Role of Intestinal Microbiota in Ulcerative Colitis

Discussion and conclusion
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7. Discussion and perspectives
using SYBR‐Green based assays with primers targeting either 16S rRNA gene sequences or 16S‐23S
rRNA intergenic spacer regions. The primers were selected based on sensitivity and specificity,
which led to a limited number of Bifidobacterium species target. However, quantification of
numerous species of lactic acid bacteria found in the human gut is needed to draw any conclusions
on intragenic compositional changes from individual samples. The design of primers may give
some problems when targeting species within a genus, since primer specificity and sensitivity can
be difficult to obtain. Even though 16S rRNA gene sequences can be used for species identification
and quantification ((Matsuki et al., 1998;Byun et al., 2004;Matsuki et al., 2004) and Paper 1 – 2),
they have some limitations in discriminating species of related taxa or within the same genus, due
to high 16S rRNA sequence similarities (Fox et al., 1992). Protein‐coding genes or 16‐23S rRNA
intergenic spacer regions may be a better choice, since both exhibit higher sequence variations
than 16S rRNA gene sequences (Saikaly et al., 2007). Previous studies have used 16S‐23S rRNA
intergenic spacer regions (Haarman and Knol, 2005), as well as Paper 1 or recA (Masco et al., 2007)
to quantify species within Bifidobacterium showing high specificity.
The low levels of lactic acid bacteria derived from UC patients found in the artificial mucus layer in
Paper 2 have previously been described for bifidobacteria from mucus layer of biopsy specimens
from UC patients (Macfarlane et al., 2004;Mylonaki et al., 2005). As mentioned above, the results
from Paper 1 demonstrated low abundances of fecal lactobacilli in UC patients in relapse than in
healthy subjects, but no significant difference was observed for the fecal bifidobacteria. Low levels
of fecal bifidobacteria in UC patients in relapse have previously been described by Sokol et al.
(2009). The discrepancy in results could be due to differences in the amount of participants in the
two studies: Paper 1 is based upon six participants in each group whereas the study by Sokol et al.
(2009) covers thirteen UC patients in replase and twenty seven healthy controls. The low amount
of participants in Paper 1 is a weakness in the study, since it gives a low confidence interval (high
margin of error); hence is not as representative for a true population, as when using a high
amount of participants. Additionally, due to high inter‐individual variations significant power can
be difficult to reach.
However, when comparing Paper 1 to previous communications (Takaishi et al., 2008;Qin et al.,
2010;Arumugam et al., 2011), several similar tendencies can be found, which justifies the results
of the study.