Testing the antimicrobial activity of essential oils

Foods

A novel alternative to synthetic preservatives is the use of natural products such as essential oil (EO) as a natural food-grade preservative. EOs are Generally Recognized as Safe (GRAS), so they could be considered an alternative way to increase the shelf-life of highly perishable food products by impeding the proliferation of food-borne pathogens. The mounting interest within the food industry and consumer preference for “natural” and “safe” products means that scientific evidence on plant-derived essential oils (EOs) needs to be examined in-depth, including the underlying mechanisms of action. Understanding the mechanism of action that individual components of EO exert on the cell is imperative to design strategies to eradicate food-borne pathogens. Results from published works showed that most EOs are more active against Gram-positive bacteria than Gram-negative bacteria due to the difference in the cell wall structure. In addition, the application of EOs at a commercial scale h...

Applied Sciences, 2020

Due to the increasing risk of chemical contaminations in the application of synthetic fungicides, the use of plant essential oils and extracts has recently been increased. In the present review, the antimicrobial potential of the most active plant-food essential oils in liquid and vapor phases has been reviewed. The volatile isothiocyanates, aldehydes, and phenols, including allyl isothiocyanate, carvacrol, thymol, and eugenol, are considered to be the predominant components of essential oils, possessing significant antimicrobial activities. These components alone or in mixture can be effective. Overall, the antimicrobial activity of aroma compounds depends on the plant species, concentration, and method of application. This review provides useful information about the inhibitory application of the most common plant-foods’ essential oils in liquid and vapor phases against the growth of pathogenic microorganisms. Essential oils (EOs) are promising natural antimicrobial alternatives i...

African Journal of …, 2010

The aim of the present study was to assess the effect of extrinsic factors on the antimicrobial effectiveness of essential oils (EOs) against medically important gram positive and gram negative bacteria. Clove, oregano, bay and cinnamon essential oils were tested against Salmonella typhimurium, Escherichia coli, Bacillus cereus and Listeria innocua. Agar diffusion test was used to estimate the strength of the essential oil. Clove was most effective against all groups of bacteria. The minimum inhibition concentrations (MIC) of the four essential oils ranged from 1.25 to 3.50% (v/v) as determined by turbidimetric technique using Biocreen C, analyzer. In order to test the combined effect of pH, sodium chloride, temperature and EOs on the growth of bacteria, the concentrations of the EOs were set at 0.03125% (v/v) below MICs. A synergistic effect against the test bacteria was achieved at the concentration 1.2% (w/v) NaCl and either oregano or clove oil (P < 0.01), however clove was bactericidal on both classes of bacteria at 37°C, pH 5.5 and in combination with NaCl at 1.8% (w/v) pH (7.3), suggesting that EOs can be combined with NaCl at low concentrations overcome organoleptic effects in food and inhibit growth of pathogenic bacteria.

World Journal of Pharmaceutical Research, 2017

Medicinal plants and their essential oils have been used for centuries in traditional system of medicine and they have been appreciated for multiple effects against a variety of infections. Bacterial infections and their complications are presently regarded as the most difficult and expensive to treat. Though the discovery of antibiotics has proven to be a major asset against bacteria, the extensive use of antibiotics since recent days has led to the emerging increase in resistant strains of bacteria. Therefore the present millennium is in search of safe and natural drugs to tackle these common pathogens and to prevent the optimum increase in mortality rates due to multi drug resistant bacteria. The purpose of this research was to estimate the antibacterial effect of the formulated essential oil against common and selected pathogens E.coli, Proteus mirabilis, Staphylococcus aureus and Vibrio cholera by means of Disc diffusion assay and Agar vapour assay. The zone of inhibition was compared in both states of direct contact and vapour phase methods at the concentrations of 10, 15, 20 and 25 micro litre/ml against the selected pathogens. The results were statistically analysed by paired T test and P Value <0.05 for Proteus mirabilis, Staphylococcus aureus and Vibrio cholera indicated that the formulated essential oil showed antimicrobial activity against both gram positive and gram negative bacteria. The formulation also portrayed considerable antimicrobial effect at vapour phase (25 micro litre/ml) than by direct contact method.

Madridge Journal of Food Technology, 2019

This paper is a review of essential oils and their use in foods, packaging materials and farm animals. Essential oils are aromatic oil liquids obtained from plant materials. They serve crucial roles as antioxidants, pathogen inhibitors and flavoring agents. Because of label appearance concerns, essential oils are increasingly used as food preservatives. Essential oils have a complex composition and properties that vary based on differences in field growth, postharvest and processing conditions. Chemical and physical properties of essential oils affect their ability to act as antimicrobials. The food matrix has a significant impact on the antibacterial properties of essential oils, based on factors like pH, fat and moisture content. Meat products have experienced broad application of essential oils as preservatives, while fish and seafood have seen limited use. Essential oils have been used to clean and preserve vegetables, rice and fruits. Food coatings and packaging materials have been treated with essential oils to enhance food preservation properties. Many factors influence the activity of essential oils in foods including synergism (vacuum packaging, pH, water activity, other preservatives and sodium chloride), antagonism (composition of food and sodium chloride) and additive effects. Many essential oils are regarded as safe, but under certain conditions, they may cause dermatitis and cytotoxicity. Challenges to the expanding use of essential oils as antimicrobials in the food industry include organoleptics, uniformity of composition, and emerging resistance of microbes.

2017

The aim of this study was to optimize the antimicrobial efficacy of plant essential oils (EO's) for control of Listeria spp. and spoilage bacteria using food model media based on lettuce, meat and milk. The EO's evaluated were lemon balm, marjoram, oregano and thyme and their minimum inhibitory concentrations (MIC) were determined against Enterobacter spp., Listeria spp., Lactobacillus spp., and Pseudomonas spp. using the agar dilution method and/or the absorbance based microplate assay. MICs were significantly lower in lettuce and beef media than in TSB. Listeria strains were more sensitive than spoilage bacteria, and oregano and thyme were the most active EO's. EO combinations were investigated using the checkerboard method and Oregano combined with thyme had additive effects against spoilage organisms. Combining lemon balm with thyme yielded additive activity against Listeria strains. The effect of simple sugars and pH on antimicrobial efficacy of oregano and thyme was assessed in a beef extract and tomato serum model media. EO's retained greater efficacy at pH5 and 2.32% sugar, but sugar concentrations above 5% did not negatively impact EO efficacy. In addition to proven antimicrobial efficacy, careful selection and investigation of EO's appropriate to the sensory profile of foods and composition of the food system is required. This work shows that EO's might be more effective against food-borne pathogens and spoilage bacteria when applied to foods containing a high protein level at acidic pH, as well as moderate levels of simple sugars.

Frontiers in Microbiology, 2015

Essential oils (EOs) are liquid preparations, produced from plant materials. Although EOs showed a promising bioactivity in vitro, they could interact in foods with some components (fats, proteins, carbohydrates) and pH, thus many authors have reported that a significant effect of EOs toward spoiling and pathogenic microorganisms could be achieved in vivo by using higher amounts of oils. Different methods can be used to assess the bioactivity of EOs (disk diffusion and agar or broth dilution methods); however, there is not a standardized test and researchers propose and use different protocols (evaluating the Minimal Inhibitory Concentration, studying the survival curves, analysis through the scanning electron microscopy, etc.). Thereafter, the scope of this review is a focus on interactions of EOs with proteins, carbohydrates, oils, NaCl, and pH, as well as a brief description on the different protocols to assess their bioactivity both under in vivo and in vitro conditions.

African Journal of Microbiology Research, 2010

The aim of the present study was to assess the effect of extrinsic factors on the antimicrobial effectiveness of essential oils (EOs) against medically important gram positive and gram negative bacteria. Clove, oregano, bay and cinnamon essential oils were tested against Salmonella typhimurium, Escherichia coli, Bacillus cereus and Listeria innocua. Agar diffusion test was used to estimate the strength of the essential oil. Clove was most effective against all groups of bacteria. The minimum inhibition concentrations (MIC) of the four essential oils ranged from 1.25 to 3.50% (v/v) as determined by turbidimetric technique using Biocreen C, analyzer. In order to test the combined effect of pH, sodium chloride, temperature and EOs on the growth of bacteria, the concentrations of the EOs were set at 0.03125% (v/v) below MICs. A synergistic effect against the test bacteria was achieved at the concentration 1.2% (w/v) NaCl and either oregano or clove oil (P < 0.01), however clove was bactericidal on both classes of bacteria at 37°C, pH 5.5 and in combination with NaCl at 1.8% (w/v) pH (7.3), suggesting that EOs can be combined with NaCl at low concentrations overcome organoleptic effects in food and inhibit growth of pathogenic bacteria.

Molecules, 2012

Essential oils (EOs) have been long recognized for their antibacterial, antifungal, antiviral, insecticidal and antioxidant properties. They are widely used in medicine and the food industry for these purposes. The increased interest in alternative natural substances is driving the research community to find new uses and applications of these substances. EOs and their components show promising activities against many food-borne pathogens and spoilage microorganisms when tested in vitro. In food systems, higher concentrations of EOs are needed to exert similar antibacterial effects as those obtained in in vitro assays. The use of combinations of EOs and their isolated components are thus new approaches to increase the efficacy of EOs in foods, taking advantage of their synergistic and additive effects. The purpose of this review is to provide an overview on the antimicrobial efficacy of these combinations. A survey of the methods used for the determination of the interactions and mechanisms involved in the antimicrobial activities of these combinations are also reported.

Antibiotics

The spread of extended-spectrum β-lactamase-producing Escherichia coli and methicillin-resistant Staphylococcus aureus has caused a reduction in antibiotic effectiveness and an increase in mortality rates. Essential oils (EOs), known for their therapeutic efficacy, can be configured as novel broad-spectrum biocides. Accordingly, the bacteriostatic–bactericidal activity of Citrus Lemon (LEO), Pinus Sylvestris (PEO), Foeniculum Vulgaris (FEO), Ocimum Basilicum (BEO), Melissa Officinalis (MEO), Thymus Vulgaris (TEO), and Zingiber Officinalis Rosc. (GEO), at concentrations ranging from 1.25 to 40% (v/v), were tested in vitro against different E. coli and S. aureus strains using minimal inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs). The chemical compositions of the EOs were analyzed using GC/MS. The major components of all seven tested oils were limonene, α-pinene, anethole, estragole, citral, thymol, and zingiberene, respectively. We found that the bact...