**5.1 Microbial signatures of IBD subtypes**

Gut microbiota dysbiosis has been associated with disease phenotypes in IBD and may be a causative or synergistic factor in prolonged or chronic inflammation. Microbial dysbiosis in IBD is characterized by a significant reduction in bacterial diversity and alterations in some specific taxa, including enrichment of the phyla *Proteobacteria* and *Bacteroidetes*, and a reduction in *Firmicutes* [49–52]. CD has been presented with a decrease in the proportion of Firmicutes and a slight increase in Enterobacteriaceae when compared with controls and UC patients [53]. *Bacteroides*, *Eubacterium*, *Faecalibacterium*, and *Ruminococcus* are the main bacterial genera reduced in the fecal samples of CD patients [54, 55]. A reduction in *Faecalibacterium prausnitzii* has been implicated in the etiology of CD, suggesting a critical role for the organism as an integral component of the anti-inflammatory balance in health and in CD pathogenesis. The phylum *Proteobacteria* is highly abundant in patients with active UC and decreased significantly in patients in remission, where as vice-versa for *Firmicutes*. Patients with active UC show an enrichment of *Klebsiella*, *Enterococcus*, and *Haemophilus*, while those in remission have higher numbers of *Roseburia*, *Lachnospira*, *Blautia*, and *Faecalibacterium* [56].
