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Author(s): Sabine Amani Tanner[sup.1] , Christophe Chassard[sup.1] , Annina Zihler Berner[sup.1] and Christophe Lacroix[sup.1] Background Salmonella are highly prevalent in swine where they affect about one third of all production [...], Background Probiotics and prebiotics are promising strategies to counteract Salmonella prevalence in swine. In the present study, we investigated the effects of prebiotics (fructo- (FOS), galacto- (GOS) and mannan- (MOS) oligosaccharides) and the bacteriocinogenic Bifidobacterium thermophilum RBL67 (RBL67) on Salmonella enterica subsp. enterica serovar Typhimurium N-15 (N-15) colonization using the PolyFermS in vitro continuous fermentation model simulating the swine proximal colon. Material and methods The PolyFermS model was designed with a first-stage reactor containing immobilized fecal pig microbiota. This reactor continuously inoculated five parallel second-stage reactors, a control and four treatment reactors, all operated with proximal colon conditions. FOS and GOS (5.2g/day), and MOS (half dosage) and RBL67 (10.sup.8 copy numbers/mL applied daily) were tested on the ability of N-15 to colonize reactors, inoculated with the same microbiota. Reactor effluents were collected daily and analyzed for microbial composition (quantitative PCR and 454 pyrosequencing of 16S rRNA gene pool) and main metabolites (HPLC). Results RBL67 and N-15 were shown to stably colonize the system. Colonization of N-15 was strongly inhibited by FOS and GOS, whereas addition of RBL67 alone or combined with MOS showed intermediate results. However, the effect of FOS and GOS was enhanced when prebiotics were combined with a daily addition of RBL67. FOS and GOS increased the total short chain fatty acid production, especially acetate and propionate. RBL67 combined with FOS additionally stimulated butyrate production. Conclusions Our study demonstrates the suitability of the porcine PolyFermS in vitro model to study nutritional effects of pro- and prebiotics on gut microbiota composition and activity. It can further be used to monitor Salmonella colonization. The inhibition effects of FOS and GOS on N-15 colonization are partly due to an increased acetate production, while further antimicrobial mechanisms may contribute to an enhanced inhibition with prebiotic-RBL67 combinations. A future direction of this work could be to understand the anti-Salmonella effects of Bifidobacterium thermophilum RBL67 in the presence of prebiotics to unravel the mechanism of this probiotic:pathogen interaction. Keywords: Bifidobacterium thermophilum RBL67, Swine, Intestinal fermentation model, Prebiotics, Probiotics, Salmonella enterica subsp. enterica serovar Typhimurium N-15

In vitro gut modeling provides a useful platform for a fast and reproducible assessment of treatment-related changes. Currently, pig intestinal fermentation models are mainly batch models with important inherent limitations. In this study we developed a novel in vitro continuous fermentation model, mimicking the porcine proximal colon, which we validated during 54 days of fermentation. This model, based on our recent PolyFermS design, allows comparing different treatment effects on the same microbiota. It is composed of a first-stage inoculum reactor seeded with immobilized fecal swine microbiota and used to constantly inoculate (10% v/v) five second-stage reactors, with all reactors fed with fresh nutritive chyme medium and set to mimic the swine proximal colon. Reactor effluents were analyzed for metabolite concentrations and bacterial composition by HPLC and quantitative PCR, and microbial diversity was assessed by 454 pyrosequencing. The novel PolyFermS featured stable microbial composition, diversity and metabolite production, consistent with bacterial activity reported for swine proximal colon in vivo. The constant inoculation provided by the inoculum reactor generated reproducible microbial ecosystems in all second-stage reactors, allowing the simultaneous investigation and direct comparison of different treatments on the same porcine gut microbiota. Our data demonstrate the unique features of this novel PolyFermS design for the swine proximal colon. The model provides a tool for efficient, reproducible and cost-effective screening of environmental factors, such as dietary additives, on pig colonic fermentation. [ABSTRACT FROM AUTHOR]