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The immunomodulating effect of lactic acid bacteria (LAB) on the gut associated lymphoid tissue (GALT) and the protective capacity of some of them against enteric infections is well documented. The ability of enteroinvasive pathogens to disseminate into the deep tissues by cellular apoptosis induction is also demonstrated. Peritoneal macrophages from BALB/c mice were used to performed in vitro apoptosis assays and to determine oxidant radicals production induced by Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus, against an in vitro Salmonella typhimurium infection. We determined whether or not the LAB assayed induces apoptosis inhibition of macrophages infected with the pathogen. Fluorescent DNA fragmentation assay (Tunel test) was used to investigate the ability of the LAB to inhibit macrophage's apoptosis. We determined that Lactobacillus and Streptococcus were able to inhibit the apoptosis of macrophages induced by Sal. typhimurium, L. delbrueckii ssp. bulgaricus being the more effective one. The results suggest that these microorganisms could play a role in apoptotic mechanisms, since the inhibition of it would avoid pathogen disemination. The knowledge that S. thermophilus and L. delbrueckii ssp. bulgaricus have immunopotentiation capacity led us to demonstrate that such apoptosis inhibition observed might be mediated by other process such as the release of oxidant radicals able to kill the pathogen. The preventive effect of LAB against Sal. typhimurium infection could be mediated by apoptosis inhibition. [ABSTRACT FROM AUTHOR]

In previous papers we demonstrated the influence of the oral administration of different lactic acid bacteria on the systemic immune response and the protective effect against an infection with Candida albicans in a corticoid immunosuppressed experimental model in mice. The gastrointestinal and respiratory tracts are the most common sites of entry of the infectious agents at the mucosal surfaces. The IgA secreting cells and mastocytes play an important role in host defence against pathogens. The aim of this study was to determine whether or not some lactobacilli strains have influence on the number of IgA and mast cells associated with the gut and bronchus mucosa, in mice immunosuppressed by corticoid therapy. Groups of animals were immunosuppressed by corticoid oral administration (50 mg kg-1). They were split into four experimental groups: immunosuppressed control mice and the immunosuppressed test groups, which were given L. casei, L. delbruecki subsp. bulgaricus or L. acidophilus at a concentration of 1 X 109 cells/day/mouse, on days 8 and 9 post-corticoid. We demonstrated that the lactobacilli strains assayed were able to increase the number of IgA secreting cells and mast cells associated with both gut and bronchus mucosa, the effect being more remarkable for L. delbruecki subsp. bulgaricus. The enhancement of the IgA secreting cells and mast cells, in an immunosuppressed host induced by lactobacilli administration specially by L. delbruecki subsp. bulgaricus, suggest the potential of its use as adjuvant therapy to protect mucosal surfaces. [ABSTRACT FROM AUTHOR]