The gastrointestinal epithelium is a selective barrier that allows the absorption of nutrients, electrolytes and water, but restricts the passage of larger, potentially injurious compounds such as allergens, toxins and pathogens. A defective epithelial barrier has been reported as an important pathogenic factor in many infectious, ischemic, and immune-mediated intestinal diseases and to significantly contribute to water loss in diarrhoea. Mannan oligosaccharides are mannose rich substrates, firstly obtained from yeast Saccharomyces cerevisiae cell walls, which are described to agglutinate Gram negative bacteria thus exerting beneficial effects in the prevention of intestinal infections. Recently, we have observed that β-galactomannans obtained from the carob bean gum of the Ceratonia silliqua tree, are able to reduce Salmonella Typhimurium adhesion to ileal pig cells in vitro and the expression of proinflammatory cytokines and chemokines induced by Salmonella infection⁽ Reference Badia ^{1 )}.

The aim of this study was to investigate the potential role of different products containing β-galactomannans derived from Ceratonia silliqua and Cassia obtusifolia to prevent the disruption of epithelial barrier function induced by the colonization of Salmonella enterica subsp. enterica serovar Enteritidis (Salmonella) in intestinal human Caco-2 cells in culture.

Differentiated intestinal Caco-2 cells (ATCC) were incubated with Salmonella (provided by Ignacio Badiola, Centre Recerca en Sanitat Animal, CReSA; IRTA-UAB, Bellaterra, Spain) in the apical compartment during 3 h (MOI: 10–100). To test the effect of β-galactomannans, the products (apical compartment: 10–100 μg/ml, ITPSA, Barcelona) were preincubated during 30 min before Salmonella infection. Cell viability was assessed from lactate dehydrogenase (LDH) determination in the culture medium and epithelial barrier function, from transepithelial electrical resistance (TER) and D-mannitol fluxes as previously described.

To establish the experimental conditions of epithelial barrier disruption, first, TER and D-mannitol fluxes were determined in the presence of increasing MOI and β-galactomannan concentrations in parallel to LDH release to the incubation medium. In infected cells, the results showed a significant decrease in TER and increase in D-mannitol fluxes, thus indicating an increase in paracellular permeability of the monolayer. Moreover, the addition β-galactomannans was able to prevent the effects of Salmonella on TER and D-mannitol fluxes. In conclusion, the results obtained give an additional value to mannan oligosaccharides due to its ability to prevent epithelial barrier function disruption in Salmonella infection.