P274 Effects of a bowel preparation diet on the gut microbiome

Introduction Prior to colonoscopy, patients undergo a bowel preparation regimen to clear bowel contents and optimize view of the bowel wall. In the UK, the bowel preparation regimen may involve patients undertaking either a 3-day low-fibre/low-residue diet (LRD) or a 1 day clear liquid diet (CLD) before their procedure. The day before their procedure, all patients are required to take a laxative. A low-fibre diet has been associated with reduced gut microbiome richness and diversity. A low-fibre diet has also been associated with a Bacteroides enterotype and an enrichment of Alistipes and Parabacteroides genera. A transition from a high-fibre to a low-fibre diet has been shown to result in changes in the gut microbiome within 24 hours. We present the results of an evaluation of the effects of a 3-day LRD on the gut microbiome. Methods Faecal samples were obtained from 5 healthy subjects. Samples were collected while participants were on their regular diets and immediately after undertaking a 3-day LRD. DNA was extracted from samples using PSP spin stool DNA plus kit (Stratec). The concentration of extracted DNA was determined using fluorometry. PCR was carried out on extracted DNA samples and gel electrophoresis was performed to determine the integrity of amplicons. A 2 step PCR strategy was utilized to produce amplicons for DNA sequencing specific to genes encoding highly conserved bacterial 16S ribosomal RNA samples. This yielded 25 microliter aliquots with a DNA concentration of 2 ng/microliter which were sequenced on the Illumina HiSeq platform. Statistical analysis was carried out using R (v.3.5.0). Gut microbiome compositions of participants before and after a 3-day LRD were represented using relative taxa abundance plots. The gut microbiomes of participants before and after a 3-day LRD were compared using fold change analysis to identify any differentially increasing or decreasing taxa. The gut microbiome richness of participants was determined and alpha diversity was calculated using Shannon diversity index. The beta diversity of the gut microbiomes of participants was determined using weighted unifrac distance matrix and plotted two-dimensionally using non-metric distance scaling (NMDS). Results After a 3-day LRD, there were no significant taxa abundance changes that were consistent between subjects (figure 1). A 3-day LRD did not have a significant effect on the richness and alpha diversity of the gut microbiomes of subjects. A 3-day LRD did not have a significant effect on the beta diversity of the gut microbiomes of subjects (p = 0.981). Conclusions A 3-day LRD did not have a significant effect on the gut microbiomes of participants. Combined with literature showing that laxatives have no long-lasting effects on the gut microbiome, our study shows that the bowel preparation regimen has no significant effects on the gut microbiome.