Extensive documentation on the antimicrobial properties of essential oils and their constituents has been carried out by several workers. Although the mechanism of action of a few essential oil components has been elucidated in many pioneering works in the past, detailed knowledge of most of the compounds and their mechanism of action is still lacking. This knowledge is particularly important for the determination of the effect of essential oils on different microorganisms, how they work in combination with other antimicrobial compounds, and their interaction with food matrix components. Also, recent studies have demonstrated that nanoparticles (NPs) functionalized with essential oils have significant antimicrobial potential against multidrug- resistant pathogens due to an increase in chemical stability and solubility, decreased rapid evaporation and minimized degradation of active essential oil components. The application of encapsulated essential oils also supports their controlled and sustained release, which enhances their bioavailability and efficacy against multidrug-resistant pathogens. In the recent years, due to increasingly negative consumer perceptions of synthetic preservatives, interest in essential oils and their application in food preservation has been amplified. Moreover, the development of resistance to different antimicrobial agents by bacteria, fungi, viruses, parasites, etc. is a great challenge to the medical field for treating the infections caused by them, and hence, there is a pressing need to look for new and novel antimicrobials. To overcome these problems, nano-encapsulation of essential oils and exploiting the synergies between essential oils, constituents of essential oils, and antibiotics along with essential oils have been recommended as an answer to this problem. However, less is known about the interactions that lead to additive, synergistic, or antagonistic effects. A contributing role of this knowledge could be the design of new and more potent antimicrobial blends, and understanding of the interplay between the components of crude essential oils. This review is written with the purpose of giving an overview of current knowledge about the antimicrobial properties of essential oils and their mechanisms of action, components of essential oils, nano-encapsulated essential oils, and synergistic combinations of essential oils so as to find research areas that can facilitate applications of essential oils to overcome the problem of multidrug-resistant micro-organisms.

Antimicrobial Activity of Some Essential Oils-Present Status and Future Perspectives.

A wide range of medicinal and aromatic plants (MAPs) have been explored for their essential oils in the past few decades. Essential oils are complex volatile compounds, synthesized naturally in different plant parts during the process of secondary metabolism. Essential oils have great potential in the field of biomedicine as they effectively destroy several bacterial, fungal, and viral pathogens. The presence of different types of aldehydes, phenolics, terpenes, and other antimicrobial compounds means that the essential oils are effective against a diverse range of pathogens. The reactivity of essential oil depends upon the nature, composition, and orientation of its functional groups. The aim of this article is to review the antimicrobial potential of essential oils secreted from MAPs and their possible mechanisms of action against human pathogens. This comprehensive review will benefit researchers who wish to explore the potential of essential oils in the development of novel broad-spectrum key molecules against a broad range of drug-resistant pathogenic microbes.

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Antimicrobial Properties of Plant Essential Oils against Human Pathogens and Their Mode of Action: An Updated Review.

Nanoencapsulation of hydrophobic and low-soluble food bioactive compounds within different nanocarriers

Starch-PVA composite films with zinc-oxide nanoparticles and phytochemicals as intelligent pH sensing wraps for food packaging application.

Antimicrobial and antioxidant activity of unencapsulated and encapsulated clove (Syzygium aromaticum, L.) essential oil.

The specific antibacterial activity of liposome-encapsulated Clove oil and its application in tofu

Nowadays, essential oils are recognized as safe substances and can be used as antibacterial additives. Salvia sclarea is one of the most important aromatic plants cultivated world-wide as a source of essential oils. In addition to being flavoring foods, Salvia sclarea essential oil can also act as antimicrobials and preservatives against food spoilage. Understanding more about the antibacterial performance and possible mechanism of Salvia sclarea essential oil will be helpful for its application in the future. But so far few related researches have been reported. In our study, Salvia sclarea oil showed obvious antibacterial activity against all tested bacterial strains. Minimum inhibitory concentration (MIC) and minimum bactericide concentration (MBC) of seven pathogens were 0.05 and 0.1 % respectively. In addition, Salvia sclarea oil also exhibited a significant inhibitory effect on the growth of Escherichia coli (E. coli) in phosphate buffer saline (PBS) and meats. After treated with Salvia sclarea oil, Scanning Electron Microscope (SEM) images can clearly see the damage of cell membrane; the intracellular ATP concentrations of E. coli and S. aureus reduced 98.27 and 69.61 % respectively, compared to the control groups; the nuclear DNA content of E. coli and S. aureus was significantly reduced to 48.32 and 50.77 % respectively. In addition, there was massive leakage of cellular material when E. coli and S. aureus were exposed to Salvia sclarea oil. Salvia sclarea essential oil damaged the cell membrane and changed the cell membrane permeability, leading to the release of some cytoplasm such as macromolecular substances, ATP and DNA. In general, the antimicrobial action of Salvia sclarea essential oil is not only attributable to a unique pathway, but also involves a series of events both on the cell surface and within the cytoplasm. Therefore, more experiments need to be done to fully understand the antimicrobial mechanism of Salvia sclarea essential oil.

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Antimicrobial activity and mechanisms of Salvia sclarea essential oil

In this study, the antibacterial activities of nutmeg oil and nutmeg oil encapsulated in liposome were evaluated. First, nutmeg oil exhibited a significant antibacterial effect on L. monocytogenes by damaging the integrity of the cell membrane, leading to the leakage of ATP and nucleic acid. Subsequently, nutmeg oil was encapsulated in liposome to enhance its chemical stability using a thin film dispersion method. The optimal Zeta potential (−49.2 mV) and entrapment efficiency (26.90%) of liposome were achieved at 5.0 mg mL−1 nutmeg oil encapsulation. Finally, the selective antibacterial activity for L. monocytogenes using pore-forming toxins (PFTs) to trigger the release of nutmeg oil from liposome was examined by time-kill analysis and gas chromatography (GC). The long-term antibacterial activity test showed that nutmeg oil encapsulated in liposome could extend the treatment time and improve the antibacterial effect on L. monocytogenes in dumplings.

Liposome containing nutmeg oil as the targeted preservative against Listeria monocytogenes in dumplings

In the present paper, the chemical composition of Helichrysum italicum oil was analyzed by gas chromatography–mass spectrometry (GC-MS). Neryl acetate (32.65%) was the main component. The minimum inhibitory concentration and minimum bactericidal concentration of H. italicum oil against several bacteria were evaluated. The results showed that H. italicum oil exhibited high antibacterial activity against all of the bacteria tested. In addition, H. italicum oil also displayed a significant effect on inhibiting the growth rate of surviving Escherichia coli and Staphylococcus aureus in vitro and on vegetables. Meanwhile, addition of H. italicum oil to vegetable exerted a bacteriostatic effect. Besides, the mechanisms of the antimicrobial action of H. italicum oil to E. coli and S. aureus were concluded as that H. italicum oil could disrupt the cell membrane integrity, leading to the losses of intracellular constituents, such as the 260 nm absorbing materials, DNA and ATP.



Practical Applications

As a kind of natural, safe spice, Helichrysum italicum oil has been proven to be a good antibacterial agent against a wide range of bacteria at a low concentration and short incubation time. Especially, H. italicum oil exhibits a significant bacteriostatic effect in vegetables. Based on the results, we believe that H. italicum oil can be applied in vegetable processing and preservation.

Antibacterial Activity of Helichrysum italicum Oil on Vegetables and Its Mechanism of Action

The aim of this study is to investigate the antibacterial characteristics and mechanisms of nutmeg oil. In this paper, 54 chemical compositions of nutmeg oil were analyzed by gas chromatography–mass spectrometry (GC–MS). The major volatile components of nutmeg oil were sabinene (39.12%) and alpha-pinene (11.96%). In addition, nutmeg oil showed significant antibacterial activity, minimum inhibitory concentration, and minimum bactericide concentration of seven pathogens are 0.05 and 0.1%, respectively, and the nutmeg oil also had a significant effect on inhibiting the growth of Escherichia coli and Staphyloccocus aureus in phosphate buffer saline and pork. Subsequently, in order to reveal the possible antibacterial mechanisms of nutmeg oil against pathogens, the damage of cell membrane was observed by scanning electron microscopy, the loss of 260 nm absorbing material was tested by ultraviolet spectrophotometer, and the cellular adenosine triphosphate concentrations were measured by the Surface Hygiene Test Kit. Finally, the decrease of nucleic acid was evaluated by inverted fluorescence microscope. These results indicated that the antibacterial mechanisms of the nutmeg oil against bacteria might be interpreted as disrupting cell membrane and inhibiting synthesis of DNA.



Practical Applications

As a natural and safe antibacterial agent, nutmeg oil exhibited good antimicrobial activity against a wide range of spoilage and pathogenic bacteria. Meanwhile, the antimicrobial activity of nutmeg oil has been proved on pork. Based on the results, we believe that nutmeg oil can be applied in meat storage and preservation.

Chengting Zhao

Papers

The specific antibacterial activity of liposome-encapsulated Clove oil and its application in tofu

Antimicrobial activity and mechanisms of Salvia sclarea essential oil

Liposome containing nutmeg oil as the targeted preservative against Listeria monocytogenes in dumplings

Antibacterial Activity of Helichrysum italicum Oil on Vegetables and Its Mechanism of Action

Antibacterial Properties of Nutmeg Oil in Pork and Its Possible Mechanism