Three bacteriocin-producing bifidobacterial isolates from newborns were identified as Bifidobacterium thermacidophilum (two strains) and B. thermophilum (one strain). This study was undertaken to evaluate the ability of these strains to compete with food-borne Listeria monocytogenes for adhesion and invasion sites on Caco-2 and HT-29 cells. The bifidobacteria adhered at levels ranging from 4% to 10% of the CFU added, but none of the bifidobacteria were able to invade cells. The abilities of Listeria to adhere to and to invade cells varied widely depending on the strain tested. Three groups of Listeria were identified based on invasiveness: weakly invasive, moderately invasive, and highly invasive strains. One strain from each group was tested in competition with bifidobacteria. B. thermacidophilum RBL70 was the most effective in blocking invasion of Listeria, and the decreases in invasion ranged from 38% to 90%. For all three bifidobacterial strains, contact between the cell monolayer and the bifidobacteria for 1 h before exposure to Listeria increased the degree of inhibition. Finally, visualization of competition for adhesion sites on cells by fluorescent in situ hybridization suggested that the two bacteria tended to adhere in close proximity.
This study evaluated the effect of the probiotics Pediococcus acidilactici and Saccharomyces cerevisiae boulardii on the intestinal colonization of O149 enterotoxigenic Escherichia coli harbouring the F4 (K88) fimbriae (ETEC F4) and on the expression of ileal cytokines in weaned pigs. At birth, different litters of pigs were randomly assigned to one of the following treatments: 1) control without antibiotics or probiotics (CTRL); 2) reference group in which chlortetracycline and tiamulin were added to weanling feed (ATB); 3) P. acidilactici; 4) S. cerevisiae boulardii; or 5) P. acidilactici + S. cerevisiae boulardii. Probiotics were administered daily (1 × 109 CFU per pig) during the lactation period and after weaning (day 21). At 28 days of age, all pigs were orally challenged with an ETEC F4 strain, and a necropsy was performed 24 h later. Intestinal segments were collected to evaluate bacterial colonization in the small intestine and ileal cytokine expressions. Attachment of ETEC F4 to the intestinal mucosa was significantly reduced in pigs treated with P. acidilactici or S. cerevisiae boulardii in comparison with the ATB group (P = 0.01 and P = 0.03, respectively). In addition, proinflammatory cytokines, such as IL-6, were upregulated in ETEC F4 challenged pigs treated with P. acidilactici alone or in combination with S. cerevisiae boulardii compared with the CTRL group. In conclusion, the administration of P. acidilactici or S. cerevisiae boulardii was effective in reducing ETEC F4 attachment to the ileal mucosa, whereas the presence of P. acidilactici was required to modulate the expression of intestinal inflammatory cytokines in pigs challenged with ETEC F4.
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