Inhibitory activity of yarrow essential oil on Listeria planktonic cells and biofilms

The inhibitory effects of the essential oil obtained from yarrow (Achillea millefolium) were tested against planktonic cells and biofilms of Listeria monocytogenes and Listeria innocua isolates obtained from food processing environments. The plant essential oil was found to have strong bactericidal activity against planktonic cells which was found to be equivalent to that of tea tree oil (Melaleuca alternifolia). Inhibition of biofilm formation and growth after incubation with different concentrations of yarrow essential oil was assessed by the crystal violet and 3-[4, 5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide reduction assay. Yarrow essential oil significantly inhibited the initial cell attachment of the Listeria cells on polystyrene, stainless steel and high density polyethylene surfaces but was less inhibitory towards 6 h preformed biofilms formed on polystyrene surface. Metabolic activity of the biofilms decreased considerably after incubation with the oil. Yarrow essential oil, or its constituents, may be useful additives for the development of new disinfectant and sanitizer formulations for application in the food industry.