AN EXPLORATORY STUDY ON THE USE OF GAMBUSIA AFFINIS AS A MODEL FOR INVESTIGATING GUT INFLAMMATION AND MICROBIOME CHANGES

A complex relationship exists between gastrointestinal commensal microorganisms and their hosts. While it is not entirely understood how commensal microbiota influence the host immune system, it is evident that the two are largely dependent on one another. Disharmony of the healthy GI tract can result in chronic inflammatory bowel diseases, such as Crohn’s disease (CD) or ulcerative colitis (UC). In the healthy GI tract, the lower intestine is largely hypoxic, thus it is expected to be largely dominated by anaerobes. However, inflammation in the large bowel results in dysbiosis of the microflora such that obligate anaerobes decrease in number while the presence of facultative anaerobes increases. As previous literature demonstrates, this could be due to the fact that inflammation in the host generates reactive nitrogen and reactive oxygen species, molecules that facultative anaerobes can use as final electron acceptors in anaerobic respiration. Further, use of antibiotics could result in persistent alterations in the gut microbiome composition that mimic the alterations seen in the inflamed gut, as antibiotic use in humans sometimes improves irritable bowel conditions and sometimes worsens them. Fish were exposed to dextran sodium sulfate (DSS) orally, with gut inflammation monitored using the MPO assay, gut nitrate levels determined, and gut microbiome community analyzed using 16S sequencing. In conclusion, inflammation levels were inconsistent, possibly because these invasive fish are so resilient and DSS levels were insufficient, or the presence of parasites as a confounding factor. Gut community changes were observed but statistical significance not established. These fish are not a good model for mammalian gut research, as they are normally dominated by facultative anaerobes, while mammalian by obligate anaerobes.In conclusion, it is possible that the amount of DSS used in this explorative study simply is not enough to induce colitis in Gambusia affinis, which are known for being rather resilient fish. Furthermore, it is possible that wild caught Gambusia have too many inherent confounding factors to be used reliably in gut microbiome research and thus further work is necessary.