**5.3 Intestinal dysbiosis and infections**

*Drosophila* and its microbiome has provided invaluable information in understanding intestinal dysbiosis and chronic inflammatory infections. Two pathways that are present in *Drosophila* innate immune system to act against microbiota are immune deficiency (IMD) pathway (homologous to human NFκB pathway) and dual oxidase (DUOX) pathway. IMD pathway leads to anti-microbial peptide (AMP) synthesis whereas DUOX pathway leads to the formation of reactive oxygen species (ROS). Intestinal AMP overproduction changes the microbial community structure. This change is dysbiotic in nature because it leads to cell apoptosis of host cells [297]. IMD pathway over-activation leads to an increase in dysbiotic community structure and IMD inactivation leads to over-proliferation of community members in general [44]. Inflammatory bowel disorders also involve apoptosis of intestinal cells in humans which shows a link between the intestinal pathogenesis in both mammals and flies [297]. DUOX knockdown (DUOX-KD) flies show a high mortality rate after gut infections, which indicates DUOX-dependent ROS formation. These flies show huge amounts of microbial cells in the gut as opposed to wild-type flies. DUOX-KD flies survive normally in a GF environment. Inactivation of this pathway leads to host infections [298] whereas over-activation induces oxidative stress in host [299]. Extensive research in *Drosophila* midgut shows that intestinal epithelium damage induces inflammatory signals and growth factors to lead to ISC proliferation and tumor proliferation.
