Staphylococcus aureus is of major concern in milk industry, form farm to fork: it is one of the main pathogens responsible for mastitis and the first cause of food poisonings related to milk and milk products, in France. Contamination may come from raw milk (from mastitic cows), human carriers, who may also contaminate dairy products during manipulation, as well as strains endemic in the processing plant environment. The ability of some strains to form biofilms likely contributes to the persistence of S. aureus, by reducing efficiency of cleaning or antibacterial treatments. Likewise, biofilm have been evoked to explain chronicity of S. aureus mastitis, protecting S. aureus cells from host immune response and antibiotic treatments. Preventing biofilm formation by S. aureus thus appears as a key step in the fight against this pathogen. In the recent years, the concept of biological control has emerged as an interesting and sustainable alternative to fight against pathogens. We have recently established the capacity of L. lactis to affect S. aureus virulence expression under planktonic growth conditions and in cheese matrix (Cretenet et al., EMIR, 2011; Even et al., AEM, 2009). Here, we investigated the ability of Lactic Acid Bacteria (LAB) and Propionic Acid Bacteria (PAB) to affect S. aureus biofilm formation. Supernatants of 4 LAB and PAB species were tested for their ability to affect S. aureus biofilm formation by the crystal violet biofilm assay combined with direct visualization of biofilm using confocal microscopy. Several S. aureus strains able to produce a biofilm in various amounts, were included in the study. Results showed that LAB and PAB supernatants modulated either positively or negatively the dynamics of S. aureus biofilm formation in a strain- and species-dependent manner. These data were confirmed by direct observations of biofilms using confocal microscopy. Different biofilm properties, including biofilm thickness and density and the rate of surface colonization were modified, suggesting LAB and PAB were able to affect primary adhesion and maturation of S. aureus biofilm. Identification of mechanisms and effectors involved are under way.