Antibacterial Mode of Action of the Essential Oil Obtained from Chamaecyparis obtusa Sawdust on the Membrane Integrity of Selected Foodborne Pathogens

The present study examines the possible antibacterial mechanism of action of the essential oil obtained from Chamaecyparis obtusa (COEO) sawdust against foodborne pathogenic bacteria. The COEO was obtained by microwave-assisted hydrodistillation of C. obtusa sawdust. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of COEO against the tested foodborne pathogens including Bacillus cereus ATCC 13061, Listeria monocytogenes ATCC 7644, Staphylococcus aureus ATCC 12600, Salmonella Typhimurium ATCC 43174 and Escherichia coli ATCC 43889 were found in the range from 62.5 to 500 mg/mL and from 125 to 1000 mg/mL, respectively. At the MIC concentrations, the COEO had potential inhibitory effect on the cell viability of the tested bacteria. In addition, the scanning electron microscopic analysis confirmed the inhibitory effect of COEO by revealing significant morphological alterations or rupture of the cell membranes of B. cereus ATCC 13061 and E. coli ATCC 43889. Moreover, the mode of action of COEO on the cell membrane of both Gram-positive B. cereus ATCC 13061 and Gram-negative E. coli ATCC 43889 bacteria was confirmed by marked release of extracellular adenosine 5’-triphosphate (ATP) and cellular material that absorbs at 260 nm, and by efflux of potassium ions. These findings suggest that COEO holds a broad-spectrum antibacterial efficacy, confirming its influence on the membrane integrity and morphological characteristics of tested foodborne pathogens.