Single and binary applications of essential oils effectively control Listeria monocytogenes biofilms

The high environmental impact and the increasing resistance of microorganisms to conventional disinfectants applied in the food industry have led to an increasing interest in the antimicrobial properties of plant essential oils (EOs). The present study aimed to develop highly effective EO-based treatments against Listeria monocytogenes biofilms formed on stainless steel and polystyrene surfaces under food-related conditions. EOs with an efficacy comparatively higher or similar to peracetic acid and sodium hypochlorite against L. monocytogenes planktonic cells were selected, including for the first time Cordia verbenacea and Pimenta pseudochariophyllus oils. Selected EOs were subsequently characterized chemically by GC/MS analysis and applied in single treatments, binary combinations and combinations with peracetic acid to evaluate their efficacy against 24-h-old L monocytogenes biofilms. Lippia sidoides, Thymus vulgaris and Pimento pseudochariophyllus oils were highly effective against planktonic cells and biofilms of L. monocytogenes. Thymol was the main compound of Lippia sidoides and Thymus vulgaris oils, whereas Pimento pseudochariophyllus contained high concentrations of chavibetol. However, only Lippia sidoides oil was able to completely eradicate L. monocytogenes biofihns at relatively high doses (2.75% v/v). The application of selected EOs in binary combinations decreased considerably doses required to kill 99.99% of biofilm cells. Moreover, the application of peracetic acid combined with these EOs enhanced its efficacy against L. monocytogenes biofilms. Therefore, EO-based treatments proposed in this study, particularly those combining L. sidoides with T. vulgaris or peracetic acid, could represent an effective and environmentally friendly strategy to control L. monocytogenes biofilms in food-processing environments. (AU)