Postoperative Changes in Fecal Bacterial Communities and Fermentation Products in Obese Patients Undergoing Bilio-Intestinal Bypass

Abstract

We assessed the gut microbial ecology of 11 severely obese patients before and after bilio-intestinal bypass (BIB). Fecal samples were evaluated for microbial communities using 16S rDNA Illumina sequencing, real-time PCR targeting functional genes, and gas chromatography of short chain fatty acids (SCFAs). At 6 months after surgery, subjects exhibited significant improvements in metabolic markers (body weight, glucose, and lipid metabolism) compared with baseline. The fecal microbiota of post-surgery individuals was characterized by an overall decrease of bacterial diversity, with a significant reduction in Lachnospiraceae, Clostridiaceae, Ruminococcaceae, Eubacteriaceae, and Coriobacteriaceae. On the contrary, there were significant increases of genera Lactobacillus, Megasphaera, and Acidaminococcus and the family Enterobacteriaceae. The pH was decreased in fecal samples from patients after BIB and SCFA profiles were altered, with lower percentages of acetate and propionate and higher levels of valerate and hexanoate. Some changes in the bacterial populations were associated with variations in the patients' metabolic health parameters, namely Gemmiger and glucose, Lactobacillus and glucose, and Faecalibacterium and triglycerides. The results from this study of BIB patients furthers our understanding of the composition of gut microbiota and the functional changes that may be involved in improving obesity-related conditions following weight-loss surgery.

Keywords: 16S rRNA; bariatric surgery; gut microbiota; illumina sequencing; obesity; short chain fatty acids; weight loss.

Figure 1

Alpha diversity metrics (Chao 1, Shannon and Simpson indices) of OTU-level fecal bacterial communities from obese individuals; each point represents a sample. Paired Student's t-test was performed to compare alpha diversity estimates before and after bilio-intestinal bypass. Asterisks indicate statistical significance (^*P < 0.05; ^***P < 0.001).

Figure 2

Non-metric multidimensional scaling (NMDS) ordination plot based on Bray-Curtis dissimilarities between OTU-level fecal bacterial communities in obese individuals before and after bilio-intestinal bypass.

Figure 3

Hierarchical clustering (A) and a barplot of relative abundances (B) of bacterial genera found within the fecal communities of obese patients. Only genera with a relative abundance ≥5% in at least one subject are represented. The dendrograms were calculated using Spearman's rank correlation and Ward-linkage clustering.

Figure 4

Histogram of the linear discriminant analysis (LDA) scores for differentially abundant bacterial clades in fecal samples between obese individuals before and after bilio-intestinal bypass. Negative (red bars) LDA scores represent bacterial groups over-abundant in post-surgery samples while positive (green bars) represent bacterial groups overrepresented in pre-surgery samples.

Figure 5

Abundance of metabolic functional genes in the fecal microbiota of obese individuals before and after bariatric surgery as determined by qRT–PCR. Genes targeted included BcoAT for butyrate producers, acs for acetogens, mcrA for methanogens, and dsrA for sulfate reducers. Values are log means ± SD. Paired Student's t-test was performed on log-transformed data. Asterisks indicate statistical significance (^**P < 0.01; ^***P < 0.001).

Figure 6

Levels of bacterial metabolites in the fecal samples of obese individuals before and after bilio-intestinal bypass. Individual short chain fatty acids (SCFAs) are shown as mean percentages of the total SCFA concentration. Values are means ± SD. Wilcoxon signed-rank test was performed to compare metabolites values before and after bilio-intestinal bypass. Asterisks indicate statistical significance (^*P < 0.05; ^**P < 0.01).