Antimicrobial Activity of Some Plant Essential Oils Against Listeria monocytogenes1

Abstract

The antimicrobial activity of 32 plant essential oils commonly used in food industry was examined against four strains of Listeria monocytogenes and one strain of Listeria innocua. Two different procedures were carried out to test the essential oils, a paper disc diffusion method and an inhibition curve. In the former procedure an absolute ethanolic solution (1:5 v/v) of each oil was tested on the plates inoculated with a bacterial concentration of 106 CFU/ml. Five of the 32 essential oils (cinnamon, clove, origanum, pimento, and thyme) showed antibacterial activity. Some of the five oils were also tested at lower concentration (1:50 v/v). The inhibition curve to study antilisteric efficacies of the five oils in a saline solution system was examined. Pimento oil showed marked and rapid activity (generally within 1 h of exposure), whereas clove, origanum, and thyme oils showed a more slow activity. The antilisteric activity of the tested oils seems to be strain dependent. A L. monocytogenes strain was also tested in a food matrix (minced pork meat) against thyme essential oil. Minced pork meat with thyme oil reduced the L. monocytogenes population by ca. 100-fold over the first week of storage.