title: Mechanism of action of Spanish oregano, Chinese cinnamon, and savory essential oils against cell membranes and walls of Escherichia coli O157:H7 and Listeria monocytogenes.
abstract: The mechanism of the antimicrobial action of Spanish oregano (Corydothymus capitatus), Chinese cinnamon (Cinnamomum cassia), and savory (Satureja montana) essential oils against cell membranes and walls of bacteria was studied by the measurement of the intracellular pH and ATP concentration, the release of cell constituents, and the electronic microscopy observations of the cells when these essential oils at their MICs were in contact with Escherichia coli O157:H7 and Listeria monocytogenes. E. coli O157:H7 and L. monocytogenes, two pathogenic foodborne bacteria, were used as gram-negative and gram-positive bacterial models, respectively. Treatment with these essential oils at their MICs affected the membrane integrity of bacteria and induced depletion of the intracellular ATP concentration. Spanish oregano and savory essential oils, however, induced more depletion than Chinese cinnamon oil. An increase of the extracellular ATP concentration was observed only when Spanish oregano and savory oils were in contact with E. coli O157:H7 and L. monocytogenes. Also, a significantly higher (P < or = 0.05) cell constituent release was observed in the supernatant when E. coli O157:H7 and L. monocytogenes cells were treated with Chinese cinnamon and Spanish oregano oils. Chinese cinnamon oil was more effective to reduce significantly the intracellular pH of E. coli O157:H7, whereas Chinese cinnamon and Spanish oregano decreased more significantly the intracellular pH of L. monocytogenes. Electronic microscopy observations revealed that the cell membrane of both treated bacteria was significantly damaged. These results suggest that the cytoplasmic membrane is involved in the toxic action of essential oils.
authors.affiliation: Canadian Irradiation Center and Research Laboratory in Sciences Applied to Food, Institut Nacional de la Recherche Scientifique, Institut Armand-Frappier, Université du Québec, 531 Boulevard des Prairies, Laval, Québec, Canada.
authors.forename: Mounia
authors.initials: M
authors.lastname: Oussalah
authors.forename: Stéphane
authors.initials: S
authors.lastname: Caillet
authors.forename: Monique
authors.initials: M
authors.lastname: Lacroix
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000648:ultrastructure; D002935:Cinnamomum zeylanicum / Q000737:chemistry; D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D019453:Escherichia coli O157 / Q000187:drug effects* / Q000254:growth & development / Q000648:ultrastructure; D005511:Food Handling / Q000379:methods; D005516:Food Microbiology; D005519:Food Preservation / Q000379:methods*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008089:Listeria monocytogenes / Q000187:drug effects* / Q000254:growth & development / Q000648:ultrastructure; D008826:Microbial Sensitivity Tests; D008854:Microscopy, Electron / Q000379:methods; D009822:Oils, Volatile / Q000494:pharmacology*; D031341:Origanum / Q000737:chemistry; D031362:Satureja / Q000737:chemistry; D013997:Time Factors
chemical_list: D009822:Oils, Volatile; D000255:Adenosine Triphosphate