PREBIOTIC POTENTIAL OF NOVEL NON-DIGESTIBLE CARBOHYDRATES FOR PREVENTION AND CONTROL OF SALMONELLA TYPHIMURIUM IN PIGS

Foodborne diseases have drawn increasing attention around the world. Salmonelloses are the second most common zoonosis in humans after campylobacteriosis in the European Union (EU). Pig, after poultry, is the second most important domestic animal species associated the outbreaks of salmonellosis in humans. In addition, pig production is the most important among the principal domestic animal species in the world. A supply of the consummers’ market with Salmonella-free pig meat would be important to animal production, as well as to human food safety. The control of this pathogen in pigsties by prebiotics is an approach that deserves consideration. A wide range of molecules including non-digestible carbohydrates have attracted increasing interest to prevent the harmful effects of pathogens such as Salmonella enterica. The aim of this research thesis is to assess the in vitro and in vivo potential of some novel carbohydrates to reduce Salmonella Typhimurium infections in weaned piglets.
Firstly, an in vitro batch fermentation system was improved by including mucus. This study investigated whether the survival of a wider number of intestinal bacterial populations is impacted by the presence of mucus and whether this dependence on mucus is influenced by the fermented ingredient. The introduction of mucins affected many microbial genera and fermentation patterns. Mucins increased final gas production with inulin and shifted short-chain fatty acid molar ratios. Lactobacillus spp. and Bifidobacterium spp. were decreased with mucins. In contrast, Proteobacteria, Verrucomicrobia, Ruminococcaceae, Bacteroidaceae (including Bacteroides spp.), and Akkermansia spp. were increased. In addition, Proteobacteria and Lachnospiraceae were promoted in the mucus compared with the broth, while Ruminococcaceae decreased. However, this impact of mucus on microbial genera and fermentation patterns was independent of the fermentation substrate.
The improved in vitro fermentation model of the pig intestines was used to assess prebiotic potential of novel non-digestible carbohydrates (NDCs) and their influence on Salmonella Typhimurium. Inulin, cellobiose, pectic- (POS), isomalto- (IMO), xylo-(XOS) oligosaccharides, and gluconic acid (GLU) were fermented for 72 h. None of the tested NDCs did inhibit Salmonella Typhimurium counts compared to control. However, inulin and IMO displayed prebiotical properties, since they supported the highest Lactobacillus and Bifidobacterium populations after 12 and 24 h of fermentation. Cellobiose and GLU also promoted Lactobacillus populations, but not Bifidobacteria. Looking at the fermentation patterns, GLU was weakly fermented but was the fastest fermenting NDC with the highest butyrate molar ratio. POS was slowly fermented, while XOS was poorly fermented. Cellobiose yielded the highest lactate molar ratio.
Finally, based on the results from the second in vitro trial and data obtained on mice, two promising prebiotics, IMO and POS were chosen to evaluate their prebiotical properties in an in vivo Salmonella Typhimurium challenge using a Trojan piglet model. IMO could be potential a prebiotic to improve performance, strengthen serum immune system, and decrease the Salmonella prevalence in piglets. POS did not present these properties.
It is concluded that although all tested NDCs did not reduce Salmonella Typhimurium growth, IMO seems the most promising prebiotic in terms of fermentation patterns, host responses, transmission and colonization of Salmonella in piglets. Cellobiose and GLU were only tested in in vitro system, but owing to their specific fermentation patterns, they deserve some attention and could also be assessed in vivo to confirm their action on pathogens.