillus, although constituting less than 2% of the total intestinal population, are
considered to be beneficial commensal enteric bacteria and have, accordingly, been shown to
exert anti‐inflammatory effects [36,43,50,57]. Animal studies using probiotic strains have shown
that certain lactobacilli down regulate pro‐inflammatory cytokines, prevent chemical‐induced
colonic damage and reduce colonic permeability [25,36,37]. Additionally, a previous study has
shown, that increased levels of lactobacilli can help maintain remission in UC patients [59]. Hence,
the reduced content of Lactobacillus spp. in UC patients in relapse could have contributed to the
flare‐up, or alternatively these populations may have been reduced as a consequence of the
inflammatory condition. To address this issue, long term studies, where patients are followed
regularly in order to detect subtle changes in the intestinal microbiota prior to development of
symptoms clinical activity, are needed.
A reduced level of the C. leptum subgroup (include potentially important butyrate producers) has
previously been suggested to play a role in the onset of IBD flare‐ups [51,52]. The protective role
of C. leptum subgroup could be through their ability to induce regulatory T cells in the colon and
through their metabolite, butyrate that can down regulate pro‐inflammatory cytokine production
via inhibition of NF‐κβ. Both mechanisms stimulate an anti‐inflammatory state in the colon
[4,17,46]. However, possibly because of the relatively low number of patients investigated, we
found no differences in the density of C. leptum subgroup between the three groups of subjects
included in the present study. Nevertheless, there was a trend that the C. leptum subgroup was
less abundant in UC patients in remission (P=0.08) as well as in those with relapse (P=0.09)
compared to controls.
A recent metagenomic study has demonstrated the existence of enterotypes in the human gut
microbiome and identified three of them that varied in species and functional composition. Each
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