Control of planktonic and sessile bacterial cells by essential oils

The antibacterial potential of essential oils (EOs) from Cinnamomum cassia bark and Melaleuca alternifolia and Cymbopogon flexuosus leaves was evaluated against planktonic and sessile cells of enteropathogenic Escherichia coli (EPEC) and Listeria monocytogenes. The EOs were tested singly and in different combinations of equal percentages: mixtures of two (1:1 in v/v) and three EOs (1:1:1 in v/v/v). The minimal inhibitory concentrations (MICs) were determined against planktonic cells and the anti-biofilm activity was verified against bacterial cells adhered in the wells of polystyrene microplates. These initial tests indicated the EO of C. cassia as a potential anti-biofilm agent, and their effect was studied against sessile cells of biofilms formed on stainless steel surface under agitation and static conditions. For both bacterial species, a solution containing 2% (v/v) of C. cassia EO was effective against the biofilm formed under static conditions, because the counts obtained were below the detection level of the plate count method employed. Although the biofilm of L. monocytogenes showed a decreased number of adhered cells after formation under agitating conditions (p<0.05), it was surprisingly more resistant to the EO of C. cassia than the biofilm formed under static conditions (p<0.05). All of the EOs and combinations tested presented antibacterial activity, almost against planktonic cells; however, the EO of C. cassia showed to be the most effective as a potential agent for the production of sanitizers for biofilm control in the food industries. (C) 2012 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.