The ability of a Lactobacillus rhamnosus strain isolated from a healthy breast-fed human newborn to reduce the pathological consequences for the host due to an experimental oral infection with Salmonella enterica subsp. enterica serov. Typhimurium in vivo was determined using gnotobiotic and conventional mice. Conventional mice received 0.1mL probiotic milk (8.0 log colony-forming unit) daily for 10 days before the oral pathogenic challenge (5.0 log colony-forming unit). Then probiotic treatment was continued until the end of the experiment. Probiotic treatment in germ-free mice consisted of a single dose of the probiotic milk at the beginning of the experiment and a challenge with S. Typhimurium 10 days later (3.0 log colony-forming unit). A protective effect was observed in both gnotobiotic and conventional animals in terms of histopathologic and morphometric data, but in different anatomical sites. This protection was observed in liver and intestines, respectively, for gnotobiotic and conventional mice. However, S. Typhimurium populations were similar in the feces of both treated and control gnotobiotic mice. We conclude that a protective effect of L. rhamnosus against experimental S. Typhimurium was observed. This protection was not due to the reduction of the population of pathogenic bacteria in the intestine.