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Background: Giardiasis is a common, potentially zoonotic disease, and dogs often harbor and shed cysts without showing clinical signs. Treatment with the probiotic Enterococcus faecium SF68 has been shown to stimulate mucosal and systemic immunity in a variety of animal models and in young dogs, and to reduce giardial cyst and antigen shedding in rodents., Hypothesis: Adult dogs with chronic naturally acquired giardiasis will have decreased giardial fecal cyst and antigen shedding and increased innate and adaptive immunity after 6 weeks probiotic treatment with E. faecium SF68., Animals: Twenty adult dogs., Methods: After a 6-week dietary equilibration period, dogs were randomized to receive E. faecium SF68 or placebo for 6 weeks, and then crossed over to the alternate treatment. We measured cyst shedding, fecal giardial antigen, fecal immunoglobulin A (IgA) concentration, and circulating leukocyte phagocytic activity at multiple timepoints to determine the effect of E. faecium SF68 on giardiasis and immune responses in these dogs., Results: No differences were observed between placebo or E. faecium SF68 treatment for giardial cyst shedding, fecal antigen shedding, fecal IgA concentration, or leukocyte phagocytic activity., Conclusions: Short-term treatment with E. faecium SF68 of dogs with chronic naturally acquired subclinical giardiasis fails to affect giardial cyst shedding or antigen content and does not alter innate or adaptive immune responses.

We studied the ability of the probiotic organism Enterococcus faecium SF68 to antagonize Giardia intestinalis infection in mice. Oral feeding of E. faecium strain SF68 starting 7 d before inoculation with Giardia trophozoites significantly increased the production of specific anti-Giardia intestinal IgA and blood IgG. This humoral response was mirrored at the cellular level by an increased percentage of CD4(+) T cells in the Peyer's patches and in the spleens of SF68-fed mice. The improvement of specific immune responses in probiotic-fed mice was associated with a diminution in the number of active trophozoites in the small intestine as well as decreased shedding of fecal Giardia antigens (GSA65 protein). The ability of SF68 to stimulate the immune system at both mucosal and systemic levels highlights mechanisms by which this probiotic might antagonize pathogens in vivo. Taken together, the data demonstrate the strong potential of strain SF68 to prevent protozoa from causing intestinal infections.

This study describes the in vivo activity of Lactobacillus johnsonii La1 (NCC533) in Giardia intestinalis-infected gerbils (Meriones unguiculatus). Daily administration of lactobacilli in the drinking water from 7 days before inoculation with Giardia trophozoites efficiently prevented G. intestinalis strain WB clone C6 from infecting gerbils. More specifically, shedding of fecal Giardia antigens (GSA65 protein) was diminished in the La1-treated group, and resolution of infection was observed by 21 days postinoculation. Histology and analysis of enzymatic markers of microvillus membrane integrity revealed that probiotic administration also protected against parasite-induced mucosal damage. In addition, a cellular response to Giardia antigens was stimulated in spleen cells from La1-treated gerbils. Results show for the first time the antigiardial effect of probiotic lactobacilli in vivo and provide further insight into the antagonistic properties of lactic acid bacteria against protozoa involved in intestinal infections.