Inhibition of Giardia intestinalis by extracellular factors from Lactobacilli: an in vitro study

The aim of the present work was to evaluate the effect of spent culture sup ernatants of different strains of lactobacilli on giardia trophozoites. The growth of Giardia intestinalis strain WB, as well as the attachment to the human intestinal epithelial cell line Caco-2, was evaluated by using proli feration and adhesion assays with radiolabeled parasites. In addition, scan ning electron microscopy and flow cytometric analysis were performed. The e ffect of spent culture supernatants from lactobacilli was strain dependent. Lactobacillus johnsonii La1 significantly inhibited the proliferation of G . intestinalis trophozoites. Although the effect was strongly pH dependent, it was not simply due to lactic acid. According to How cytometric analysis , trophozoites were arrested in G, phase but neither significant necrosis n or apoptosis could be detected. Bacterial cells or their spent culture supe rnatants were unable to modify, trophozoite attachment to Caco-2 cells. How ever, trophozoites treated with spent culture supernatants had little, if a ny, proliferative capacity. These results suggest that La1 produces some su bstance(s) able to inhibit proliferation of Giardia trophozoites. Partial c haracterization of the factors involved in the antigiardiasic action showed that they have a low molecular mass and are inactivated by heating. On thi s basis, it seems worthwhile to explore how colonization of the proximal sm all bowel with these lactic acid bacteria could interfere with giardiasis i n vivo.