In recent years, interest has increased in preparations containing Brazilian açai berries (Euterpe oleracea). The açai berry extracts are characterized by a high content of organic compounds, such as proteins or lipids. Attention is drawn to the pro-health and, in particular,  antioxidant properties of that fruit. A high antioxidant potential of açai berry extracts is determined by a high content of polyphenolic compounds that can be isolated from their flesh. When consumed by humans and animals, the polyphenolic compounds  present in plant extracts have a considerable impact on the modulation of intestinal microflora. Depending on the origin and the dose of  extract used, they can become activators or inhibitors of the growth of commensal bacteria. In the research study, there was analysed the  effect of the açai berry preparation on bacteria with probiotic potential from the Lactobacillus genus. An analysis was carried out to determine the rate of biofilm formation by bacteria depending of the presence of açai berry preparation in the culture medium. It was  tested how the açai fruit preparation affected the ability of bacteria to autoaggregate and their affinity to organic solvents. The studies  performed showed the effect of açai berry preparation on the autoaggregating capacity of Lactobacillus spp. (a reduction in the  autoaggregation of Lactobacillus brevis strains and an increase in the autoaggregation of Lactobacillus casei bacteria). Among all the  tested strains of Lactobacillus spp., a reduction was reported in the biofilm formation capacity in the environments with the açai berry  preparation added. In addition, the açai berry preparation affected the donor-acceptor type of properties of Lactobacillus spp cell walls.