| Summary: | <p>Abstract</p> <p>Background</p> <p>A growing amount of scientific evidence suggests that microbes are involved in the aetiology of irritable bowel syndrome (IBS), and the gastrointestinal (GI) microbiota of individuals suffering from diarrhoea-predominant IBS (IBS-D) is distinguishable from other IBS-subtypes. In our study, the GI microbiota of IBS-D patients was evaluated and compared with healthy controls (HC) by using a high-resolution sequencing method. The method allowed microbial community analysis on all levels of microbial genomic guanine plus cytosine (G+C) content, including high G+C bacteria.</p> <p>Methods</p> <p>The collective faecal microbiota composition of ten IBS-D patients was analysed by examining sequences obtained using percent G+C (%G+C) -based profiling and fractioning combined with 16S rRNA gene clone library sequencing of 3267 clones. The IBS-D library was compared with an analogous healthy-control library of 23 subjects. Real-time PCR analysis was used to identify phylotypes belonging to the class <it>Gammaproteobacteria </it>and the order <it>Coriobacteriales</it>.</p> <p>Results</p> <p>Significant differences were found between clone libraries of IBS-D patients and controls. The microbial communities of IBS-D patients were enriched in <it>Proteobacteria </it>and <it>Firmicutes</it>, but reduced in the number of <it>Actinobacteria </it>and <it>Bacteroidetes </it>compared to control. In particular, 16S rDNA sequences belonging to the family <it>Lachnospiraceae </it>within the phylum <it>Firmicutes </it>were in greater abundance in the IBS-D clone library.</p> <p>Conclusions</p> <p>In the microbiota of IBS-D sufferers, notable differences were detected among the prominent bacterial phyla (<it>Firmicutes</it>, <it>Actinobacteria</it>, <it>Bacteroidetes</it>, and <it>Proteobacteria</it>) localized within the GI tract.</p>
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