“Immune mechanisms induced by fermented milk containing the probiotic strain l. Casei dn-114001 in the protection of Salmonella enteritidis serovar Typhimurium infection

MALDONADO GALDEANO, CAROLINA; DE MORENO DE LEBLANC, ALEJANDRA; CARMUEGA, ESTEBAN; WEILL, RICARDO; PERDIGÓN, GABRIELA.

Lisboa-Portugal

Congreso; Vaccine for enteric diseases Congress; 2007

Introduction: Salmonella enteritidis serovar Typhimurium, enteropathogenic and enterohemorrhagic Echerichia coli are the most important microorganisms causing of diarrhoea in the world. These infection leads to the deaths of hundred of children by year in developing countries.  Salmonella enteritidis serovar Typhimurium is an invasive bacterium infecting the host by attaching to the surface of M cells from Peyer’s patches or to the intestinal epithelial cells, and translocates through the intestinal barrier to invade the immune cells associated to the gut and to disseminate toward deep tissues. Much work has been done to characterize the biology of the infection and the virulence mechanisms used by this bacterium to cause diarrhoeal disease. Despite these advances, it is now becoming clear that the host also play an important role in both, the defence against the pathogen an in causing the tissue pathology and diarrhoeal disease induced during infection. Probiotic bacteria suspension or fermented milk containing probiotics can stimulate the mucosal immune system as we and others have demonstrated. These preparations open a big possibility in the prevention against enteropathogen infections. In a previous work we demonstrated the effectiveness of fermented milk containing the probiotic strain Lactobacillus casei DN-114001 against in an E. coli enteroinvasive infection using mouse as experimental model. Aims: The present study was carried out to investigate the effect of this fermented milk in the protection against Salmonella enteritidis serovar Typhimurium (Salmonella Typhimurium) and to determine the mechanisms involved in such protective effect in a mouse model. Methodology: three groups of BALB/c mice were given: 1- Fermented milk (FM) during 5 days before the challenge with Salmonella Typhimurium and again FM for 7 days (FM-S-FM). 2- Fermented milk for 7 days after challenge with the pathogen (S-FM). 3- Untreated control animals, challenged with Salmonella Typhimurium (S). 7 days post challenge, the animals were sacrificed. The liver was removed and the intestinal fluid was collected. Total secretory IgA (S-IgA) in the intestinal fluid and microbicidal activity of macrophages isolated from the Peyer’s patches and peritoneum were measured. Results: The number of Salmonella Typhimurium UFC/ml in the liver was significantly diminished in the S-FM group compared with the control group S. This diminution agrees with the increase in the anti-Salmonella Typhimurium-specific IgA in that group. The FM-S-FM group was less effective in the protection against the pathogen. The colonization assays and the specific-IgA release did not show significant differences with the control group. As regard to the microbicidal activity, measured in macrophages isolated from the peritoneum or the Peyer’s patches, we did not find difference with the control. Total IgA levels were significantly increased only in animals given FM after pathogen challenge. Conclusions: We demonstrated that the protective role of the FM containing the probiotic strain L. casei DN-114001 against Salmonella Typhimurium infection was remarkable when the FM is administered after challenge with the pathogen. To determine the reason why the FM-S-FM group was less effective than the previous one, studies involving the expression of TLR-4 are in progress. The negative microbicide activity found would mean that the mechanisms through NADPH oxidase, with oxidant radical release, would not to be involved in the protective effect of this FM. The production and release of specific S-IgA anti-pathogen would be one of the most important mechanisms induced by FM to control Salmonella dissemination.