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Background

The human gut harbors a diverse community of microorganisms which serve numerous important functions for the host wellbeing. Functional foods are commonly used to modulate the composition of the gut microbiota contributing to the maintenance of the host health or prevention of disease. In the present study, we characterized the impact of one month intake of a synbiotic food, containing fructooligosaccharides and the probiotic strains Lactobacillus helveticus Bar13 and Bifidobacterium longum Bar33, on the gut microbiota composition and metabolic profiles of 20 healthy subjects.

Results

The synbiotic food did not modify the overall structure of the gut microbiome, as indicated by Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis (PCR-DGGE). The ability of the probiotic L. helveticus and B. longum strains to pass through the gastrointestinal tract was hypothesized on the basis of real-time PCR data. In spite of a stable microbiota, the intake of the synbiotic food resulted in a shift of the fecal metabolic profiles, highlighted by the Gas Chromatography Mass Spectrometry Solid Phase Micro-Extraction (GC-MS/SPME) analysis. The extent of short chain fatty acids (SCFA), ketones, carbon disulfide and methyl acetate was significantly affected by the synbiotic food consumption. Furthermore, the Canonical discriminant Analysis of Principal coordinates (CAP) of GC-MS/SPME profiles allowed a separation of the stool samples recovered before and after the consumption of the functional food.

Effects of the synbiotic food on composition of the gut microbiota

PCR-DGGE analysis with universal primers targeting the V2-V3 region of the 16S rRNA gene was used to monitor the impact of the synbiotic food intake on the predominant bacterial population (Figure ). Population fingerprint profiles were compared and numerically analyzed by FPQuest Software. DGGE band profiles (mean of bands: 15.3) were stable for each subject over a month of feeding with the functional food. Only a slight difference in band richness was found between the time points of the study (T0, mean of bands: 15.8; T1, mean of bands: 14.8). DGGE bands were subjected to Mann-Whitney U-test in order to search for significant differences in the intensities between T0 and T1. No band showed a significant variation, indicating that the consumption of the synbiotic food did not alter the concentration of any major species of intestinal microbiota. Pearson correlation was used to calculate the similarity index (SI) between DGGE band profiles related to the time points T0 and T1 for each healthy volunteer (Table ). The high median value of SI (67.1%) revealed that the dominant bacterial composition remained constant over the treatment. Only 3 subjects presented SIs lower than 50% (subjects 8, 12 and 20). No subject showed significant variations between DGGE band profiles related to T0 and T1, as evaluated using the Pearson correlation analysis (P > 0.05).