Action mechanisms of natural antimicrobials against food-borne pathogenes

Essential oils (EOs) or their components represent one of the most promising natural feasible alternatives to improve food safety, shelf-life and quality. Although their antimicrobial properties are well documented few and fragmented are the information about their mechanisms of action, cellular targets and on the stress response strategies of microorganisms after the exposure to such compounds. In this framework, the main aim of the PhD project was to investigate on the effects of one hour exposure to sublethal concentrations of selected natural antimicrobials, such as citral, carvacrol, (E)-2-hexenal and thyme EO, on the food-borne pathogens Listeria monocytogenes Scott A and Escherichia coli K12 MG1655. The action mechanisms of the natural antimicrobials and the cellular targets were studied through multiple approaches able to give information on cell morphological, physiological, transcriptome and proteome changes. The results obtained allowed to define for each strain and each antimicrobial the cell targets and the response mechanism, respectively. The use of the different multi-parametric approaches provided useful information on citral, carvacrol, (E)-2-hexenal and thyme EO action mechanisms on microbial cell targets as well as to elucidate the behavior and the stress response strategies used by Listeria monocytogenes Scott A and Escherichia coli K12 MG1655 after the one hour exposure to such natural antimicrobials. The validation in apple juice allowed to understand the real potential of one of the antimicrobials (chosen on the basis of its sensory compatibility with the food matrix) to improve food safety and shelf life. The data obtained can speed up the exploitation at industrial level of natural antimicrobials as alternative food preservatives.