Fecal Metabolome and Bacterial Composition in Severe Obesity: Impact of Diet and Bariatric Surgery.

The aim of this study was to monitor the impact of a preoperative low-calorie diet and bariatric surgery on the bacterial gut microbiota composition and functionality in severe obesity and to compare sleeve gastrectomy (SG) versus Roux-en-Y gastric bypass (RYGB). The study also aimed to incorporate big data analysis for the omics results and machine learning by a Lasso-based analysis to detect the potential markers for excess weight loss. Forty patients who underwent bariatric surgery were recruited (14 underwent SG, and 26 underwent RYGB). Each participant contributed 4 fecal samples (baseline, post-diet, 1 month after surgery and 3 months after surgery). The bacterial composition was determined by 16S rDNA massive sequencing using MiSeq (Illumina). Metabolic signatures associated to fecal concentrations of short-chain fatty acids, amino acids, biogenic amines, gamma-aminobutyric acid and ammonium were determined by gas and liquid chromatography. Orange 3 software was employed to correlate the variables, and a Lasso analysis was employed to predict the weight loss at the baseline samples. A correlation between Bacillota (formerly Firmicutes) abundance and excess weight was observed only for the highest body mass indexes. The low-calorie diet had little impact on composition and targeted metabolic activity. RYGB had a deeper impact on bacterial composition and putrefactive metabolism than SG, although the excess weight loss was comparable in the two groups. Significantly higher ammonium concentrations were detected in the feces of the RYGB group. We detected individual signatures of composition and functionality, rather than a gut microbiota characteristic of severe obesity, with opposing tendencies for almost all measured variables in the two surgical approaches. The gut microbiota of the baseline samples was not useful for predicting excess weight loss after the bariatric process.

Exopolysaccharides produced by intestinal Bifidobacterium strains act as fermentable substrates for human intestinal bacteria.

Eleven exopolysaccharides (EPS) isolated from different human intestinal Bifidobacterium strains were tested in fecal slurry batch cultures and compared with glucose and the prebiotic inulin for their abilities to act as fermentable substrates for intestinal bacteria. During incubation, the increases in levels of short-chain fatty acids (SCFA) were considerably more pronounced in cultures with EPS, glucose, and inulin than in controls without carbohydrates added, indicating that the substrates assayed were fermented by intestinal bacteria. Shifts in molar proportions of SCFA during incubation with EPS and inulin caused a decrease in the acetic acid-to-propionic acid ratio, a possible indicator of the hypolipidemic effect of prebiotics, with the lowest values for this parameter being obtained for EPS from the species Bifidobacterium longum and from Bifidobacterium pseudocatenulatum strain C52. This behavior was contrary to that found with glucose, a carbohydrate not considered to be a prebiotic and for which a clear increase of this ratio was obtained during incubation. Quantitative real-time PCR showed that EPS exerted a moderate bifidogenic effect, which was comparable to that of inulin for some polymers but which was lower than that found for glucose. PCR-denaturing gradient gel electrophoresis of 16S rRNA gene fragments using universal primers was employed to analyze microbial groups other than bifidobacteria. Changes in banding patterns during incubation with EPS indicated microbial rearrangements of Bacteroides and Escherichia coli relatives. Moreover, the use of EPS from B. pseudocatenulatum in fecal cultures from some individuals accounted for the prevalence of Desulfovibrio and Faecalibacterium prausnitzii, whereas incubation with EPS from B. longum supported populations close to Anaerostipes, Prevotella, and/or Oscillospira. Thus, EPS synthesized by intestinal bifidobacteria could act as fermentable substrates for microorganisms in the human gut environment, modifying interactions among intestinal populations.