Functional and ultrastructural changes in Pseudomonas aeruginosa and Staphylococcus aureus cells induced by Cinnamomum verum essential oil.

AIMS: To study cellular damage induced by Cinnamomum verum essential oil in Pseudomonas aeruginosa ATCC 27853 and Staphylococcus aureus ATCC 29213. METHODS AND RESULTS: The effect of cinnamon bark essential oil on these two strains was evaluated by plate counts, potassium leakage, flow cytometry and transmission electron microscopy (TEM). Exposure to this oil induced alterations in the bacterial membrane of Ps. aeruginosa, which led to the collapse of membrane potential, as demonstrated by bis-oxonol staining, and loss of membrane-selective permeability, as indicated by efflux of K(+) and propidium iodide accumulation. Thus, respiratory activity was inhibited, leading to cell death. In Staph. aureus, cells treated with the oil entered a viable but noncultivable (VNC) state. The oil initially caused a considerable decrease in the metabolic activity and in the replication capacity of these bacterial cells. The loss of membrane integrity appeared later, as indicated by bis-oxonol and Propidium iodide (PI) staining. Data provided by TEM showed various structural effects in response to cinnamon essential oil. In Ps. aeruginosa cells, coagulated cytoplasmic material was observed, and intracellular material was seen in the surrounding environment, while oil-treated Staph. aureus showed fibres extending from the cell surface. CONCLUSIONS: Cinnamon essential oil damages the cellular membrane of Ps. aeruginosa, which leads to cell death. There is evidence of VNC Staph. aureus after exposure to the oil. SIGNIFICANCE AND IMPACT OF THE STUDY: Cinnamon essential oil shows effective antimicrobial activity and health benefits and is therefore considered a potential food additive. To use this oil as a natural food preservative, especially in combination with other preservation methods, a thorough understanding of the mechanism through which this oil exerts its antibacterial action is required.

Investigation of functional and morphological changes in Pseudomonas aeruginosa and Staphylococcus aureus cells induced by Origanum compactum essential oil.

AIMS: Evaluation of the cellular effects of Origanum compactum essential oil on Pseudomonas aeruginosa ATCC 27853 and Staphylococcus aureus ATCC 29213. METHODS AND RESULTS: The damage induced by O. compactum essential oil on these two strains has been studied using different techniques: plate count, potassium leakage, flow cytometry (FC) and transmission electron microscopy (TEM). The results showed that oil treatment led to reduction of cells viability and dissipated potassium ion gradients. Flow cytometric analysis showed that oil treatment promoted the accumulation of bis-oxonol and the membrane-impermeable nucleic acid stain propidium iodide (PI), indicating the loss of membrane potential and permeability. The ability to reduce 5-cyano-2,3-ditolyl tetrazolium chloride was inhibited. Unlike in Ps. aeruginosa, membrane potential and membrane permeability in Staph. aureus cells were affected by oil concentration and contact time. Finally, TEM showed various structural effects. Mesosome-like structures were seen in oil-treated Staph. aureus cells whereas in Ps. aeruginosa, coagulated cytoplasmic material and liberation of membrane vesicles were observed, and intracellular material was seen in the surrounding environment. Both FC and TEM revealed that the effects in Ps. aeruginosa were greater than in Staph. aureus. CONCLUSIONS: Oregano essential oil induces membrane damage showed by the leakage of potassium and uptake of PI and bis-oxonol. Ultrastructural alterations and the loss of cell viability were observed. SIGNIFICANCE AND IMPACT OF THE STUDY: Understanding the mode of antibacterial effect of the oil studied is of a great interest in it further application as natural preservative in food or pharmaceutical industries.