['To assess the effect of two lactobacilli on the biological activity of enterohaemorrhagic Escherichia coli (EHEC) in vitro.', 'Strains CIDCA 133 (Lactobacillus delbrueckii subsp. lactis) and CIDCA 83114 (Lactobacillus plantarum) were studied. Hep-2 cells were used as an in vitro model to assess the biological effect of a clinical isolate of EHEC. Preincubation of cell monolayers with lactobacilli before EHEC prevented detachment of eukaryotic cells and minimizes both F-actin rearrangements and morphological alterations. Interestingly, the protective effect could not be ascribed to pathogen exclusion. In addition, viability of the lactobacilli was not necessary for protection and other species of the genus Lactobacillus failed to protect eukaryotic cells.'] Do lactobacilli antagonize biological effects of enterohaemorrhagic Escherichia coli in vitro?