Aims: The aim of this study was to investigate the effect of clary sage, juniper, lemon and marjoram essential oils (EOs) and their major components on the formation of bacterial and yeast biofilms and on the inhibition of AHLmediated quorum sensing (QS). Methods and Results: Biofilm formation was measured by crystal violet and resazurin staining, and QS inhibition was detected by paper disc diffusion assay. Marjoram EO inhibited Bacillus cereus, Pichia anomala, Pseudomonas putida and mixed-culture biofilm formation of Ps. putida and Escherichia coli and showed the best QS inhibitor effect on Chromobacterium violaceum. For B. cereus, all components showed better antibiofilm capacity than the parent EOs. Lemon EO inhibited E. coli and mixed-culture biofilms, and cinnamon was effective against the mixed forms. Scanning electron microscopy showed the loss of three-dimensional structures of biofilms. Conclusions: The EOs and components used seem to be good candidates for prevention of biofilm formation and inhibition of the AHL-mediated QS mechanism. Significance and Impact of the Study: Biofilm formation on foods and food industrial equipment is a serious problem causing food spoilage and emergence of foodborne diseases. This article highlights the importance of studying EOs as potential disinfectants and food preservatives.

Phenolic compounds and extracts with bioactive properties can be obtained from many kinds of plant materials. These natural substances have gained attention in the food research as possible growth inhibitors of foodborne pathogenic and spoilage bacteria. Many phenolic-enriched plant extracts and individual phenolics have promising anti-quorum sensing potential as well and can suppress the biofilm formation and toxin production of food-related pathogens. Various studies have shown that plant phenolics can substitute or support the activity of synthetic food preservatives and disinfectants, which, by the way, can provoke serious concerns in consumers. In this review, we will provide a brief insight into the bioactive properties, i.e., the antimicrobial, anti-quorum sensing, anti-biofilm and anti-enterotoxin activities, of plant phenolic extracts and compounds, with special attention to pathogen microorganisms that have food relation. Carbohydrase aided applications to improve the antimicrobial properties of phenolic extracts are also discussed.

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Biofilms are surface-associated microbial communities resistant to sanitizers and antimicrobials. Various interactions that can contribute to increased resistance occur between the populations in biofilms. These relationships are the focus of a range of studies dealing with biofilm-associated infections and food spoilage. The present study investigated the effects of cinnamon (Cinnamomum zeylanicum), marjoram (Origanum majorana), and thyme (Thymus vulgaris) essential oils (EOs) and their main components, i.e., trans-cinnamaldehyde, terpinen-4-ol, and thymol, respectively, on single- and dual-species biofilms of Escherichia coli, Listeria monocytogenes, Pseudomonas putida, and Staphylococcus aureus. In dual-species biofilms, L. monocytogenes was paired with each of the other three bacteria. Minimum inhibitory concentration (MIC) values for the individual bacteria ranged between 0.25 and 20 mg/mL, and trans-cinnamaldehyde and cinnamon showed the highest growth inhibitory effect. Single-species biofilms of L. monocytogenes, P. putida, and S. aureus were inhibited by the tested EOs and their components at sub-lethal concentrations. Scanning electron microscopy images showed that the three-dimensional structure of mature biofilms embedded in the exopolysaccharide matrix disappeared or was limited to micro-colonies with a simplified structure. In most dual-species biofilms, to eliminate living cells from the matrix, concentrations exceeding the MIC determined for individual bacteria were required.

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