Here, we characterized released-exopolysaccharides (r-EPS) from Lactobacillus acidophilus A4 with the goal of identifying natural compounds that represses biofilm formation. In plastic 96-well microplates that contained 1.0 mg/ml of r-EPS, enterohemorrhagic Escherichia coli (EHEC) biofilms were dramatically decreased by 87% and 94% on polystyrene and polyvinyl chloride (PVC) surfaces, respectively. In the presence of r-EPS, neither their growth rate nor their autoinducer-2-like activity was affected on the EHEC O157:H7. Importantly, consistent reduction in biofilm formation was also observed when r-EPS was applied to the continuous-flow chamber models. In addition, we found that adding r-EPS significantly repressed biofilm formation by affecting genes related to curli production (crl, csgA. and csgB) and chemotaxis (cheY) in transcriptome analysis. Furthermore, these r-EPS Could prevent biofilm formation by a wide range of Gram-negative and -positive pathogens. This property may lead to the development of novel food-grade adjuncts for microbial biofilm control. (c) 2008 Elsevier Inc. All rights reserved.