ABSTRACT
The present studies were designed to investigate the effect of orally administered Lactobacillus casei , Lactobacillus acidophilus , Lactobacillus delbrueckii spp., bulgaricus , and Streptococcus salivarius ssp. thermophilus on local mucosal immunity in response to enteropathogens. Normal mice were protected against Salmonella typhimurium infection by previous feeding with L. casei and S. salivarius spp. thermophilus , while L. acidophilus and L. delbrueckii spp. bulgaricus were not effective. The protective effect of L. casei against S. typhimurium was associated mainly to IgA production in intestinal secretions. We observed significant differences in the intestinal fluid anti- Salmonella agglutinin titers between the Salmonella -challenged control group (without lactobacilli feeding) and mice pretreated with L. casei . The level of immunoglobulins from intestinal fluid of mice fed previously with lactic acid bacteria was measured by radial immunodiffusion assay showing in all cases an increase in the immunoglobulin concentrations. By Immunoelectrophoresis methods, we observed the presence of two lines of immunoprecipitation. When we used monospecific serum, we detected the presence of IgG and IgA. Elisa tests showed high levels of IgA to S. typhimurium in intestinal secretions of mice pretreated with L. casei , while L. acidophilus and L. delbrueckii spp. bulgaricus groups showed values at slightly higher levels than the controls. The levels of IgG to S. typhimurium were similar to controls in all cases. We did not observe antibodies against the pathogen in intestinal fluid from mice fed with S. salivarius spp. thermophilus . However, we detected anti- Streptococcus antibodies. These results show that only L. casei increases the IgA production secreted to the intestinal lumen, providing adequate defenses at mucosal surfaces, and suggest that this microorganism could be used as oral adjuvant especially to prevent enteric infections.
