Giardia duodenalis
is a protozoan parasite responsible for giardiasis, a disease characterized by intestinal malabsorption, diarrhea and abdominal pain in a large number of mammal species. Giardiasis is one of the most common intestinal parasitic diseases in the world and thus a high veterinary, and public health concern. It is well-established that some probiotic bacteria may confer protection against this parasitein vitroandin vivoand we recently documented the implication of bile-salt hydrolase (BSH)-like activities from strain La1 ofLactobacillus johnsoniias mediators of these effectsin vitro. We showed that these activities were able to generate deconjugated bile salts that were toxic to the parasite. In the present study, a wide collection of lactobacilli strains from different ecological origins was screened to assay their anti-giardial effects. Our results revealed that the anti-parasitic effects of some of the strains tested were well-correlated with the expression of BSH-like activities. The two most active strainsin vitro, La1 andLactobacillus gasseriCNCM I-4884, were then tested for their capacity to influenceG. duodenalisinfection in a suckling mice model. Strikingly, onlyL. gasseriCNCM I-4884 strain was able to significantly antagonize parasite growth with a dramatic reduction of the trophozoites load in the small intestine. Moreover, this strain also significantly reduced the fecal excretion ofGiardiacysts after 5 days of treatment, which could contribute to blocking the transmission of the parasite, in contrast of La1 where no effect was observed. This study represents a step toward the development of new prophylactic strategies to combatG. duodenalisinfection in both humans and animals.