Essential Oil Efficacy Impaired by Food Residues in Food Pathogen Adhesion

Bacterial adhesion is a complex process and influenced by the properties of the bacterial cell envelops and the surfaces to which bacteria are to attach. Most abiotic surfaces adsorb materials from the environment, and a conditioning layer will thus be formed that modifies the physicochemical properties of surface and the interaction with bacteria. After adhesion, bacteria can form biofilms, which pose a persistent threat in the food industry. Essential oils have the potential to inhibit adhesion and subsequently prevent biofilm formation. The aim of our study was to inhibit the adhesion of the food-borne pathogens of Bacillus cereus, Listeria monocytogenes, Staphylococcus aureus and methicillin resistant S. aureus (MRSA) onto native and with food residue-coated stainless steel (SS) and polypropylene (PP) surfaces by cinnamon, thyme and marjoram essential oils (EOs) by determining live cell count on the surfaces. Food residues on the SS and PP slides affected both the process of bacterial adhesion and the anti-adhesion action of investigated EOs: adhesion was supported, anti-adhesion effect was reduced. Thyme EO showed the best anti-adhesion effect: in sub-lethal concentration, it completely inhibited bacterial attachment of MRSA and L. monocytogenes to surfaces. Cinnamon EO always lost its anti-adhesion effect in the presence of food residues but was able to regain it after removing animal protein from the surface. In summary, it is essential to ensure proper cleaning before applying EO-based sanitization methods to enhance the effectiveness of the chosen essential oils.