Homologous and heterologous adaptation of Listeria spp. to essential oils of condiment plants

Abstract

The homologous and heterologous adaptation capacity of L. monocytogenes and L. innocua were determined for thyme, oregano and nutmeg essential oils, as well as their adaptation capacities to acidic stress. Minimum bactericidal concentrations (CMB) and minimum inhibitory and minimum growth pH, were established. The capacity for increased tolerance to essential oils and acidic stress, along with heterologous adaptation among the essential oils tested and to acidic pH was determined, and that between pH and essential oils. L. monocytogenes and L. innocua adapted to all essential oils and to the minimum inhibitory pH, after exposition to sub-lethal conditions. Both strains presented heterologous adaptation capacity. After previous exposition to sub-lethal essential oil concentrations, the regenerated cells were capable of growth under 3.5 pH values, and increased CMB values. Essential oil CMBs for previously cultivated cells under minimum growth pH environments also increased, attaining values 1.6 times superior to previous ones.