CHANGES IN LISTERIA MONOCYTOGENES INDUCED BY ORIGANUM VULGARE L. and ROSMARINUS OFFICINALIS L. ESSENTIAL OILS ALONE AND COMBINED AT SUBINHIBITORY AMOUNTS

ABSTRACT This study aimed to evaluate the antibacterial activities of the essential oils from Origanum vulgare L. and Rosmarinus officinalis L., both singly and in combination at subinhibitory concentrations against Listeria monocytogenes, and to investigate the possible mechanisms underlying these activities. Used singly or in a mixture, the essential oils led to a significant decrease in cell viability during 24 h of exposure. Decreased glucose consumption and the loss of cellular material by L. monocytogenes were found immediately after addition of the essential oils alone and in combination, and continued for up to 360 min. Analysis of cells exposed to the essential oils using electron microscopy revealed drastic ultrastructural changes occurring over time, including the changes in cell wall structure, rupture of plasma membranes, shrinking of the cytoplasmic content and leakage of intracellular material. O. vulgare L. and R. officinalis L. essential oils combined at subinhibitory concentrations could be rationally applied to inhibit the growth of L. monocytogenes in food products. PRACTICAL APPLICATIONS L. monocytogenes is a foodborne pathogen of particular concern in ready‐to‐eat products, such as minimally processed vegetables, because of its ability to survive and grow at refrigeration temperatures. The special risk posed by L. monocytogenes for the consumption of minimally processed vegetables has led to investigations on the development of novel technologies to control this contamination. In this context, plant essential oils have received particular interest for their potential to control L. monocytogenes in these foods. The findings of our study clearly indicate that the essential oil of oregano and rosemary, singly or in combination at subinhibitory concentrations, caused critical damages in L. monocytogenes cells. These essential oils combined at subinhibitory concentrations could be rationally applied to control the survival of L. monocytogenes in foods.