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Lactobacillus rhamnosus GG (LGG), a model probiotic strain, plays an important role in immune regulatory activity to prevent and treat intestinal inflammation or diarrhea. However, the effect of the immune modulation of LGG on macrophages to prevent Salmonella infection has not been thoroughly studied. In this study, C57BL/6 mice were pre-administered LGG for 7 days continuously, and then infected with Salmonella enterica subsp. enterica serovar Typhimurium (S. Typhimurium). The results of the in vivo study indicated that LGG could reduce body weight loss, death rate and intestinal inflammatory response caused by S. Typhimurium. LGG also limited S. Typhimurium dissemination to liver and spleen, and thereby protected against infection. In vitro study, we observed that LGG enhanced the phagocytic and bactericidal ability of macrophages and upregulated M1 macrophage characters (e.g. iNOS, NO and IL-12) against S. Typhimurium. In addition, LGG also elevated IL-10 secretion, which was helpful to ameliorate intestinal inflammatory injury caused by S. Typhimurium. In conclusion, LGG could modulate M1 macrophage polarization and offer protective effects against S. Typhimurium infection. • C57BL/6 mice pre-treated with LGG could resist S. Typhimurium infection through evaluation of bodyweight loss, survival rate, and bacterial loads in liver or spleen. • LGG was also observed to upregulate IL-10-expression and ameliorate intestinal inflammatory injury caused by S. Typhimurium through pathological evaluation, at late stage of S. Typhimurium infection. • LGG modulate M1 macrophage polarization through increasing iNOS, NO and IL-12-expression, at early stage of S. Typhimurium. [ABSTRACT FROM AUTHOR]