QUALITATIVE AND QUANTITATIVE EVALUATION OF GUT MICROBIAL POPULATIONS IN SEVERELY OBESE PATIENTS FOLLOWING BILIO-INTESTINAL BYPASS

Background and aim: Several recent studies showed that the altered gastrointestinal microbiota linked to obesity changes after gastric bypass in humans and rats, and it has been suggested that these changes may underlie some of the beneficial effects of bariatric surgery. Material and methods: To deeply characterize the impact of weight-loss surgery on gut microbial ecology, we collected fecal samples from severely obese patients (n=11) before and six months after bilio-intestinal bypass. Gut microbial populations were qualitatively and quantitatively evaluated by Denaturing Gel Gradient Electrophoresis (DGGE), 16S ribosomal RNA gene sequencing and real-time PCR. Results: Obese individuals were found to harbor a distinctive community dominated at the genus/species level by members of the clostridial clusters IV and XIVa, specifically Roseburia/E. rectale spp, Blautia spp, Ruminococcus spp, Dorealongicatena. Compared to pre-operative levels, the fecal microbial profiles of patients revealed a significant increase in the proportion of Lactobacillus crispatus, a major lactate producer, and in the population related to Megasphaer aelsdenii, which is known to be an efficient lactate-utilizer. At high taxonomic level, the BIBP individuals exhibited reduced Bacteroides- Prevotella, major genera of the Bacteroidetes phylum, but no significant differences in the relative abundance of Firmicutes in comparison with obese patients prior to surgery. Conclusions: The compositional shifts of the fecal microbial community observed in this study suggest a reprogramming of the bacterial fermentation routes in the gut following bilio-intestinal bypass. Further research is therefore called for to understand the implications on host energy homeostasis and support a possible contribution of gut bacteria in substantial weight loss and metabolic improvement after bariatric surgery.