Lactic Acid Bacteria Induce Apoptosis Inhibition in Salmonella typhimurium Infected Macrophages

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.