Gene expression responses of Listeria monocytogenes Scott A exposed to sub-lethal concentrations of natural antimicrobials

Abstract

One of the emerging strategies proposed to prevent the presence and the growth of Listeria monocytogenes in food products is the use of natural antimicrobial compounds like essential oils (EOs) or their components alone or in combination with other mild hurdles. The aim of this study was to explore the gene expression mechanisms of L. monocytogenes Scott A exposed for 1 h to different sub-lethal antimicrobial concentrations of (E)-2-hexenal, citral, carvarcol and thyme EO in order to understand the impact of these molecules on the main metabolic pathways of this pathogenic strain. RT-qPCR has been performed on L. monocytogenes cells exposed to the target antimicrobials. The presence of the antimicrobials induced a clear unbalance in the catabolic processes, suggesting a shift from oxidation to fermentation metabolism (pdhD, pgm). Moreover, the results highlighted how antimicrobials belonged to the same chemical class induced different stress response mechanisms on L. monocytogenes Scott A. The information about the cell responses to the exposure to the natural antimicrobials selected is crucial to understand which cell target(s) can be affected, and consequently how the inhibition of pathogens survival can be further enhanced.

Keywords: Essential oils; Listeria monocytogenes; Natural antimicrobials; RT-qPCR; Stress response.