MICROBIAL REPRESENTATION ASSOCIATION WITH LEVEL OF SHORT CHAIN FATTY ACIDS IN SMALL BOWEL

Abstract BACKGROUND Small bowel microbiome and associated postbiotics understanding is still in its infancy. In intestinal bowel disease treatment, surgical interventions leading to an ostomy are often the last resort. The ileostomates and the colostomates lack the whole or part of the colonic function, respectively. In these populations, fecal effluents represent aspects of the small bowel microbial communities and associated small molecules not available in traditional stool collections. METHODS We completed a cross-sectional collection of samples from participants with digestive resections were recruited including 26 ileostomates and 23 colostomates. Additionally, 22 individuals with unaltered digestive tracts were enrolled for a total of 71 participants. Stool were self-collected in transport and storage medium. Identification and quantitation of short chain fatty acids were performed using LC MS/MS equipped with a C18 reversed phase UHPLC column. Concentrations for acetic, propionic, butyric, isobutyric, valeric, 2-methylbutyric, isovaleric, and hexanoic acid were obtained. Analysis of covariance (ANCOVA) was used to evaluate the difference in the mean SCFA concentration across the groups. Microbial membership identification was performed using 16 rDNA sequencing for a subset of 59 samples. A table of amplicon sequence variants (ASV) counts per sample was derived using the dada2 R package. Kruskal-Wallis and Post-hoc test Dunn with Benjamini-Hochberg multiple test correction were used to compare the abundance of bacteria producing and utilizing specific short chain fatty acids between the three groups. RESULTS For the eight measured short chain fatty acids, all were significantly decreased in ileostomates compared to colostomates and control group (p < 0.001). We observed significant positive correlations between microbial metabolite producers and corresponding metabolites for propionic acid, butyric acid, isobutyric acid, and isovaleric acid. For example, at the level of the population, a positive correlation was found between the abundance of butyric acid microbial producers and the butyric acid level (R=0.5, p = 7.3e-05). Conversely, a significant negative correlation between levels of acetate producers and fecal acetic acid was found in the whole population. CONCLUSION The presence of a partial colon, in colostomate, did not drastically alter the detection of the different short chain fatty acids compared to the individuals with an intact colon. In contrast the absence of a colon was associated with a significant drop in level of detected postbiotics. These findings underline the biogeographical distribution of both the microbiome and small molecules along the digestive tract.