Plant oils as antibacterial agents

Essential oils of herbs and spices and their components, such as eugenol, carvacrol and cinnamaldehyde, are active as antimicrobials against a wide range of Gram negative and positive bacteria. These agents have potential as antimicrobials for use in food products. The mechanism of action of these agents is poorly understood. The development of effective antimicrobial treatments based on essential oils requires an understanding of their mechanism of action.; The potential of cilantro oil to control the growth of Listeria monocytogenes on vacuum packed ham was investigated. Cilantro oil is an essential oil preparation extracted from the plant Coriandrum sativum.; The only treatment that inhibited growth of L. monocytogenes was the 6% cilantro oil gel. Samples receiving this treatment had populations of L. monocytogenes 1.3 log CFU/ml lower than controls at week one of storage, though there was no difference between treatments from week two onward. Immobilization of the antimicrobial in a gel appeared to enhance the effectiveness of treatments.; To investigate the role of interference with energy generation in the mechanism of action, the cellular and extracellular ATP of cells in HEPES buffer at 20°C were measured. Treatment of non-energised L. monocytogenes with 5 mM eugenol, 40 mM cinnamaldehyde or 10 muM carbonyl cyanide m-chlorophenylhydrazone (CCCP) for 5 min prevented an increase in cellular ATP upon addition of glucose. Treatment of energised L. monocytogenes with 40 mM cinnamaldehyde or 10 muM CCCP caused a rapid decline in cellular ATP levels, but 5 mM eugenol had no effect on cellular ATP. Treatment of Lb. sakei with 10 mM eugenol prevented ATP generation by non-energised cells, and had no effect on the cellular ATP of energised cells. CCCP at 100 muM had no significant effects on the cellular ATP of Lb. sakei. Due to their rapidity, effects on energy generation clearly play a major role in the activity of eugenol and cinnamaldehyde at bactericidal concentration.; The results of these experiments indicate that eugenol and carvacrol cause cell death by disrupting the cellular membrane leading to leakage of cell contents. Disruptive membrane interactions are less clearly indicated for cinnamaldehyde. The antimicrobials also inhibited membrane associated ATPase activity. ATPase inhibition may be a secondary mechanism in cell death, resulting from non-specific hydrophobic interactions of the molecules with membrane bound enzymes. (Abstract shortened by UMI.)...