ENHANCEMENT OF HOST-RESISTANCE AGAINST SALMONELLA-TYPHIMURIUM IN MICEFED A DIET SUPPLEMENTED WITH YOGURT OR MILKS FERMENTED WITH VARIOUS LACTOBACILLUS-CASEI STRAINS

The aim of this study was first to compare the effects of milks fermen ted with various Lactobacillus casei strains on the survival rate of m ice infected with Salmonella typhimurium. Secondly, the relationship b etween this protective effect and the non-specific immune response was studied. For each experiment, mice were randomized into groups of eig ht animals: Animals were supplemented with one of the following prepar ations for 7 days: milk fermented with one of the three L, casei strai ns (Danone strain 001 (LAB-1), LAB-2 and Yakult), yogurt (YF), a mixtu re of LAB-1 and YF (LAB-1 + YF) or milk. The survival of the animals a fter single oral S. typhimurium infection (LD50 dosage) was monitored for 2 weeks. Aii fermented milks exhibited a protective effect against S. typhimurium infection. The highest protection was obtained with LA B-1 and that of LAB-1 + YF was significantly higher than that obtained with other treatments. Circulating IgA levels, beta-glucuronidase act ivity of peritoneal macrophages and phagocytosis index were significan tly enhanced in animals supplemented with LAB-1 and Yakult. This study shows that for one bacteria species, various strains exhibit differen t effects on protection and on immune parameters. The hierarchy establ ished for survival rates does nor entirely correlate with the effects noted on immune parameters. This indicates that stimulation of non-spe cific immunity, especially on macrophage activity, is not the only mec hanism involved in protection against intestinal infections.