Mechanisms of Action of Carvacrol on the Food-Borne Pathogen Bacillus cereus

Carvacrol, a naturally occurring compound mainly present in the essential oil fraction of oregano and thyme, was studied for its effect on bioenergetic parameters of vegetative cells of the food-borne pathogen Bacillus cereus. Incubation for 30 min in the presence of 1 to 3 mM carvacrol reduced the viable cell numbers exponentially. Carvacrol (2 mM) significantly depleted the intracellular ATP pool to values close to 0 within 7 min. No proportional increase of the extracellular ATP pool was observed. Depletion of the internal ATP pool was associated with a change of the membrane potential (Deltapsi). At concentrations of 0.01 mM carvacrol and above, a significant reduction of Deltapsi was observed, leading to full dissipation of Deltapsi at concentrations of 0.15 mM and higher. Finally, an increase of the permeability of the cytoplasmic membrane for protons and potassium ions was observed (at 0.25 and 1 mM carvacrol, respectively). From this study, it could be concluded that carvacrol interacts with the membranes of B. cereus by changing its permeability for cations like H(+) and K(+). The dissipation of ion gradients leads to impairment of essential processes in the cell and finally to cell death.