CHARACTERIZATION OF THE ACTION OF SELECTED ESSENTIAL OIL COMPONENTS ON GRAM-NEGATIVE BACTERIA

Carvacrol, (+)-carvone, thymol, and trans-cinnamaldehyde were tested f or their inhibitory activity against Escherichia coli O157:H7 and Salm onella typhimurium. In addition, their toxicity to Photobacterium leio gnathi was determined, utilizing a bioluminescence assay. Their effect s on the cell surface were investigated by measuring the uptake of 1-N -phenylnaphthylamine (NPN), by measuring their sensitization of bacter ial suspensions toward detergents and lysozyme, and by analyzing mater ial released from cells upon treatment by these agents. Carvacrol, thy mol, and trans-cinnamaldehyde inhibited E. coli and S. typhimurium at 1-3 mM, whereas (+)-carvone was less inhibitory. trans-Cinnamaldehyde was the most inhibitory component toward P. leiognathi. Carvacrol and thymol disintegrated the outer membrane and released outer membrane-as sociated material from the cells to the external medium; such release by (+)-carvone or trans-cinnamaldehyde was negligible. Of the tested c omponents, carvacrol and thymol decreased the intracellular ATP pool o ff. coli and also increased extracellular ATP, indicating disruptive a ction on the cytoplasmic membrane.