Enterococcus faecium SF68 enhances the immune response to Giardia intestinalis in mice.

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.

Effect of Bacillus cereus exocellular factors on human intestinal epithelial cells.

To gain insight on the biological effects of the exocellular factors produced by Bacillus cereus, culture filtrate supernatants of different strains were coincubated with differentiated Caco-2 cells. Exocellular factors were able to detach enterocyte-like cells from the substratum after 1 h of incubation. In addition, microvilli effacing and dramatic changes on the cellular surface of enterocytes were found after incubation periods as short as 20 min. Since cell detachment was not inhibited by fetal calf serum, thiol activated cholesterol-binding cytolysin, cereolysin O, does not seem to be involved. Also, translocation of phosphatidylserine from the inner to the outer leaflets of the plasma membrane was demonstrated by using fluorescein isothiocyanate (FITC)-Annexin V. In contrast to the high capability of detaching Caco-2 cells shown by all the strains under study, the mitochondrial dehydrogenase activity was lowered by culture filtrate supernatants in a strain-dependent manner. For strain M2, the decrease in dehydrogenase activity was already evident after 30 min of incubation. Production of biologically active factors depends on the growth phase, and maximal activity was found in late exponential-early stationary phases. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of concentrated exocellular factors showed a very complex scenery supporting the multifactorial character of the biological activity of B. cereus.