Bacteroides fragilis metabolises exopolysaccharides produced by bifidobacteria

[Background] Bacteroides fragilis is the most frequent species at the human intestinal mucosal surface, it contributes to the maturation of the immune system although is also considered as an opportunistic pathogen. Some Bifidobacterium strains produce exopolysaccharides (EPS), complex carbohydrate polymers that promote changes in the metabolism of B. fragilis when this microorganism grows in their presence. To demonstrate that B. fragilis can use EPS from bifidobacteria as fermentable substrates, purified EPS fractions from two strains, Bifidobacterium longum E44 and Bifidobacterium animalis subsp. lactis R1, were added as the sole carbon source in cultures of B. fragilis DSMZ 2151 in a minimal medium. Bacterial counts were determined during incubation and the evolution of organic acids, short chain fatty acids (SCFA) and evolution of EPS fractions was analysed by chromatography.[Results] Growth of B. fragilis at early stages of incubation was slower in EPS than with glucose, microbial levels remaining higher in EPS at prolonged incubation times. A shift in metabolite production by B. fragilis occurred from early to late stages of growth, leading to the increase in the production of propionate and acetate whereas decrease lactate formation. The amount of the two peaks with different molar mass of the EPS E44 clearly decreased along incubation whereas a consumption of the polymer R1 was not so evident.[Conclusions] This report demonstrates that B. fragilis can consume some EPS from bifidobacteria, with a concomitant release of SCFA and organic acids, suggesting a role for these biopolymers in bacteria-bacteria cross-talk within the intestine.David Ríos-Covián was the recipient of a predoctoral FPI fellowship granted by MINECO. This work was financed by projects AGL2010-16525 and AGL2013-43770-R from Plan Nacional/Plan Estatal de I + D + I (Spanish Ministry of Economy and Competitiveness, MINECO) and the Grant GRUPIN14-043 from “Plan Regional de Investigación del Principado de Asturias”. Both, national and regional grants received cofounding from European Union FEDER funds.Peer Reviewe

Interactions between Bifidobacterium and Bacteroides species in co-fermentations are affected by carbon sources, including exopolysaccharides produced by bifidobacteria

Trabajo presentado en la ENGIHR Conference 2013 (The Intestinal Microbiota and Gut Health: Contribution of the Diet, Bacterial Metabolites, Host Interactions and Impact on Health and Disease), celebrada en Valencia del 18 al 20 de septiembre de 2013.The colon is a complex microbial ecosystem dominated by obligate anaerobes that reach levels up to 1011 cells per gram of intestinal content. Bacteroides and Bifidobacterium coexist in this ecosystem and they account for up to 20% and 3% of the adult human microbiota respectively. Prebiotics are defined as nondigestible food ingredients that beneficially affect the host by selectively stimulating the growth and/or activity of one or a limited number of bacterial species in the colon, thus improving host health. Bifidobacteria have traditionally been considered as the target of prebiotic action as these substrates can be directly metabolized by these microorganisms; however, some in vitro and in vivo evidences indicate that the effects of prebiotics also involve other members of the human colon microbiota through the utilization of these substrates in combination with bifidobacteria. The most well studied prebiotics to date are inulin-type fructans (1, 2). Exopolisaccharides (EPS) are complex exocellular polymers, composed of several units of monosaccharides, produced by some bacteria. Although the synthesis of EPS in vivo has not been demonstrated yet and the amount of polymer released by the producing bacteria would be presumably low, our previous work indicates that bile stimulates the production of EPS by bifidobacteria under simulated gastrointestinal conditions (3, 4). In addition, EPS could act as fermentable substrates for the human colonic microbiota (5, 6). The fermentation in fecal batch cultures of low amounts of EPS and inulin (0.3% w/v) caused shifts in the synthesis of short chain fatty acids (SCFA), which were related to variations in the levels of some intestinal microbial populations such as Bacteroides and Bifidobacterium (6). The aim of this work was to study the influence that the presence of EPS and other carbon sources (inulin and glucose) exert on the interactions between Bacteroides and Bifidobacterium.Peer Reviewe

A fast, reliable, ultra high performance liquid chromatography method for the simultaneous determination of amino acids, biogenic amines and ammonium ions in cheese, using diethyl ethoxymethylenemalonate as a derivatising agent

Derivatisation treatment with diethyl ethoxymethylenemalonate followed by ultra-HPLC allowed the simultaneous quantification of 22 amino acids, 7 biogenic amines and ammonium ions in cheese samples in under 10 min. This is the fastest elution time ever reported for such a resolution. The proposed method shows good linearity (R2 > 0.995) and sensitivity (detection limit 0.08–3.91 μM; quantification limit <13.02 μM). Intra- and inter-day repeatability ranged from 0.35% to 1.25% and from 0.85% to 5.2%, respectively. No significant effect of the cheese matrix was observed.This work was performed with the financial support of the Spanish Ministry of Economy and Competitiveness (AGL2010-18430) and EQUIP10-30 programme (FICYT).Peer Reviewe