Biofilms composed of foodborne bacterial pathogens pose a significant challenge to food safety, as they enhance the microbial persistence in processing environments. Quorum sensing (QS), particularly the autoinducer-2 (AI-2) signaling system, which is widely conserved among both Gram-positive and Gram-negative bacteria and is involved in both intra- and inter-species bacterial communication, is employed to regulate group behaviors based on cell density and plays a crucial role in biofilm formation by pathogens such as Listeria monocytogenes and Staphylococcus aureus. Lactic acid bacteria (LAB) have been used for centuries in food fermentation to improve the sensory and nutritional profiles and preserve against detrimental microflora. The use of LAB and/or their metabolites as natural quorum-sensing inhibitors (QSIs) may represent a promising, eco-friendly antibiofilm strategy. This study investigates the ability of LAB-derived cell-free supernatants (CFSs) to interfere with AI-2-mediated QS and inhibit biofilm formation in monocultures of L. monocytogenes and S. aureus. To achieve this, a collection of 89 foodborne LAB isolates was initially screened for either AI-2 production or inhibition using Vibrio harveyi luminescence assays. Twenty CFSs displaying AI-2 interference activity were then selected and further evaluated for their antibiofilm potential at sub-minimum inhibitory concentrations (sub-MICs) using microtiter plate biofilm assays based on crystal violet staining. The results revealed that 61.8% (55/89) of the tested CFSs contained AI-2-like signals, while 28.1% (25/89) demonstrated significant AI-2-QSI activity. Almost all of the tested CFSs exhibiting AI-2 QS interference, except for one, significantly limited L. monocytogenes biofilm formation, while one of them also reduced the biomass accumulation of S. aureus biofilms significantly (by 47.8%). These findings highlight the potential of crude LAB extracts to disrupt QS and serve as novel antibiofilm agents in food safety applications. Further research will examine their efficacy against multi-species biofilms under food-relevant conditions.

This project was funded by the National Recovery and Resilience Plan Greece 2.0, European Union—NextGenerationEU (HFRI Project 15572).