Orally administered Lactobacillus plantarum reduces pro-inflammatory interleukin secretion in sera from Listeria monocytogenes infected mice

Lactic acid bacteria have traditionally been thought to have immunomodulating effects. To verify this property, Lactobacillus plantarum was orally administered to mice (5 x 10(7) colony forming units (c.f.u.)), prior to infection with Listeria monocytogenes in order to evaluate the host resistance against an infectious micro-organism and to better define the influence of L. plantarum on such responses. Balb/c mice were treated daily with L. plantarum or received PBS (sham-treated mice as controls) for 4 weeks. Subsequently, mice were intravenously infected with a clinical isolate of L. monocytogenes. Our study revealed that the administration of L. plantarum did not significantly increase the survival (P=0.13) of mice (fifteen in each group) after L. monocytogenes infection (10(6)c.f.u./ml), whereas a sub-lethal dose of L. monocytogenes (10(5)c.f.u./ml) was eliminated from liver and spleen 5d after the challenge in both L. plantarum- and sham-treated mice (n 5). Nevertheless, the levels of IL-1 beta and IL-6 from sera of orally administered L. plantarum were drastically reduced at 0, 4 (P<0.01) and 6d after L monocytogenes infection, whereas TNF-alpha production was unaltered. In conclusion, administration of L. plantarum reduced pro-inflammatory IL production after challenge with L. monocytogenes, although it did not significantly impact the survival of mice. We speculate that L. plantarum could exert anti-inflammatory effects, which may represent an important model to reduce inflammatory disorders. Therefore, further studies in human subjects should determine the role of L. plantarum as an immunomodulatory micro-organism and its relationship in the host protection to pathogens.