Evaluation of antibacterial effect of Rosmarinus officinalis L. essential oil on three food-borne pathogens in vegetables by propidium monoazide quantitative PCR

Essential oils (EOs) have long been applied as flavoring agents in foods. Nowadays, due to the antimicrobial properties of EOs, they have been used as natural food preservatives. In this study, initial experiments were performed in order to elucidate the minimum bactericidal concentration of Rosmarinus officinalis L.EO on Escherichia coli O157:H7, Salmonella enterica and Listeria monocytogenes. Thereafter, PMA-qPCR was applied in order to selectively quantify living cells within a bacterial population treated with rosemary EO. Inactivation was obtained at EO concentrations of 1%, 0.45%, 0.9% for L. monocytogenes, E. coli O157:H7 and S. enterica, respectively. L. monocytogenes were totally killed within 45 min while it took 90 min for E. coli O157:H7and S. enterica. It was concluded that rosemary EO has the potential to be used as a natural food additive or bio-preservative since it was able to irreversibly inactivate the three tested pathogens at lower concentrations and short exposition times in comparison with the other EOs. In addition, PMA-qPCR approach proved quantitatively precise and specific to selectively detect live pathogenic bacteria in vegetables following inactivation with rosemary EO.