Activity Of Plant Essential Oils Research Articles

The Control of Pseudomonas syringae pv. tomato, Causing Bacterial Spot Disease in Tomato, by Different Plant Essential Oils

Seed-borne Pseudomonas syringae pv. tomato causes bacterial spot disease in tomatoes and causes serious economic losses by affecting yield and quality in tomato cultivation. In this study, the effect of essential oils obtained by distillation from Mentha longifolia, Thymus migricus, Salvia hydrangea and Artemisia absinthium and Achillea arabica plants on the control of P. syringae pv. tomato was investigated. The antibacterial activities of plant essential oils against P. syringae pv. tomato were tested by the in vitro agar disk diffusion method. Additionally, minimum inhibitory concentrations at which plant essential oils inhibit the growth of Pst 76 were determined. It was determined that all oils created an inhibition zone between 4.0-30.0 mm against the disease agent and the highest activity was obtained from application with the oil of the T. migricus plant. It was determined that the oils obtained from T. migricus and M. longifolia plants had higher antimicrobial activity than methylmycin in the control group. In line with the results obtained, disease control with essential oils has been seen as an alternative method that can be included in integrated control programs.

The chemical composition and biological activities of plant essential oils against Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae)

The chemical composition and biological activities of plant essential oils against Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae)

The efficient activity of plant essential oils for inhibiting Botrytis cinerea and Penicillium expansum: Mechanistic insights into antifungal activity

Botrytis cinerea and Penicillium expansum produce deterioration in fruit quality, causing losses to the food industry. Thus, plant essential oils (EOs) have been proposed as a sustainable alternative for minimizing the application of synthetic fungicides due to their broad-spectrum antifungal properties. This study investigated the efficacy of five EOs in suppressing the growth of B. cinerea and P. expansum and their potential antifungal mechanisms. EOs of Mentha × piperita L., Origanum vulgare L., Thymus vulgaris L., Eucalyptus globules Labill., and Lavandula angustifolia Mill., were screened for both fungi. The results showed that the EO of T. vulgaris and O. vulgare were the most efficient in inhibiting the growth of B. cinerea and P. expansum. The concentration increase of all EO tested increased fungi growth inhibition. Exposure of fungi to EOs of T. vulgaris and O. vulgare increased the pH and the release of constituents absorbing 260 nm and soluble proteins, reflecting membrane permeability alterations. Fluorescence microscopic examination revealed that tested EOs produce structural alteration in cell wall component deposition, decreasing the hypha width. Moreover, propidium iodide and Calcein-AM stains evidenced the loss of membrane integrity and reduced cell viability of fungi treated with EOs. Fungi treated with EOs decreased the mitochondria activity and the respiratory process. Therefore, these EOs are effective antifungal agents against B. cinerea and P. expansum, which is attributed to changes in the cell wall structure, the breakdown of the cell membrane, and the alteration of the mitochondrial activity.

Screening of insecticidal activity of plant essential oils and extract-based formulations against four agricultural insect pests and their risk assessment

Frankliniella occidentalis (Pergande), Myzus persicae (Sulzer), Plutella xylostella (L), and Spodoptera exigua (Hübner) are notorious agricultural insect pests worldwide. Due to the rapid development of resistance to the conventional insecticides, the number of available insecticides might be reduced in a near future, and botanical insecticides can be considered as one of the potential candidates to solve this problem. In the present study, test formulations were prepared using plant essential oils and extracts as main active ingredients, and their insecticidal activity and phytotoxicity were examined. Among the combinations tested, two oil-in-water formulations of NRS-13 containing thyme white oil and NRS-24 containing basil and rosemary oils were selected based on their notable insecticidal activity and low phytotoxicity. Chemical analyses on the active essential oils, the quantitative analysis of the major components in the formulations, insecticidal activities under pot and field conditions, their acute toxicity on mammals, and ecotoxicity on fish were also examined. The NRS-13 (BaechooSaferTM) and NRS-24 (JindiOutTM) formulations showed species-specific insecticidal activity against P. xylostella and M. persicae, respectively. In addition, both formulations produced low acute oral and dermal toxicity, skin and eye irritation, and fish toxicities, which suggests those formulations based on essential oils could be considered as insecticides for pest control in small-scale environments in organic farming.

Cuticular property affects the insecticidal synergy of major constituents in thyme oil against houseflies, Musca domestica

Plant essential oils are intricate blends comprising predominantly of monoterpenes and some sesquiterpenes. These oils display diverse bioactivities against targeted organisms, often arising from complex interactions among their constituents, which may demonstrate synergistic or antagonistic effects. Despite their wide use as botanical insecticides, the mechanisms behind these interactions and their effects on bioactivity are poorly understood. This study investigated the synergistic interaction of thymol and p-cymene, two major constituents of Thymus vulgaris essential oil, on the larvae and adults of the housefly, Musca domestica. The results showed that p-cymene synergized the insecticidal activity of thymol in adult houseflies, but not in larvae. GC–MS analyses and bioassays indicated the increased cuticular penetration of thymol by p-cymene was the mechanism of synergy, which was observed only in the adults. Two potential routes were proposed: the expansion of the wetting area, or the disruption of cuticular integrity through dissolving the wax layer. The sequential application and large-volume treatment bioassay results suggested that the former was the more likely mechanism. Also, the hydrophobicity of the cuticle seemed critical for this stage-specific synergy. Wax-devoid adults failed to show synergistic toxicity, whereas artificially wax-coated larvae gained a synergistic effect. Overall, the findings provide insights into the synergistic mechanism of insecticidal activity of plant essential oils and suggest potential applications in developing effective strategies using penetration-enhancing synergists.

Activity of plant essential oils against clinically and environmentally isolatedSalmonella entericaserotypes:in vitroassays and molecular docking

This research aimed to evaluate the antimicrobial activity of essential oils (EOs) against clinically and environmentally isolated Salmonella serotypes. Oregano, thyme, and grapefruit EO compounds were identified, and the antimicrobial activity was evaluated against the S. Saintpaul, Oranienburg, and Infantis serotypes. In addition, molecular docking was performed to explore the possible mechanisms between compounds of EOs with microbial enzymes. Thymol was the main compound identified in oregano (44.0%) and thyme (31%) EOs, while d-limonene was present in a greater proportion in grapefruit EO. Oregano EO had the highest antimicrobial activity, followed by thyme and grapefruit EOs. Oregano and thyme EOs illustrated a greater inhibitory capacity to all serotypes, particularly with the environmental S. Saintpaul. Oregano EO presented values of minimum inhibitory concentration (MIC) and minimum bactericidal concentration of 0.1 μL/mL for all serotypes, while thyme and grapefruit EOs presented MIC values of 0.1 μL/mL for the clinical serotypes S. Infantis and S. Oranienburg, respectively. Molecular docking analysis showed the optimal binding free energies for thymol and carvacrol with glucokinase, ATP-dependent-6-fructokinase, outer membrane porin C, and topoisomerase IV. Our results indicate that these EOs can inhibit clinically and environmentally isolated Salmonella serotypes and can be used as alternatives for developing natural food preservatives.

Prolonged Repellent Activity of Plant Essential Oils against Dengue Vector, Aedes aegypti.

Repellents are effective personal protective means against outdoor biting mosquitoes. Repellent formulations composed of EOs are finding increased popularity among consumers. In this study, after an initial screening of 11 essential oils (EOs) at the concentration of 33 μg/cm2, five of the most repellent EOs, Perovskia atriplicifolia, Citrus reticulata (fruit peels), C. reticulata (leaves), Mentha longifolia, and Dysphania ambrosioides were further investigated for repellent activity against Aedes aegypti mosquitoes in time span bioassays. When tested at the concentrations of 33 μg/cm2, 165 μg/cm2 and 330 μg/cm2, the EO of P. atriplicifolia showed the longest repellent effect up to 75, 90 and 135 min, respectively, which was followed by C. reticulata (peels) for 60, 90 and 120 min, M. longifolia for 45, 60 and 90 min, and C. reticulata (leaves) for 30, 45 and 75 min. Notably, the EO of P. atriplicifolia tested at the dose of 330 μg/cm2 showed complete protection for 60 min which was similar to the commercial mosquito repellent DEET. Gas chromatographic-mass spectrometric analyses of the EOs revealed camphor (19.7%), limonene (92.7%), sabinene (24.9%), carvone (82.6%), and trans-ascaridole (38.8%) as the major constituents of P. atriplicifolia, C. reticulata (peels), C. reticulata (leaves), M. longifolia, and D. ambrosioides, respectively. The results of the present study could help develop plant-based commercial repellents to protect humans from dengue mosquitoes.

Research on the Bioactivity of Plant Essential Oils on Armyworm [Mythimna separata (Walker)] Larvae.

In order to find out the biological activity of plant essential oils on armyworm [Mythimna separata (Walker, 1865)] larvae and provide a theoretical basis for the biological control of armyworms, in this study, the antifeedant activity, repellent activity, fumigation activity, contact activity, and synergistic effect on indoxacarb of nine kinds of plant essential oils on armyworm larvae were determined. The results showed that lavender and citronella essential oils had the greatest impact on the antifeedant activity on armyworm larvae, and the antifeedant rate reached 100.00%. Meanwhile, rosemary essential oil revealed the best repellent activity on armyworm larvae with an average dwell time of 0 s at the content of 0.2%. Moreover, tea tree essential oil and lemon essential oil at the content of 2.0% had the best fumigation and contact activity against armyworm larvae, and the corrected mortality rates at 120 h were 86.67 and 66.67%, respectively. In addition, the combination of citronella essential oil and indoxacarb with the ratio of 5:1 had the best synergistic effect on armyworm larvae at 96 h, and the synergistic ratio was reached 100.00%. These findings will guide the development of new insecticides for controlling armyworm larvae.

Behavioral Response, Fumigation Activity, and Contact Activity of Plant Essential Oils Against Tobacco Beetle (Lasioderma serricorne (F.)) Adults.

Tobacco beetle (Lasioderma serricorne (F.)) is one of the main storage pests that harm tobacco leaves. The current control methods mainly include physical control, chemical control, and biological control, but they all have their own disadvantages. In this study, 22 kinds of plant essential oils in grapefruit, peppermint, juniper, eucalyptus, myrrh, lemon grass, geranium, tea tree, cypress, citronella, patchouli, benzoin, rosemary, cinnamon, clary sage, bergamot, mastic, ginger, rose hydrosol, cedar, thyme, and basil, respectively, are selected to explore their behavioral responses against L. serricorne adults using a glass Y-tube olfactometer. The behavioral responses results show that 17 kinds of essential oils in eucalyptus, basil, grapefruit, cypress, mastic, peppermint, patchouli, juniper, geranium, thyme, benzoin, lemon grass, cinnamon, ginger, rosemary, clary sage, and citronella can avoid L. serricorne adults, while five kinds of essential oils in tea tree, rose hydrosol, myrrh, bergamot, and cedar can attract L. serricorne adults. Especially, essential oils in eucalyptus and grapefruit can avoid L. serricorne adults at 1 μl/L with the repellent rates of 94.67 and 94.56%, respectively. Meanwhile, 17 kinds of essential oils which can avoid L. serricorne adults are selected to determine their fumigation activity against L. serricorne adults using the Erlenmeyer flask test method, and bioassay results show that after 72 h of treatment, five kinds of plant essential oils in rosemary, eucalyptus, basil, citronella, and geranium show excellent fumigation activity against L. serricorne adults with the mortality rates of 100.00, 95.29, 95.29, 94.12, and 91.76%, respectively, and their LD50 of the contact activity against L. serricorne adults determined using the leaf-dipping method are 3.60, 3.49, 8.90, 6.70, and 7.80 μl/L, respectively. Our results show that plant essential oils could be developed as environmentally friendly insect control agents.

Antibacterial activity of plant essential oils obtained from Satureja species against Xanthomonas phaseoli pv. phaseoli and Xanthomonas citri subsp. fuscans

In this study, the antibacterial effects of essential oils obtained from different Satureja species (Satureja cuneifolia Ten., Satureja spicigera (C. Koch) Boiss., Satureja thymbra L., Satureja hortensis L. and Satureja cilicica P.H. Davis) against Xanthomonas phaseoli pv. phaseoli (Smith) Vauterin and Xanthomonas citri subsp. fuscans (Burkholder) Starr & Burkholder, which cause common leaf blight in bean plant, were tested. Essential oils were found to significantly inhibit the growth of bacterial strains of both disease agents in vitro, and the lowest concentrations that prevent bacterial growth were determined for both pathogens. The effects of essential oil applications on seed germination, number of infected cotyledons and disease severity were also evaluated. It was determined that essential oils of S. cuneifolia and S. spicigera has no negative effects on seed germination while essential oils of S. hortensis, S. thymbra and S. cilicica caused a little decrease in seed germination compared to the control. As a result of S. cuneifolia + pathogen and S. spicigera + pathogen applications, no infected cotyledons were detected, and it was determined that the disease development caused by two pathogens was prevented by 100%.

Antibacterial activity of plant essential oils against indigenously characterized methicillin-resistant Staphylococcus aureus (MRSA).

Plant essential oils were evaluated for antimicrobial activity against Methicillin-resistant Staphylococcus aureus (MRSA). The isolates (n=03) were procured from Institute of Microbiology, UVAS Lahore, Pakistan. After biochemical and 16S rRNA gene-based PCR characterization, accession numbers were retrieved from NCBI i.e. MW344063.1, MW344064.1 and MW344065.1. These isolates exhibited molecular positivity by multiplex PCR for mecA, coa and eta toxin genes. Moreover, these isolates exhibited resistance to cefoxitin, ampicillin, amoxicillin, penicillin, amoxicillin clavulanate, ciprofloxacin, erythromycin and gentamicin. The antibiotic resistant isolates were evaluated for antimicrobial activity of plant essential oils. The highest zone of inhibition (mean ZOI±S.D.) was measured for Cinnamomum verum (22.67±1.52 mm) followed by Eucalyptus globulus (18.67±2.51 mm) and Syzygium aromaticum (12.67±2.51 mm). Lowest mean MIC value (0.33±0.11 mg/mL) was recorded for E. globulus . Eucalyptus globulus was processed for fractionation by column chromatography and n-hexane, chloroform, n-hexane + chloroform and ethyl-acetate fractions were evaluated for antibacterial activity. Lowest mean MIC (10.04±5.80 mg/mL) was recorded for E. globulus n-hexane fraction. Cell survival percentage of BHK21 cell line was 51.7% at 54.87mg/mL concentration of E. globulus n-hexane fraction. Through gas chromatography-mass spectrometry (GC-MS) analysis of n-hexane fraction, benzene was found abundant (29.9%) as active compound. It was concluded that E. globulus n-hexane fraction exhibited significantly promising results against MRSA .

Fumigant insecticidal activity of plant essential oils against pest blister beetle Epicauta atomaria (Germar) (Coleoptera: Meloidae)

Fumigant insecticidal activity of plant essential oils against pest blister beetle Epicauta atomaria (Germar) (Coleoptera: Meloidae)

Proteomic analysis suggests that monoterpenes in lemongrass disrupt Ca2+ homeostasis in Haemaphysalis longicornis leading to mitochondrial depolarization and cytotoxicity.

Complex mixtures of bioactive ingredients in plant essential oils present complex chemistries which involve different modes of action. An increasing body of scientific reports has recently focused on the acaricidal activities of plant essential oils attributed to their monoterpene components, but information about their underlying molecular mechanism of action is scarce. Here, after the chemical analysis of lemongrass oil, a proteomic analysis of the ovary, salivary gland, and midgut of Haemaphysalis longicornis exposed to Cymbopogon citratus (lemongrass) essential oil was performed via data-independent acquisition mass spectrometry (DIA-MS) technology to further elucidate the molecular mechanisms involved. Pathway analysis reveals the activation of metabolic pathways mediated by oxidoreductases and transferases. Furthermore, the upregulation of various calcium-associated proteins and the upregulation of cytochrome c1, cytochrome c oxidase polypeptide IV, and programmed cell death protein 6-like isoform X1 suggest a cytotoxic mode of action via the formation of reactive oxygen species (ROS), mitochondrial Ca2+ overload, mitochondrial uncoupling, and depolarization, and ATP depletion leading to either apoptotic or necrotic death. Morphological alterations observed after the RNAi of a major detoxification enzyme (glutathione S-transferase) merit further investigation. Hence, the cytotoxic mode of action exhibited by C. citratus oil could be vital for the development of eco-friendly acaricide.

Physical characteristics, chemical compositions, and insecticidal activity of plant essential oils against chicken lice (Menopon gallinae) and mites (Ornithonyssus bursa)

A preparation of essential oils to control chicken lice (Menopon gallinae) and mites (Ornithonyssus bursa) was developed. Each essential oil was effective against lice and mite in vitro. Citronella oil at the lowest concentration of 0.208 µg/cm2 resulted in a mortality rate of 100% in chicken lice, whereas a higher concentration of cloves, lemongrass, ginger, Makwan oil (0.416 µg/cm2), and Litsea oil (0.832 µg/cm2) was also found to be effective. A 100% rate of mortality for mites was observed using citronella and ginger oil at a concentration of 0.416 µg/cm2. At the same concentration, cloves, lemongrass, Litsea, and Makwan oil exhibited mortality rates in mites of 77.96%, 93.33%, 87.30%, and 93.49%, respectively. The efficacy of citronella oil and ginger oil against lice and mites was further examined in vivo. Citronella and ginger oil affected the rate of decline in lice from day 1 to day 14, whereas the number of mites living in nests declined from day 1 to day 7. The reduction of these parasitic insects may be correlated with the chemical constituents present in each essential oil. The active ingredients likely acted insecticidal agents against both parasitic insects. Moreover, the preparation developed here did not cause any side effects, such as dermatitis and respiratory disorders, during animal trials. Hence, preparations comprised of the essential oils of citronella and ginger can be further developed and used as insecticidal agents to control and/or eliminate chicken lice and mites on commercial farms.

The use of cinnamon oil as antibacterial agent to eliminate some antibiotic-resistant bacteria isolated from water sources

The use of cinnamon oil as antibacterial agent to eliminate some antibiotic-resistant bacteria isolated from water sources

Synergistic antimicrobial activities of plant essential oils against Listeria monocytogenes in organic tomato juice

The objective of this study was to identify combinations of plant essential oils (EOs) that have synergistic antilisterial effects in raw organic tomato juice. Among the EOs approved for addition to organic foods in the Republic of Korea, twenty-four EOs were screened for antilisterial activity using a well diffusion assay. Six EOs (cinnamon bark, lemon, lemongrass, oregano, peppermint, and thyme thymol) showed relatively strong inhibitory activities (diameter of zone of inhibition ≥ 35.0 mm) against Listeria monocytogenes. The minimal inhibitory concentrations (MICs) and minimal lethal concentrations (MLCs) of these EOs against L. monocytogenes in a laboratory medium were determined. Oregano and thyme thymol EOs had the lowest MIC (0.3125 μL/mL), and cinnamon bark, oregano, and thyme thymol EOs had the lowest MLC (0.6250 μL/mL). The synergistic antilisterial activities of combinations of EOs in a laboratory medium were determined using a modified checkerboard assay. Combinations of cinnamon bark and lemongrass EOs, cinnamon bark and thyme thymol EOs, and lemongrass and thyme thymol EOs showed synergistic antilisterial activities (fractional inhibitory concentration index = 0.5). A combination of cinnamon bark and thyme thymol EOs was tested for synergistic antilisterial activity in tomato juice incubated at 10 °C and 25 °C for up to 48 h. The number of L. monocytogenes in juice treated with combined EOs at a total concentration of 0.3125 μL/mL decreased significantly (P ≤ 0.05) compared to numbers in juice treated with 0.3125 μL/mL of either cinnamon bark EO or thyme thymol EO alone. These observations show the potential for using combinations of EOs for controlling L. monocytogenes in juice released from cut or bruised raw organic tomatoes intended for consumption in food service or home settings.

Synergistic mechanism of insecticidal activity in basil and mandarin essential oils against the tobacco cutworm

Owing to the complexity in the chemical composition of plant essential oils, they often display enhanced insecticidal activity when applied as a mixture. Although the insecticidal activity of plant essential oils has been gaining more attention recently, understanding in the mechanism of synergy has not been studied as much. In the present study, insecticidal activity of 28 individual essential oils and their mixtures against the third instar larvae of Spodoptera litura was examined. Among the oils tested, basil oil exhibited the strongest contact toxicity, and mandarin oil displayed the greatest boosting effect when the remaining oils were mixed with basil oil. Estragole and linalool were determined as the major active constituents for the insecticidal activity of basil oil and limonene for mandarin oil from the chemical analyses and compound elimination assay. Based on the LD50 values, the binary mixture of basil and mandarin oils exhibited enhanced toxicity compared to the individual application of the two oils, showing synergy ratios of 1.3 and 1.4 from two statistical models. As for the major active compounds, synergistic interaction was found in tertiary mixture of estragole, linalool, and limonene in the blending ratio of 7:2:7, displaying the same insecticidal activity of the binary mixture of basil and mandarin oils. The synergistic effect was only observed in the tertiary mixture, indicating each compound play crucial roles of the overall contact toxicity. Increased penetration through cuticular layer and amplified neurophysiological response were proposed for the mechanism of synergistic effect.

Inhibitory effect of some spice essential oils on growth of some gram‐negative and gram‐positive bacteria and a yeast

Disk diffusion method to determine antimicrobial activity of plant essential oils was used. While the essential oil extracted from oregano has a high effect on nine of our test microorganisms (75%), one of them had a medium effect and two of them had a weak effect in the test results. While the essential oil obtained from thyme was effective on VRE, MSSA, Escherichia feacalis, and Staphylococcus epidermidis, it was not effective on Salmonella enteritidis, Pseudomonas aeruginosa, and Candida albicans. The most effective essential oils on microorganisms were oregano, thyme, and lavandula oils. The essential oils were more effective to MSSA, VRE, E. feacalis, and S. epidermidis. In our study, we aimed to shed light on the beneficial use of herbal products for human health. The pandemic process has shown the importance of fight against pathogenic microorganisms. We believe that this study will contribute to conservation medicine. Practical applications In recent years, plant products such as exytract, essential, oleoresin oil, etc. have become crucial due to the rapid resistance microorganisms have built to antibiotics. Essential oils have been generally used in cosmetics, medicine, and food industries. Also, the volatile compounds obtained from plants have antimicrobial, antifungal, and insecticidal effects. The antimicrobial activity of essential oil is fundamentally attributed to its main components, but the synergistic or antagonistic effect of a compound in the small percentage of the mixture must be taken into consideration.

Determination of Antimicrobial Activity of Various Plant Essential Oils on Vancomycin Resistant Enterococci (VRE) and Some Pathogenic Microorganisms

In this study, it was aimed to determine the anti-bacterial activities of plant essential oils such as thyme, rosemary, sage, linden, black seed, bay leaf, peppermint, parsley, cinnamon and oleagen on vancomycin resistant enterococci (VRE) and pathogenic microorganisms of clinical importance. In the study, the inhibition zones of the plant extract of 10 plants prepared at 2.5 and 5 mg / mlconcentrations of VRE and various pathogenic microorganisms were detected by Disk Diffusion and Agar Well Diffusion Method. Following this, Minimal Inhibition Concentration (MIC) values of these extracts were determined. The activities of plant extracts on DNA and Gas Chromatography-Mass Spectrometry (GC-MS) analyzes were also performed. According to the data obtained, it was determined that the extracts of rosemary and sage plants showed high antibacterial effect against pathogenic bacteria. The rosemary extract was found to be the most effective extract on VRE strains, as well as medium-grade antibacterial effects on the VRE strains in oleaster, linden, thyme and mint extracts. It was also determined that extracts from different plants did not cause any change in the structure of DNA. In our study, it was determined that plant extracts that are especially effective on VRE strains have the potential to be used in the treatment of VRE. The results of this study should be taken into account in the research of drugs that can be used in the treatment of VRE and more in vitro and in vivo research should be carried out in this field.

Antimicrobial Effects of Plant Compounds against Virulent <i>Escherichia coli</i> O157:H7 Strains Containing Shiga Toxin Genes in Laboratory Media and on Romaine Lettuce and Spinach

Escherichia coli strains produce Shiga-toxins Stx-1 and Stx-2 that contribute to their virulence. The objective was to evaluate antimicrobial activities of plant essential oils (oregano, cinnamon, lemongrass), their active components (carvacrol, cinnamaldehyde, citral) and plant-extracts (green tea polyphenols, apple skin, black tea, decaffeinated black tea, grapeseed and pomace extracts) against E. coli O157:H7 strains containing Stx-1 and Stx-2 genes, as determined by Multiplex Polymerase Chain Reaction, in vitro and on leafy greens. Antimicrobials at various concentrations in sterile PBS were added to bacterial cultures (~3 - 4 logs CFU/ml), mixed thoroughly, and incubated at 37°C. Surviving bacteria were enumerated at 0, 1, 3, 5 and 24 h. The most effective essential oil (oregano oil; 0.5%) and plant extract (green tea; 3%) were evaluated against E. coli O157:H7 on romaine lettuce and spinach stored at 4°C for 7 days. Microbial survival was a function of the concentration of antimicrobials and incubation times. All antimicrobials reduced bacterial population to below detection levels in vitro; however, essential oils and active components exhibited greater activity than plant extracts. Oregano oil and green tea reduced E. coli O157:H7 on lettuce and spinach to below detection. Plant-based antimicrobials have the potential to protect foods against E. coli O157: <span style="fo