The in vitro antibiofilm activity of selected culinary herbs and medicinal plants against Listeria monocytogenes

Aims: The antibiofilm activity of extracts obtained from selected herbs, spices, beverages and commercially important medicinal plants was investigated on Listeria monocytogenes. Methods and Results: The growth and development of the biofilm was assessed using the crystal violet (CV) assay. The respiratory activity was assessed using the 2, 3-bis [2-methyloxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxanilide (XTT) reduction assay. The majority of extracts tested prevented cell adhesion to the polyvinyl chloride (PVC) surface. Seven of the 15 extracts reduced biofilm adhesion of both the clinical and the type strains by at least 50%. In contrast, inhibition of a preformed biofilm was more difficult to achieve, with only three extracts (Rosmarinus officinalis, Mentha piperita and Melaleuca alternifolia) inhibiting the growth of both strains by at least 50%. Conclusions: Although most extracts were able to reduce initial cell attachment, inhibition of growth in a preformed biofilm was more difficult to achieve. Significance and Impact of the Study: The ability to reduce biofilm biomass as shown by several plant extracts warrants further investigation to explore the use of natural products in antibiofilm adhesion.