Interstrains comparison of the antimicrobial effect and mode of action of a Vietnamese Cinnamomum cassia essential oil from leaves and its principal component against Listeria monocytogenes

The antibacterial activity of a Cinnamomum cassia essential oil (EO) and of its main component trans ‐cinnamaldehyde (90% w/w) was examined against five Listeria monocytogenes strains. The minimal inhibitory concentrations (MICs) of C .  cassia EO against the five L .  monocytogenes strains were identical (250  µ g ml −1 ), while the minimal bactericidal concentrations (MBCs) ranged between 800 and 1200  µ g ml −1 . In order to study if this EO and trans ‐cinnamaldehyde altered the five strains at the membrane level, fluorescence anisotropy of 1,6‐diphenyl‐1,3,5‐hexatriene (DPH) was measured in presence of different concentrations (1/2MIC, MIC, 2MIC) of these antibacterial agents. A concentration‐dependent increase of fluorescence anisotropy of DPH in their presence reflecting a rigidification of the membrane was observed for the five strains. This modification of the membrane fluidity was associated with a perturbation of the selective membrane permeability, as a perturbation of the gradient between intracellular and extracellular pH was also observed.