| Summary: | Furunculosis diseases causes the fish-farming industry severe economic losses. The causative bacterial agent, Aeromonas salmonicida, is reported to infect and translocate via the gastrointestinal tract. Experimental fish underwent a two week feed trial with diets of commercial feed with the addition of one of two feed additives, a probiotic, Bactocell containing P. acidilactici, and prebiotic AGRIMOS, containing mannan-oligosaccharides. The anterior intestine of the Atlantic salmon (Salmo salar) was then exposed ex-vivo to PBS (control), Aeromonas salmonicida (pathogen) and Pediococcus acidilactici (probiotic) bacteria at 8.45x106 and 9.50x106 viable bacteria per milliliter respectively and a probiotic pathogen mix. Changes in histology and gene expression in the anterior intestine were assessed using QRT-PCR, light and electron microscopy. A control group were fed the commercial diet with no feed additive and exposed to the same exposures as the experimental diets. Samples exposed only to PBS showed no signs of damage, when analysed qualitatively with scanning electron microscopy (SEM). However, exposure to the pathogenic bacteria resulted in damaged epithelial cells and microvilli in all feed groups, but to a lesser extent in the diets containing feed additives. Co-incubation of the intestine with the pathogen and P. acidilactici reduced the levels of damage seen, but did not reverse the damaging effects caused by the A. salmonicida. Gene expression of the pro-inflammatory cytokine IL-1β showed a significant reduction as a result of the co-incubation of probiotic and pathogen in the prebiotic fed group, compared to the PBS exposure. Histological analysis showed an increase in perimeter ratio of the intestine in the feed additive groups, as well as a reduced laminar propria width. Goblet cell counts per 100 enterocytes were also significantly higher in the prebiotic feed group after exposure to PBS. On the basis of these results it can be suggested that the probiotic bacterium, P. acidilactici and prebiotic feed additive is able to, at some extent, modify the anterior intestine of Atlantic salmon and reduce damage when exposed to Aeromonas salmonicida.
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