Screening essential oils for their antimicrobial activities against the foodborne pathogenic bacteria Escherichia coli and Staphylococcus aureus

Litsea cubeba essential oil: Extraction, chemical composition, antioxidant and antimicrobial properties, and applications in the food industry

Litsea cubeba (Lour.) Pers. (Lauraceae) is a valuable industrial crop that produces essential oil. The essential oil extracted from L. cubeba (LCEO) has broad-spectrum antimicrobial activity and high antioxidant properties, with great potential for increased usage in the food industry. This literature review summarizes the extraction techniques, content and chemical composition, and antioxidant and antimicrobial activities of LCEO, with a focus on its usage in the food industry, which is an area of substantial recent research. The chemical composition of LCEO, which is affected by various factors, plays a key role in determining its bioactivity and usage in food. The potent antimicrobial activity of LCEO against various foodborne pathogens gives it potential for use in food packaging and preservation to extend shelf life. Future research challenges include the elucidation of the role and mechanism of individual chemical components of LCEO in inhibiting specific foodborne microorganisms; cultivar development to produce germplasm that yields essential oils of the desired chemical composition; and the development of commercial products that can be used in the food industry.

Antibacterial and Antibiofilm Activity of Croton urticifolius Lam. Essential Oil Via Membrane Disruption

Antimicrobial resistance is a global health issue, in which microorganisms develop resistance to antimicrobial drugs, making infections more difficult to treat. This threatens the effectiveness of standard medical treatments and necessitates the urgent development of new strategies to combat resistant microbes. Studies have increasingly explored natural sources of new antimicrobial agents that harness the rich diversity of compounds found in plant species. This pursuit holds promise for the discovery of novel treatments for combating antimicrobial resistance. In this context, the chemical composition, antibacterial, and antibiofilm activities of the essential oil from Croton urticifolius Lam. leaves (CuEO) were evaluated. CuEO was extracted via hydrodistillation, and its chemical constituents were identified via gas chromatography-mass spectrometry (GC/MS). The antibacterial activity of CuEO was evaluated in a 96-well plate via the microdilution method, and the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values were determined. The effect of CuEO on biofilm formation was assessed by quantifying the biomass using crystal violet staining and viable cell counting. In addition, alterations in the cellular morphology of biofilms treated with CuEO were examined using scanning electron microscopy (SEM) and laser confocal microscopy. GC/MS analysis identified 26 compounds, with elemicine (39.72%); eucalyptol (19.03%), E-caryophyllene (5.36%), and methyleugenol (4.12%) as the major compounds. In terms of antibacterial activity, CuEO showed bacteriostatic effects against Staphylococcus aureus ATCC 700698, S. aureus ATCC 25923, Staphylococcus epidermidis ATCC 12228, and Escherichia coli ATCC 11303, and bactericidal activity against S. aureus ATCC 700698. In addition, CuEO significantly inhibited bacterial biofilm formation. Microscopic analysis showed that CuEO damaged the bacterial membrane by leaching out the cytoplasmic content. Therefore, the results of this study show that the essential oil of C. urticifolius may be a promising natural alternative for preventing infections caused by bacterial biofilms. This study is the first to report the antibiofilm activity of C. urticifolius essential oil.

Potential applications of Rhodomyrtus tomentosa leaf extract as natural anti-staphylococcal additive in food systems: Efficacy and in vivo safety evaluation

This work aimed to explore the potential use of Rhodomyrtus tomentosa ethanol leaf extract (RTEL) as an alternative food preservative agent for controlling the growth of Staphylococcus aureus. Antibacterial activities against food-isolated S. aureus were performed using disc diffusion and broth microdilution assays, followed by evaluating in vivo subacute oral toxicity of the extract. Salad dressing was used as a food model to study bactericidal properties and consumer acceptability. RTEL remarkably inhibited S. aureus with minimum inhibitory concentrations (MICs) ranging from 7.81-62.5 µg/mL. Repeated oral doses (5, 50, and 300 mg/kg RTEL) for 28 days did not affect any of the measured toxicity parameters. The no-observed-adverse-effect-level (NOAEL) of RTEL was noted as more than 300 mg/kg body weight/day. The utilization of RTEL (12.5 mg/mL) in the vinaigrette salad dressing did not affect the consumer acceptability of the product, remarkably killed the pathogen within 3-9 h of exposure. The results indicated that RTEL is safe and effective as a natural anti-staphylococcal controlling agent that could be utilized in food systems. Further work is required on the effects of enterotoxin production, an important virulence factor of S. aureus responsible for food-borne disease.

Analysis of Bioactive Aroma Compounds in Essential Oils from Algerian Plants: Implications for Potential Antioxidant Applications

In samples of Artemisia campestris (AC), Artemisia herba-alba (AHA) and Salvia jordanii (SJ) essential oils, up to 200 distinct volatile compounds were identified. Using headspace solid-phase microextraction combined with gas chromatography-olfactometry-mass spectrometry (HS-SPME-GC-O-MS), different panelists detected 52 of these compounds. This study offers the most detailed analysis of bioactive compound profiles conducted so far. The most abundant compounds identified were curcumene, making up 12.96% of AC, and camphor, constituting 21.67% of AHA and 19.15% of SJ. The compounds with the highest odor activity value (OAV) were (E,Z)-2,4-nonadienal (geranium, pungent), 3-nonenal (cucumber) and 2-undecenal (sweet) in AC, AHA and SJ, respectively. AHA essential oil showed significant antioxidant activity (IC50 = 41.73 ± 4.14 mg/g) and hydroxyl radical generation (hydroxylation percentage = 29.62 ± 3.14), as assessed by the diphenylpicrylhydrazyl (DPPH) method. In terms of oxygen radical absorbance capacity (ORAC), the strongest antioxidant activity was obtained for SJ essential oil (antioxidant activity of the essential oils, AOX = 337.49 ± 9.87).

Use of Essential Oils to Counteract the Phenomena of Antimicrobial Resistance in Livestock Species

Antimicrobial resistance is an increasingly widespread phenomenon that is of particular concern because of the possible consequences in the years to come. The dynamics leading to the resistance of microbial strains are diverse, but certainly include the incorrect use of veterinary drugs both in terms of dosage and timing of administration. Moreover, the drug is often administered in the absence of a diagnosis. Many active ingredients in pharmaceutical formulations are, therefore, losing their efficacy. In this situation, it is imperative to seek alternative treatment solutions. Essential oils are mixtures of compounds with different pharmacological properties. They have been shown to possess the antibacterial, anti-parasitic, antiviral, and regulatory properties of numerous metabolic processes. The abundance of molecules they contain makes it difficult for treated microbial species to develop pharmacological resistance. Given their natural origin, they are environmentally friendly and show little or no toxicity to higher animals. There are several published studies on the use of essential oils as antimicrobials, but the present literature has not been adequately summarized in a manuscript. This review aims to shed light on the results achieved by the scientific community regarding the use of essential oils to treat the main agents of bacterial infection of veterinary interest in livestock. The Google Scholar, PubMed, SciELO, and SCOPUS databases were used for the search and selection of studies. The manuscript aims to lay the foundations for a new strategy of veterinary drug use that is more environmentally friendly and less prone to the emergence of drug resistance phenomena.

Antimicrobial Wound Dressings based on Bacterial Cellulose and Independently Loaded with Nutmeg and Fir Needle Essential Oils

The aim of the present study was to obtain antimicrobial dressings from bacterial cellulose loaded with nutmeg and of fir needle essential oils. The attractive properties of BC, such as biocompatibility, good physicochemical and mechanical stability, and high water absorption, led to the choice of this material to be used as a support. Essential oils have been added to provide antimicrobial properties to these dressings. The results confirmed the presence of oils in the structure of the bacterial cellulose membrane and the ability of the materials to inhibit the adhesion of Staphylococcus aureus and Escherichia coli. By performing antibacterial tests on membranes loaded with fir needle essential oil, we demonstrated the ability of these membranes to inhibit bacterial adhesion to the substrate. The samples loaded with nutmeg essential oil exhibited the ability to inhibit the adhesion of bacteria to the surface of the materials, with the 5% sample showing a significant decrease. The binding of essential oils to the membrane was confirmed by thermal analysis and infrared characterization.

Antibacterial and Antibiofilm Effects of Different Samples of Five Commercially Available Essential Oils

Essential oils (EOs) have gained economic importance due to their biological activities, and increasing amounts are demanded everywhere. However, substantial differences between the same essential oil samples from different suppliers are reported-concerning their chemical composition and bioactivities-due to numerous companies involved in EOs production and the continuous development of online sales. The present study investigates the antibacterial and antibiofilm activities of two to four samples of five commercially available essential oils (Oregano, Eucalyptus, Rosemary, Clove, and Peppermint oils) produced by autochthonous companies. The manufacturers provided all EOs' chemical compositions determined through GC-MS. The EOs' bioactivities were investigated in vitro against Gram-positive (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa). The antibacterial and antibiofilm effects (ABE% and, respectively, ABfE%) were evaluated spectrophotometrically at 562 and 570 nm using microplate cultivation techniques. The essential oils' calculated parameters were compared with those of three standard broad-spectrum antibiotics: Amoxicillin/Clavulanic acid, Gentamycin, and Streptomycin. The results showed that at the first dilution (D1 = 25 mg/mL), all EOs exhibited antibacterial and antibiofilm activity against all Gram-positive and Gram-negative bacteria tested, and MIC value > 25 mg/mL. Generally, both effects progressively decreased from D1 to D3. Only EOs with a considerable content of highly active metabolites revealed insignificant differences. E. coli showed the lowest susceptibility to all commercially available essential oils-15 EO samples had undetected antibacterial and antibiofilm effects at D2 and D3. Peppermint and Clove oils recorded the most significant differences regarding chemical composition and antibacterial/antibiofilm activities. All registered differences could be due to different places for harvesting the raw plant material, various technological processes through which these essential oils were obtained, the preservation conditions, and complex interactions between constituents.

Adaptive ecological knowledge among the Ndjuka Maroons of French Guiana; a case study of two 'invasive species': Melaleuca quinquenervia and Acacia mangium

BACKGROUND

To understand how local ecological knowledge changes and adapts, here in the case of the recent introduction of plant species, we report the knowledge and perceptions of the Ndjuka (Maroon) of French Guiana concerning two tree species, Acacia mangium and niaouli (Melaleuca quinquenervia), which are categorized as "invasive alien plants" in the savannas of their territory.

METHODS

To this end, semi-structured interviews were conducted between April and July 2022, using a pre-designed questionnaire, plant samples and photographs. The uses, local ecological knowledge, and representations of these species were surveyed among populations of Maroon origin in western French Guiana. All responses to closed questions collected during the field survey were compiled into an Excel spreadsheet in order to perform quantitative analyses, including the calculation of use reports (URs).

RESULTS

It appears that the local populations have integrated these two plant species, which are named, used and even traded, into their knowledge systems. On the other hand, neither foreignness nor invasiveness seem to be relevant concepts in the perspective of the informants. The usefulness of these plants is the determining factor of their integration into the Ndjuka medicinal flora, thus resulting in the adaptation of their local ecological knowledge.

CONCLUSION

In addition to highlighting the need for the integration of the discourse of local stakeholders into the management of "invasive alien species," this study also allows us to observe the forms of adaptation that are set in motion by the arrival of a new species, particularly within populations that are themselves the result of recent migrations. Our results furthermore indicate that such adaptations of local ecological knowledge can occur very quickly.

Inactivation of Salmonella using ultrasound in combination with Litsea cubeba essential oil nanoemulsion and its bactericidal application on cherry tomatoes

The presence of Salmonella in nature poses a significant and unacceptable threat to the human public health domain. In this study, the antibacterial effect and mechanism of ultrasound (US) combined with Litsea cubeba essential oil nanoemulsion (LEON) on Salmonella. LEON + US treatment has a significant bactericidal effect on Salmonella. Reactive oxygen species (ROS), malondialdehyde (MDA) detection, N-phenyl-l-naphthylamine (NPN) uptake and nucleic acid release assays showed that LEON + US exacerbated cell membrane lipid peroxidation and increased the permeability of the cell membrane. The results of field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) showed that LEON + US treatment was able to alter cell morphology. It can be observed by flow cytometry (FCM) that LEON + US treatment can cause cell apoptosis. In addition, bacterial counts of cherry tomatoes treated with LEON (0.08 μL/mL) + US (345 W/cm²) for 9 min were reduced by 6.50 ± 0.20 log CFU/mL. This study demonstrates that LEON + US treatment can be an effective way to improve the safety of fruits and vegetables in the food industry.

Effect of Essential Oils of Apiaceae, Lamiaceae, Lauraceae, Myrtaceae, and Rutaceae Family Plants on Growth, Biofilm Formation, and Quorum Sensing in Chromobacterium violaceum, Pseudomonas aeruginosa, and Enterococcus faecalis

The biological role played by essential oils extracted from aromatic plants is progressively being recognized. This study evaluated the potential antibacterial activity of ten essential oils against Chromobacterium violaceum, Pseudomonas aeruginosa, and Enterococcus faecalis by measuring their minimum inhibitory concentration. We found that essential oils exert different antimicrobial effects, with Origanum vulgare and Foeniculum vulgare demonstrating the most significant inhibitory effect on bacterial growth for C. violaceum and E. faecalis. The growth of P. aeruginosa was not affected by any essential oil concentration we used. Sub-inhibitory concentrations of essential oils reduced in C. violaceum and E. faecalis biofilm formation, violacein amount, and gelatinase activity, all of which are biomarkers of the Quorum Sensing process. These concentrations significantly affect the global methylation profiles of cytosines and adenines, thus leading to the hypothesis that the oils also exert their effects through epigenetic changes. Considering the results obtained, it is possible that essential oils can find a broad spectrum of applications in counteracting microbial contamination and preserving sterility of surfaces and foods, as well as inhibiting microbial growth of pathogens, alone or in combination with traditional antibiotics.

Meta-Analysis of In Vitro Antimicrobial Capacity of Extracts and Essential Oils of Syzygium aromaticum, Citrus L. and Origanum L.: Contrasting the Results of Different Antimicrobial Susceptibility Methods

Diffusion methods, including agar disk-diffusion and agar well-diffusion, as well as dilution methods such as broth and agar dilution, are frequently employed to evaluate the antimicrobial capacity of extracts and essential oils (EOs) derived from Origanum L., Syzygium aromaticum, and Citrus L. The results are reported as inhibition diameters (IDs) and minimum inhibitory concentrations (MICs), respectively. In order to investigate potential sources of variability in antimicrobial susceptibility testing results and to assess whether a correlation exists between ID and MIC measurements, meta-analytical regression models were built using in vitro data obtained through a systematic literature search. The pooled ID models revealed varied bacterial susceptibilities to the extracts and in some cases, the plant species and methodology utilised impacted the measurements obtained (p < 0.05). Lemon and orange extracts were found to be most effective against E. coli (24.4 ± 1.21 and 16.5 ± 0.84 mm, respectively), while oregano extracts exhibited the highest level of effectiveness against B. cereus (22.3 ± 1.73 mm). Clove extracts were observed to be most effective against B. cereus and demonstrated the general trend that the well-diffusion method tends to produce higher ID (20.5 ± 1.36 mm) than the disk-diffusion method (16.3 ± 1.40 mm). Although the plant species had an impact on MIC, there is no evidence to suggest that the methodology employed had an effect on MIC (p > 0.05). The ID–MIC model revealed an inverse correlation (R2 = 47.7%) and highlighted the fact that the extract dose highly modulated the relationship (p < 0.0001). The findings of this study encourage the use of extracts and EOs derived from Origanum, Syzygium aromaticum, and Citrus to prevent bacterial growth. Additionally, this study underscores several variables that can impact ID and MIC measurements and expose the correlation between the two types of results.

Antibacterial and Antibiofilm Efficacy of Thyme (Thymus vulgaris L.) Essential Oil against Foodborne Illness Pathogens, Salmonella enterica subsp. enterica Serovar Typhimurium and Bacillus cereus

Nowadays, the wide spread of foodborne illness and the growing concerns about the use of synthetic food additives have shifted the focus of researchers towards essential oils (EOs) as possible antimicrobials and preservatives of natural origin. Thanks to their antimicrobial properties against pathogenic and food spoilage microorganisms, EOs have shown good potential for use as alternative food additives, also to counteract biofilm-forming bacterial strains, the spread of which is considered to be among the main causes of the increase in foodborne illness outbreaks. In this context, the aim of this study has been to define the antibacterial and antibiofilm profile of thyme (Thymus vulgaris L.) essential oil (TEO) against widespread foodborne pathogens, Salmonella enterica subsp. enterica serovar Typhimurium and Bacillus cereus. TEO chemical composition was analyzed through gas chromatography-mass spectrometry (GC-MS). Preliminary in vitro antibacterial tests allowed to qualitatively verify TEO efficacy against the tested foodborne pathogens. The subsequent determination of minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) values allowed to quantitatively define the bacteriostatic and bactericidal effects of TEO. To evaluate the ability of essential oils to inhibit biofilm formation, a microplate assay was performed for the bacterial biofilm biomass measurement. Results suggest that TEO, rich in bioactive compounds, is able to inhibit the growth of tested foodborne bacteria. In addition, the highlighted in vitro anti-biofilm properties of TEO suggest the use of this natural agent as a promising food preservative to counteract biofilm-related infections in the food industry.

Antibacterial Properties of Eucalyptus globulus Essential Oil against MRSA: A Systematic Review

Antimicrobial resistance is a huge threat against the public health sphere and is a major cause of global mortality and morbidity. Antibiotic misuse and overuse have led to the development of many resistant bacterial strains. One particular bacterium of concern is methicillin-resistant Staphylococcus aureus (MRSA), which is the most common resistant bacteria in humans. Antibiotic development has been unable to keep up with the rapid evolution of antibiotic-resistant organisms, and there is an urgent need to identify alternative agents to combat this problem. The purpose of this systematic review is to explore the literature on the antibacterial properties of Eucalyptus globulus essential oil against MRSA. The articles used in this review were obtained through a systematic search of the literature across four databases, with the timeline being between 2002 and 2022. Twenty studies were included in this review, which used various methods to investigate the antibacterial properties of E. globulus essential oil, alone or in combination with other agents, against MRSA. The findings suggest that E. globulus essential oil has antibacterial properties against MRSA, which can be enhanced when used in combination with other agents, such as other essential oils and antibiotics.

Chemical Composition, Antioxidant and Antibacterial Activities of Essential Oil Obtained from Chincho (Tagetes elliptica Sm) Leaves Grown in the Peruvian Andes

The chemical composition, antioxidant, and antibacterial properties of the essential oil from the leaves of Tagetes elliptica Sm., grown in Peru, were studied. The EO was extracted using steam distillation, and its chemical composition was analyzed using GC-MS, while the antioxidant activity was evaluated using the radical, scavenging capacity (DPPH and ABTS assays), and ferric reducing antioxidant power (FRAP) assays, ferrous ion chelating (FIC) activity, and the Rancimat test. The antibacterial activity against Staphylococcus aureus, Escherichia coli, and Salmonella infantis was studied using the agar well diffusion method. Twenty-seven compounds were identified in the essential oil, and the major components were cis-tagetenone (37.27%), trans-tagetenone (18.84%), dihydrotagetone (14.38%), and trans-tagetone (5.15%). With regard to antioxidant properties, the IC₅₀ values obtained for the DPPH, ABTS, and FIC assays were 53.37, 46.38, and 22.65 mg/mL, respectively. These values were lower than those obtained for standard butylated hydroxytoluene and ascorbic acid. In the Rancimat test, antioxidant activity was achieved only at high concentration. T. elliptica essential oil showed a marked antibacterial activity against all bacterial strains at all concentrations assayed. This study demonstrated that T. elliptica essential oil could be considered as an alternative to synthetic antioxidants and antimicrobial agents in the food industry.

Assessment of Genetic Diversity, Micromorphology and Antimicrobial Activity in Nepeta cataria L

The mosquito repellent Nepetalactone rich Nepeta cataria L. (catmint) plant has a variety of therapeutic and industrial potential. Reports on the genetic diversity of N. cataria germplasm are minimal globally and need attention for adding a new variety into commercial cultivation. The present study, therefore, assessed the genetic diversity among thirteen half-sib genotypes of N. cataria using agro economic and phytochemical traits. The experimental set has shown substantial variation for agro economic traits studied. Among all the studied populations, fresh herb-based essential oil content ranged from 0.1 % to 0.3 %, with a grand mean of 1.67 %. However, the estimated oil yield ranged from 44.4 kg/h to 120.73 kg/h with an average of 71.34 kg/h. Among the eleven phytochemical constituents detected in different concentrations in the essential oil of experimental sets, 4aα,7α,7aα-Nepetalactone (67.9-87.5 %) constituted the significant proportion of essential oil. Altogether, based on mean comparison, the population NC8 was found to be promising for estimated oil yield and 4aα,7α,7aα-Nepetalactone content. The greater heritability estimates (h² bs) and genetic advance as percent of mean (GAM) were observed for important economic parameters, i. e., oil content, herb yield, and oil yield. The cluster analysis revealed the least interactions between various agro economic and phytochemical variables. The microscopic study of trichome showed a positive correlation of abaxial leaf surface with essential oil content. The promising antimicrobial potential of catmint oil was also observed against human health-related pathogens. The results infer from our study provide valuable insight for genetic improvement and product development in the catmint germplasm.

Effect of Eugenol, Vanillin, and β-Resorcylic Acid on Foodborne Pathogen Survival in Marinated Camel Meat

The combined inhibitory effect of essential oils (EOs) with meat-based marinades has not been fully studied. Therefore, the present study aimed to gauge the effect of a yogurt-based marinade when individually combined with three EOs, namely eugenol (EU), vanillin (VA), or β-resorcylic acid (BR) on camel meat cubes inoculated with Listeria monocytogenes, Salmonella spp., and Escherichia coli O157:H7 during storage. Fresh camel meat cubes of 10 g were inoculated with bacteria and dipped in the mixture of marinade and EO. Overall, the study had six EO treatments (EU 0.5%, EU 1%, VA 0.5%, VA 1%, BR 0.5%, and BR 1%) and two controls (meat without marinade and marinated meat). Treated meat cubes were stored at 4°C or 10°C for 1, 4, and 7 d. Adding only marinade to the camel meat at 10°C decreased the pathogens by 0.8-2.4 log CFU/g. At 10°C, BR decreased L. monocytogenes, E. coli O157:H7, and Salmonella spp. by 2.0, 1.5, and 1.3 log CFU/g, while EU caused a decrease (p < 0.05) of 1.9, 1.2, and 0.9 log CFU/g, respectively. Similarly, VA caused a reduction in these microorganisms of 1.3, 1.1, and 1.0 log CFU/g, respectively (p < 0.05). The combination of marinade and EO resulted in a decrease of the pathogens ranging from 0.9-1.4 and 2.8-3.7 log CFU/g at 4 and 10°C, respectively. The antimicrobial efficacy of EO alone or when combined with marinade was higher at 10°C than at 4°C with all three pathogens at both 0.5% and 1%. Overall, EOs were found to enhance the microbial safety of camel meat. In addition, they are antimicrobials that occur naturally, require a minimum investment, and may prove to be a great asset for marinated camel meat producers.

Clove Essential Oil and Its Main Constituent, Eugenol, as Potential Natural Antifungals against Candida spp. Alone or in Combination with Other Antimycotics Due to Synergistic Interactions

The occurrence of candidiasis, including superficial infections, has recently increased dramatically, especially in immunocompromised patients. Their treatment is often ineffective due to the resistance of yeasts to antimycotics. Therefore, there is a need to search for new antifungals. The aim of this study was to determine the antifungal effect of clove essential oil (CEO) and eugenol (EUG) towards both reference and clinical Candida spp. strains isolated from the oral cavity of patients with hematological malignancies, and to investigate their mode of action and the interactions in combination with the selected antimycotics. These studies were performed using the broth microdilution method, tests with sorbitol and ergosterol, and a checkerboard technique, respectively. The CEO and EUG showed activity against all Candida strains with a minimal inhibitory concentration (MIC) in the range of 0.25-2 mg/mL. It was also found that both natural products bind to ergosterol in the yeast cell membrane. Moreover, the interactions between CEO and EUG with several antimycotics-cetylpyridinium chloride, chlorhexidine, silver nitrate and triclosan-showed synergistic or additive effects in combination, except nystatin. This study confirms that the studied compounds appear to be a very promising group of phytopharmaceuticals used topically in the treatment of superficial candidiasis. However, this requires further studies in vivo.

Agar Plate Methods for Assessing the Antibacterial Activity of Thyme and Oregano Essential Oils against S. epidermidis and E. coli

The resistance to antimicrobials (AMR), especially antibiotics, represents a serious problem and, at the same time, a challenge. In the last decade, a growing interest in the use of essential oils (EOs) as antimicrobial substances was observed. Commercial thyme and oregano EOs are reported to be the main responsible of the oil antimicrobial efficacy against both Gram-positive and Gram-negative pathogenic bacteria. The aim of the present work was to study the efficacy of EOs against Staphylococcus epidermidis and Escherichia coli in long-time treatments. In a preliminary microdilution test, a MIC value was obtained for thyme EO against S. epidermidis and E. coli. After that, disk diffusion and disk volatilization tests were set up to study the influence of main cultural parameters on EO activity in liquid or vapor phase. Both bacteria were inhibited by thyme and oregano EOs when applied pure (100% v/v) or diluted (75% and 50% v/v): a higher inhibition was observed in a disk diffusion test in which the antimicrobial effect was due to both liquid and vapor phase components. Finally, a comparison with literature data was carried out even if it was not so easy because standard methods are usually modified and adapted to specific case study. For this reason, the results have to be interpreted in relation to the analytical method applied.

Physico-Chemical and Antimicrobial Efficacy of Encapsulated Dhavana Oil: Evaluation of Release and Stability Profile from Base Matrices

Essential oils (EOs) are naturally occurring volatile aromatic compounds extracted from different parts of plants. They are made up of components like terpenes, phenols, etc., and are chemically unstable and susceptible to oxidative deterioration, leading to reduced shelf-life and overall degradation of the product. Encapsulation of EOs in a matrix can prevent degradation of the active ingredient and improve the shelf-life. In this paper, we report encapsulation of Dhavana oil (Artemisia pellen) in a modified starch matrix using a spray-drying technique. Physico-chemical properties of neat and encapsulated Dhavana oil were studied. We selected two powder bases: CaCO₃ and TALC and, loaded neat and encapsulated Dhavana oil in it, studied their stability and interaction with the base matrices at 3 °C, 22 °C and 45 °C up to 2 months under closed conditions and one week at 22 °C and 45 °C under open condition. Thermal degradation pattern was studied for neat and encapsulated Dhavana oil and modified starch. Release of primary active component of neat and encapsulated Dhavana oil from the base matrices was evaluated with GCMS. Stability study and release mechanism were elucidated to understand the release pattern in different base powders under similar conditions. Retention of hydroxydhavanone was found to be better in TALC than CaCO₃, and therefore, the former can be considered a suitable base matrix for developing a stable powder formulation with an optimum release of the oil. Dhavana oil is known for its anti-microbial activity, and hence, neat and encapsulated Dhavana oil was tested on different bacterial and fungal strains. The encapsulated oil depicted good anti-microbial efficacy against various bacterial and fungal strains, which is a step forward for developing anti-microbial formulations. Thus, the reported work will provide helpful information on cosmetic formulation and, therefore, be useful for perfumery, food, and cosmetic industries.

Determining the Antibiofilm Efficacy of Oregano Gel in an Ex Vivo Model of Percutaneous Osseointegrated Implants

Biofilm contamination is common in patients with percutaneous osseointegrated (OI) implants, leading to frequent infections, irritation, and discomfort. Reported infection rates soar up to 65% as the recalcitrant nature of biofilms complicates treatment. There is persistent need for therapies to manage biofilm burden. In response, we formulated and tested oregano essential oil in a topical gel as a potential biofilm management therapy. We developed an ex vivo system based on an established ovine OI implant model with Staphylococcus aureus ATCC 6538 biofilms as initial inocula. Gel was administered to the samples across a period of five days. Samples were quantified and colony forming unit (CFU) counts were compared against a positive control (initial bacterial inocula without treatment). Significant biofilm reduction was observed in samples treated with oregano gel compared to controls, demonstrating the potential of an oregano oil-based gel as a biofilm management therapy at the skin-implant interface of percutaneous OI implants.

Utilization of FMOC-3F-PHE hydrogel for encapsulation of Zanthoxylum armatum and Cinnamomum camphora oil for enhancing their antibacterial activity

Objective

While essential oils have many applications in medicine, not many studies have been done in the past to address issues of active targeting, enhancing bioavailability and reducing toxicity at higher concentrations. Herein, we used Fmoc-3F-Phe amino acid hydrogels to address such issues by encapsulating essential oils, Zanthoxylum armatum and Cinnamomum camphora, in its system and allowing sustained-release of these oils onto bacterial assays of E. coli ATCC 25922, P. hauseri NBRC 3851, M. luteus KACC 13377, and B. subtilis ATCC 66333 for probing enhanced antibacterial properties of the oils by prolonging its efficacy through controlled-release mechanism.

Results

We found that while Zanthoxylum oil showed no particular difference in enhancing the antibacterial property against the three fast growing bacteria, however profound variation was observed against slow growing bacteria B. subtilis. The hydrogel encapsulated oil was able to retain its antibacterial property for a longer time while directly applied oil could not for this bacteria. Even for highly volatile camphor oil, the oil itself failed to show any antibacterial property with direct use, however the hydrogel encapsulated oil was able to show excellent antibacterial property for B. subtilis and M. luteus through prohibition of sublimation via encapsulation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13104-022-06163-4.

Chemical Composition, Antioxidant, Antibacterial, and Antibiofilm Activities of Backhousia citriodora Essential Oil

The essential oil of Backhousia citriodora, commonly known as lemon myrtle oil, possesses various beneficial properties due to its richness in bioactive compounds. This study aimed to characterize the chemical profile of the essential oil isolated from leaves of Backhousia citriodora (BCEO) and its biological properties, including antioxidant, antibacterial, and antibiofilm activities. Using gas chromatography–mass spectrometry, 21 compounds were identified in BCEO, representing 98.50% of the total oil content. The isomers of citral, geranial (52.13%), and neral (37.65%) were detected as the main constituents. The evaluation of DPPH radical scavenging activity and ferric reducing antioxidant power showed that BCEO exhibited strong antioxidant activity at IC₅₀ of 42.57 μg/mL and EC₅₀ of 20.03 μg/mL, respectively. The antibacterial activity results showed that BCEO exhibited stronger antibacterial activity against Gram-positive bacteria (Staphylococcus aureus and Staphylococcus epidermidis) than against Gram-negative bacteria (Escherichia coli and Klebsiella pneumoniae). For the agar disk diffusion method, S. epidermidis was the most sensitive to BCEO with an inhibition zone diameter of 50.17 mm, followed by S. aureus (31.13 mm), E. coli (20.33 mm), and K. pneumoniae (12.67 mm). The results from the microdilution method showed that BCEO exhibited the highest activity against S. epidermidis and S. aureus, with the minimal inhibitory concentration (MIC) value of 6.25 μL/mL. BCEO acts as a potent antibiofilm agent with dual actions, inhibiting (85.10% to 96.44%) and eradicating (70.92% to 90.73%) of the biofilms formed by the four tested bacteria strains, compared with streptomycin (biofilm inhibition, 67.65% to 94.29% and biofilm eradication, 49.97% to 89.73%). This study highlights that BCEO can potentially be a natural antioxidant agent, antibacterial agent, and antibiofilm agent that could be applied in the pharmaceutical and food industries. To the best of the authors’ knowledge, this is the first report, on the antibiofilm activity of BCEO against four common nosocomial pathogens.

Biological properties of Thymus zygis essential oil with emphasis on antimicrobial activity and food application

The Thymus plants have been used for centuries in traditional medicine and as a food spice, among this genus, Thymus zygis (red thyme) is a widespread plant, vastly used as a culinary flavouring agent. Its essential oil has demonstrated diverse bioactive properties, such as antimicrobial, insecticidal, larvicidal and antiparasitic activities. Numerous studies have characterized this essential oil showing that it possesses a broad antimicrobial spectrum and may even enhance the effect of certain antimicrobial agents. Its potential application as a food preservative has been analysed on different matrixes pointing to its antimicrobial activity against spoilage and pathogenic microorganisms in food. This review provides an insight in the chemical composition, antimicrobial, insecticidal, larvicidal and antiparasitic activities and toxicity of T. zygis essential oil, as well as its potential application in food as a preservative.

Antibacterial Activity and Epigenetic Remodeling of Essential Oils from Calabrian Aromatic Plants

Natural compounds have historically had a wide application in nutrition. Recently, a fundamental role has been identified for essential oils extracted from aromatic plants for their nutritional, antimicrobial, and antioxidant properties, and as food preservatives. In the present study, essential oils (EOs) from ten aromatic plants grown in Calabria (Italy), used routinely to impart aroma and taste to food, were evaluated for their antibacterial activity. This activity was investigated against Escherichia coli strain JM109, and its derived antibiotic-resistant cells selected by growing the strain at low concentrations of ampicillin, ciprofloxacin, and gentamicin by measuring the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC). Although all the essential oils showed bactericidal activity, those from Clinopodium nepeta, Origanum vulgare, and Foeniculum vulgare displayed the greatest inhibitory effects on the bacterial growth of all cell lines. It is plausible that the antibacterial activity is mediated by epigenetic modifications since the tested essential oils induce methylation both at adenine and cytosine residues in the genomes of most cell lines. This study contributes to a further characterization of the properties of essential oils by shedding new light on the molecular mechanisms that mediate these properties.

Evaluating the Efficacy of 30 Different Essential Oils against Varroa destructor and Honey Bee Workers (Apis mellifera)

Simple Summary

Worldwide, mass losses of honey bee colonies are being observed more frequently due to Varroa mite infestation. Therefore, varroosis is considered a major problem in beekeeping participating to a large extent in colony collapse disorder. Except for direct damage of bees and suppressing their immune system caused by parasitism, Varroa mites transfer viral particles straight to bee hemolymph which can have a fatal impact. To control the mite population, several acaricidal treatments are used. Commonly used treatments are synthetic acaricides with a high risk of developing Varroa resistance population and contamination of bee products by acaricidal residues. Other commonly used treatments are organic acids, which are increasingly associated with damage of brood, adult bees, and premature deaths of queens. Therefore, in this study, we evaluated the varroacidal effect of 30 individual essential oils. The toxicity of the most effective oils selected by screening was subsequently tested on Varroa mites and adult honey bee workers simultaneously. In addition, the main components of these essential oils were specified. Several essential oils were proven to be effective against the adult female of Varroa mites and at the same dose safe for adult honey bee workers under laboratory conditions, especially manuka, peppermint, oregano, litsea, and cinnamon.

Abstract

Essential oils and their components are generally known for their acaricidal effects and are used as an alternative to control the population of the Varroa destructor instead of synthetic acaricides. However, for many essential oils, the exact acaricidal effect against Varroa mites, as well as the effect against honey bees, is not known. In this study, 30 different essential oils were screened by using a glass-vial residual bioassay. Essential oils showing varroacidal efficacy > 70% were tested by the complete exposure assay. A total of five bees and five mites were placed in the Petri dishes in five replications for each concentration of essential oil. Mite and bee mortality rates were assessed after 4, 24, 48, and 72 h. The LC₅₀ values and selectivity ratio (SR) were calculated. For essential oils with the best selectivity ratio, their main components were detected and quantified by GC-MS/MS. The results suggest that the most suitable oils are peppermint and manuka (SR > 9), followed by oregano, litsea (SR > 5), carrot, and cinnamon (SR > 4). Additionally, these oils showed a trend of the increased value of selective ratio over time. All these oils seem to be better than thymol (SR < 3.2), which is commonly used in beekeeping practice. However, the possible use of these essential oils has yet to be verified in beekeeping practice.

Bioactive Collagen Hydrolysate-Chitosan/Essential Oil Electrospun Nanofibers Designed for Medical Wound Dressings

In this study, lemon balm (Melissa officinalis L.) and dill (Anethum graveolens L.) essential oils (EOs) were encapsulated into collagen hydrolysates extracted from bovine tendons and rabbit skins, both mixed with chitosan (CS) by using the coaxial electrospinning technique for potential wound dressing applications. The morphology and chemical composition of the electrospun nanofibers were investigated using scanning electron microscopy (SEM) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). The antimicrobial activity of the dill EO and lemon EO, as well as the electrospun samples loaded with essential oils was determined by disk diffusion assay against Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, Enterococcus faecalis ATCC 29212, and Salmonella typhimurium ATCC 14028 bacterial strains; Candida albicans ATCC 10231 and Candida glabrata ATCC 90028 yeast strains; and Aspergillus brasiliensis ATCC 9642 fungal strain. In vivo biocompatibility testing of the collagen hydrolysate-chitosan/essential oil electrospun nanofibers was based on the determination of the hematological, biochemical, and immunological profile and the evaluation of the influence produced on the oxidative stress in white Swiss mice. The synergetic effect of dill and lemon balm EOs can improve the antimicrobial activity of collagen hydrolysate-chitosan nanofibers against the most important bacterial strains. The in vivo test results suggested a good biocompatibility of electrospun samples based on collagen hydrolysate extracted from bovine tendons or rabbit skin mixed with chitosan and containing dill and/or lemon balm essential oils as encapsulated bioactive compounds.

Antibacterial kinetics and phylogenetic analysis of Aloe vera plants

Uncontrolled use of antibiotics has resulted in the emergence of resistant bacteria. It has necessitated the evaluation of antibacterial activities and phylo-diversity of Aloe vera (also called Aloe barbadensis) plants as antimicrobial agent in Nigeria. Biotyped enteric bacilli of 251 strains obtained from fecal samples of patients with various gastro-intestinal complications are profiled for antibiogram. Resistant biotypes were assayed for susceptibility to Aloe vera latex and further evaluated for time-kill kinetics and phylo-diversity. More than 30% of enteric bacilli, including Citrobacter freundii, Escherichia coli and Proteus mirabilis were resistant to cotrimoxazole, ciprofloxacin, and tetracycline respectively at MIC >16 µg/ml (p=0.004). Aloe vera latex significantly inhibited 39.5% resistant enteric biotypes with a significant average reduction of the viable count at 1xMIC and 2xMIC to less than 3.0 Log10CFU/mL after 24 hours. Flavonoids, alkaloids, terpenoids and anthraquinine in anti-enteric sap significantly correlated and regressed with antibacterial activity (p<0.05), while two of the antimicrobial Aloe vera plants showed phylogenetic relatedness with other homologous. Anti-bacteria efficacy of some Nigerian Aloe vera latex could provide alternative therapy, while its phylo-diversity and genomic profiling would offer a promising avenue for identification and development of antimicrobial agents as drug candidates for natural antibiotics.

An Evaluation of the Potential of Essential Oils against SARS-CoV-2 from In Silico Studies through the Systematic Review Using a Chemometric Approach

Essential oils (EOs) and their compounds have attracted particular attention for their reported beneficial properties, especially their antiviral potential. However, data regarding their anti-SARS-CoV-2 potential are scarce in the literature. Thus, this study aimed to identify the most promising EO compounds against SARS-CoV-2 based on their physicochemical, pharmacokinetic, and toxicity properties. A systematic literature search retrieved 1669 articles; 40 met the eligibility criteria, and 35 were eligible for analysis. These studies resulted in 465 EO compounds evaluated against 11 human and/or SARS-CoV-2 target proteins. Ninety-four EO compounds and seven reference drugs were clustered by the highest predicted binding affinity. Furthermore, 41 EO compounds showed suitable drug-likeness and bioactivity score indices (≥0.67). Among these EO compounds, 15 were considered the most promising against SARS-CoV-2 with the ADME/T index ranging from 0.86 to 0.81. Some plant species were identified as EO potential sources with anti-SARS-CoV-2 activity, such as Melissa officinalis Arcang, Zataria multiflora Boiss, Eugenia brasiliensis Cambess, Zingiber zerumbet Triboun & K.Larsen, Cedrus libani A.Rich, and Vetiveria zizanoides Nash. Our work can help fill the gap in the literature and guide further in vitro and in vivo studies, intending to optimize the finding of effective EOs against COVID-19.

Clove Buds Essential Oil: The Impact of Grinding on the Chemical Composition and Its Biological Activities Involved in Consumer's Health Security

This study is aimed at identifying the chemical composition of the essential oil extracted from the Syzygium aromaticum seeds, as well as investigating its biological activities, insecticide effect, and allelopathic properties. The extraction yield was about 14.3 and 7.14% for grounded and ungrounded seeds, respectively. The GC-MS analysis allowed the identification of 17 heterogeneous compounds, including eugenol (68.7-87.4%), as major compound, cyperene (20.5-7.2%), phenethyl isovalerate (6.4-3.6%), and cis-thujopsene (1.9-0.8%), respectively, for grounded and ungrounded seeds. Concerning the antibacterial activity, the diameter of the inhibition zone reached 35 mm when the essential oil extracted from grounded seeds was applied against Escherichia coli. Regarding the antioxidant activity via the DPPH radical scavenging test, the IC₅₀ varied from 1.2 ± 0.1 to 2.8 ± 0.5 μg/mL. With respect to reducing power, the efficient concentration EC₅₀ ranged from 32 to 50 μg/mL. The essential oil exhibited also an allelopathic effect against seeds of Hyoscyamus niger, as well as an insecticide effect against Sitophilus oryzae with a DL₅₀ value of 252.4 μL/L air. These findings enhance the use of this spice as a natural food preservative and encourage its use in several fields, including pharmaceutical, cosmetics, agriculture, and therapy, that could be a strategic way to guarantee the consumer's health.

Backhousia citriodora F. Muell. (Lemon Myrtle), an Unrivalled Source of Citral

Lemon oils are amongst the highest volume and most frequently traded of the flavor and fragrance essential oils. Citronellal and citral are considered the key components responsible for the lemon note with citral (neral + geranial) preferred. Of the myriad of sources of citral, the Australian myrtaceous tree, Lemon Myrtle, Backhousia citriodora F. Muell. (Myrtaceae), is considered superior. This review examines the history, the natural occurrence, the cultivation, the taxonomy, the chemistry, the biological activity, the toxicology, the standardisation and the commercialisation of Backhousia citriodora especially in relation to its essential oil.

A Review on Cistus sp.: Phytochemical and Antimicrobial Activities

Resistance to drugs is reaching alarming levels and is placing human health at risk. With the lack of new antimicrobials drugs, infectious diseases are becoming harder to treat. Hence, there is an increasing awareness of active phytochemicals with therapeutic functions. The tremendous research interest on the Cistus L. genus includes numerous plants used in traditional medicine by people living around the Mediterranean Sea, also resulted in some interesting discoveries and written literature. This review aimed at gathering scientific literature about Cistus species, describing phytochemical profiles and the various pharmacological activities. We also extensively reviewed the antimicrobial activities, including antiviral, antiparasitic, antifungal, and antibacterial potentials of Essential Oils (EO), raw extracts as well as isolated compounds. Mechanisms of action along with methods used are also investigated in this review. Considering the findings of the Cistus species extracts, this genus offers an adequate reserve of active phytochemicals since many have been used to create drugs. Therefore, this review work can serve society by providing a global view on Cistus L. sp. regarding pharmacological potentials and their chemical profiles.

Activity of Liquid and Volatile Fractions of Essential Oils against Biofilm Formed by Selected Reference Strains on Polystyrene and Hydroxyapatite Surfaces

Biofilms are surface-attached, structured microbial communities displaying higher tolerance to antimicrobial agents in comparison to planktonic cells. An estimated 80% of all infections are thought to be biofilm-related. The drying pipeline of new antibiotics efficient against biofilm-forming pathogens urges the search for alternative routes of treatment. Essential Oils (EOs), extracted from medicinally important plants, are a reservoir of bioactive compounds that may serve as a foothold in investigating novel antibiofilm compounds. The aim of this study was to compare antimicrobial activity of liquid and volatile fractions of tested EOs against biofilm-forming pathogens using different techniques. In this research, we tested five EOs, extracted from Syzygium aromaticum L., Boswelia serrata Roxb., Juniperus virginiana L., Pelargonium graveolens L. and Melaleuca alternifolia Cheel., against planktonic and biofilm forms of five selected reference strains, namely Staphylococcus aureus, Enterococcus faecalis, Klebsiella pneumoniae, Pseudomonas aeruginosa, Escherichia coli, and Candida albicans. To obtain cohesive results, we applied four various methodological approaches: to assess the activity of the liquid fraction of EOs, disc diffusion and the microdilution method were applied; to test EOs’ volatile fraction, the AntiBioVol assay and modified Antibiofilm Dressing Activity Measurement (A.D.A.M.) were used. The molecular composition and dynamics of antimicrobial substances released from specific EOs was measured using Gas Chromatography–Mass Spectrometry (GC-MS). The antimicrobial potency of EO’s volatile fraction against biofilm formed by tested strains differed from that of the liquid fraction and was related to the molecular weight of volatile compounds. The liquid fraction of CW-EO and volatile fraction of F-EO acted in the strongest manner against biofilm of C. albicans. The addition of 0.5% Tween 20 to liquid phase, enhanced activity of G-EO against E. coli and K. pneumoniae biofilm. EO activity depended on the microbial species it was applied against and the chosen assessment methodology. While all tested EOs have shown a certain level of antimicrobial and antibiofilm effect, our results indicate that the choice of EO to be applied against a specific biofilm-forming pathogen requires careful consideration with regard to the above-listed aspects. Nevertheless, the results presented in this research contribute to the growing body of evidence indicating the beneficial effects of EOs, which may be applied to fight biofilm-forming pathogens.

Nanoemulsion-Based Technologies for Delivering Natural Plant-Based Antimicrobials in Foods

There is increasing interest in the use of natural preservatives (rather than synthetic ones) for maintaining the quality and safety of foods due to their perceived environmental and health benefits. In particular, plant-based antimicrobials are being employed to protect against microbial spoilage, thereby improving food safety, quality, and shelf-life. However, many natural antimicrobials cannot be utilized in their free form due to their chemical instability, poor dispersibility in food matrices, or unacceptable flavor profiles. For these reasons, encapsulation technologies, such as nanoemulsions, are being developed to overcome these hurdles. Indeed, encapsulation of plant-based preservatives can improve their handling and ease of use, as well as enhance their potency. This review highlights the various kinds of plant-based preservatives that are available for use in food applications. It then describes the methods available for forming nanoemulsions and shows how they can be used to encapsulate and deliver plant-based preservatives. Finally, potential applications of nano-emulsified plant-based preservatives for improving food quality and safety are demonstrated in the meat, fish, dairy, and fresh produce areas.

Evaluation of the inhibitory activity of essential oils against spoilage yeasts and their potential application in yogurt

Yeasts are the leading cause of spoilage in yogurt. Considering the high demand from consumers to use natural products as an alternative to additives, essential oils (EOs) could be a promising solution to guarantee high microbiological standards. The present study highlighted the in vitro antifungal potential of cinnamon, ginger, lemongrass, mandarin, orange, lemon and lime EOs against spoilage yeasts isolated from yogurts prepared with pasteurized buffalo milk. A total of 74 isolates represented by 14 different species of Candida, Rhodotorula, Debaryomyces, Kluyveromyces and Yarrowia genera were subjected to a disc diffusion assay, showing lemongrass EO to have the highest antifungal activity (40.97 ± 9.86 mm), followed by cinnamon (38.46 ± 6.59 mm) and orange (12.00 ± 4.52 mm) EOs. Yarrowia lipolytica was less susceptible to lemongrass EO than Candida sake and Yarrowia deformans isolates. Ginger EO exhibited the lowest efficacy. A minimum inhibitory concentration (MIC) assay showed the ability of lemongrass and cinnamon EOs to inhibit the growth of all selected isolates at concentrations between ≤0.31 and 1.25 μL/mL. Therefore, for the first time, the two best-performing EOs (lemongrass and cinnamon) based on in vitro assays were assessed for their potential roles as preservatives in an in vivo yogurt model prepared at the laboratory scale. Since some limitations, such as the inhibition of lactic acid bacteria by cinnamon EO, consequently leading to fermentation failure as well as species-specific antifungal activity of lemongrass EO, were observed, further studies are needed to explore the possibility of using a slightly higher concentration of lemongrass EO and/or combinations of different EOs and/or their components. Finally, since yogurt spoilage could also be prevented by correct sanitation procedures of the production environment, the sanitizers commonly used in the food industry were tested against all isolates, showing the high efficiency of alcohol-based sanitizers and the ineffectiveness of chlorine-based sanitizers.

A Systematic Review of Plants With Antibacterial Activities: A Taxonomic and Phylogenetic Perspective

Background: Antimicrobial resistance represents a serious threat to human health across the globe. The cost of bringing a new antibiotic from discovery to market is high and return on investment is low. Furthermore, the development of new antibiotics has slowed dramatically since the 1950s' golden age of discovery. Plants produce a variety of bioactive secondary metabolites that could be used to fuel the future discovery pipeline. While many studies have focused on specific aspects of plants and plant natural products with antibacterial properties, a comprehensive review of the antibacterial potential of plants has never before been attempted. Objectives: This systematic review aims to evaluate reports on plants with significant antibacterial activities. Methods: Following the PRISMA model, we searched three electronic databases: Web of Science, PubMed and SciFinder by using specific keywords: "plant," "antibacterial," "inhibitory concentration." Results: We identified a total of 6,083 articles published between 1946 and 2019 and then reviewed 66% of these (4,024) focusing on articles published between 2012 and 2019. A rigorous selection process was implemented using clear inclusion and exclusion criteria, yielding data on 958 plant species derived from 483 scientific articles. Antibacterial activity is found in 51 of 79 vascular plant orders throughout the phylogenetic tree. Most are reported within eudicots, with the bulk of species being asterids. Antibacterial activity is not prominent in monocotyledons. Phylogenetic distribution strongly supports the concept of chemical evolution across plant clades, especially in more derived eudicot families. The Lamiaceae, Fabaceae and Asteraceae were the most represented plant families, while Cinnamomum verum, Rosmarinus vulgaris and Thymus vulgaris were the most studied species. South Africa was the most represented site of plant collection. Crude extraction in methanol was the most represented type of extraction and leaves were the main plant tissue investigated. Finally, Staphylococcus aureus was the most targeted pathogenic bacteria in these studies. We closely examine 70 prominent medicinal plant species from the 15 families most studied in the literature. Conclusion: This review depicts the current state of knowledge regarding antibacterials from plants and provides powerful recommendations for future research directions.

Vapors of Volatile Plant-Derived Products Significantly Affect the Results of Antimicrobial, Antioxidative and Cytotoxicity Microplate-Based Assays

Volatile plant-derived products were observed to exhibit broad spectrum of biological effects. However, due to their volatility, results of conventional microplate-based bioassays can be significantly affected by the vapors. With aim to demonstrate this phenomenon, antimicrobial, antioxidant, and cytotoxic activities of three essential oils (Alpinia elegans, Cinnamomum iners, and Xanthostemon verdugonianus), one supercritical CO2 extract (Nigella sativa), and four plant-derived compounds (capsaicin, caryophyllene oxide, 8-hydroxyquinoline, and thymoquinone) were evaluated in series of experiments including both ethylene vinyl acetate (EVA) Capmat sealed and nonsealed microplates. The results clearly illustrate that vapor transition to adjoining wells causes false-positive results of bioassays performed in nonsealed microtiter plates. The microplate layout and a duration of the assay were demonstrated as the key aspects defining level of the results affection by the vapors of volatile agents. Additionally, we reported biological activities and chemical composition of essential oils from A. elegans seeds and X. verdugonianus leaves, which were, according to our best knowledge, analyzed for the first time. Considering our findings, certain modifications of conventional microplate-based assays are necessary (e.g., using EVA Capmat as vapor barrier) to obtain reliable results when biological properties of volatile agents are evaluated.

Unraveling the anti-bacterial mechanism of Litsea cubeba essential oil against E. coli O157:H7 and its application in vegetable juices

Recently, natural essential oils have been extensively studied for anti-bacterial application in foods due to their safety and high biological activity. Herein, Litsea cubeba essential oil (LC-EO) was applied as a natural anti-bacterial agent for exploring its anti-bacterial mechanism against Enterohemorrhagic Escherichia coli O157:H7 (EHEC O157:H7). The LC-EO could effectively inhibit the growth of EHEC O157:H7 and the minimal inhibitory concentration (MIC) was 0.5 mg/mL. In the study of anti-bacterial mechanism, the LC-EO was proved with good membrane penetration ability, which could destroy bacterial cell structure and disorder membrane permeability, thereby causing the leakage of intracellular organic matters. Furthermore, the inhibitory effects of LC-EO on physiological metabolism of EHEC O157:H7, including respiratory metabolism, enzyme activity, the replication of nucleic acid and the transcription level of main virulence genes (stx1, stx2, ehxA, eae), were also demonstrated in this study. Specially, the possible action mechanism of different components of LC-EO on bacterial genetic material was revealed deeply on molecular level by the molecular docking technology. Finally, the results of application evaluation indicated that the addition of LC-EO at MIC in different vegetable juices could maintain anti-bacterial rate above 99.9% for 4 days without remarkable influence on foods sensory quality. The information in this study provides the necessary theoretical foundation for extending the application of LC-EO in food preservation.

Optimisation of Sequential Microwave-Assisted Extraction of Essential Oil and Pigment from Lemon Peels Waste

In this work, a cascade approach to obtain different valuable fractions from lemon peels waste was optimised using microwave-assisted processes. Microwave-assisted hydrodistillation (MAHD) with a Clevenger apparatus was firstly used to obtain the lemon essential oil (LEO). The remaining residue was then submitted to microwave-assisted extraction (MAE) to extract the lemon pigment (LP). A Box-Behnken design was used to evaluate the influence of ethanol concentration, temperature and time in LP extraction in terms of extraction yield and colour intensity. Optimal extraction conditions for LP were 80% (v/v) ethanol, 80 °C and 50 min, with a liquid-to-solid ratio of 1:10. The obtained yields for LEO and LP were around 2 wt.% and 6 wt.%, respectively. The composition of LEO was analysed by gas chromatography with flame ionisation detection (GC-FID), and limonene (65.082 wt.%), β-pinene (14.517 wt.%) and γ-terpinene (9.743 wt.%) were mainly identified. LP was purified by using different Amberlite adsorption resins (XAD4, XAD7HP and XAD16N), showing XAD16N the best adsorption capacity. Enrichment factors of 4.3, 4.5 and 5.0 were found for eriocitrin, diosmin and hesperidin, respectively, which were detected as the main components in LP by ultra-high-performance liquid chromatography-diode array detector-tandem mass spectrometry (UPLC-DAD-MS) analysis, with final concentrations of 4.728 wt.%, 7.368 wt.% and 2.658 wt.%, respectively. Successful antimicrobial capacity against Escherichia coli and Staphylococcus aureus was obtained for LEO. The results from this work showed the potential of applying a cascading approach based on microwave-assisted processes to valorise lemon wastes, obtaining natural pigments and antimicrobials to be applied in food, cosmetic and polymer industries.

Essential oils as additives in active food packaging

Food packaging can be considered as a passive barrier that protects food from environmental factors such as ultraviolet light, oxygen, water vapour, pressure and heat. It also prolongs the shelf-life of food by protecting from chemical and microbiological contaminants and enables foods to be transported and stored safely. Active packaging (AP) provides the opportunity for interaction between the external environment and food, resulting in extended shelf-life of food. Chemoactive packaging has an impact on the chemical composition of the food product. The application of natural additive such as essential oils in active packaging can be used in the forms of films and coatings. It has been observed that, AP helps to maintain temperature, moisture level and microbial and quality control of the food. This review article provides an overview of the active packaging incorporated with essential oils, concerns and challenges in industry, and the effect of essential oil on the packaging microstructure, antioxidant and antimicrobial properties.

The effect of essential oils and their combinations on bacteria from the surface of fresh vegetables

During the study, we determined the antimicrobial activity of different selected essential oils (thyme, lemongrass, juniper, oregano, sage, fennel, rosemary, mint, rosehips, dill) on some pathogenic and spoilage bacteria isolated from the surface of various fresh vegetables. At the same time, in the case of some volatile oil combinations we followed the phenomena of synergism and antagonism. The identification of the isolated bacterial strains was made using 16S rDNA gene sequence analysis. The most resistant isolates appeared to be Curtobacterium herbarum, Achromobacter xylosoxidans, and Enterobacter ludwigii, while Pseudomonas hibiscicola was the most sensitive. Of the chosen plant essential oils, the most pronounced antimicrobial effect was detected in the case of oregano. The essential oils of thyme and mint also showed elevated antimicrobial activity. A synergistic effect was observed in case of five combinations of essential oil. Based on the results, we find that some individual essential oils and mixture compositions (due to synergic effect) could be good candidates for the preservation of fresh vegetables. These preliminary findings suggest that essential oils from locally grown spices could contribute to decreasing the health risk and also to the suppression of emergence of antibiotic resistance.

Antimicrobial Efficacy of Liposome-Encapsulated Citral and Its Effect on the Shelf Life of Shatangju Mandarin

ABSTRACT

Liposome-encapsulated citral was prepared by means of a hot homogenization method. The microstructure, particle size, and zeta potential of the capsules were analyzed by transmission electron microscope and dynamic light scattering, respectively, in which the results showed a good dispersion stability of the citral-loaded liposome. In vitro tests showed that liposome-encapsulated citral significantly (P < 0.05) reduced the populations of Escherichia coli, Bacillus subtilis, Staphylococcus aureus, and Penicillium italicum more than free citral. In vivo tests conducted on fresh Shatangju mandarin showed that liposome-encapsulated citral-treated fruit exhibited a decay incidence of 56.67%, which is 42.04% lower than free citral-treated fruit (97.78%) after 26 days of storage at 25°C and 60 to 70% relative humidity. Additionally, fruit treated with citral-loaded liposome significantly reduced weight loss and viable yeast and mold during storage. In summary, liposome-encapsulated citral could be an effective antimicrobial agent to extend the shelf life of the Shatangju mandarin.

HIGHLIGHTS

In vitro mechanism of antibacterial action of a citrus essential oil on an enterotoxigenic Escherichia coli and Lactobacillus rhamnosus

AIM

This study investigated the in vitro mechanism of action of a commercial citrus EO, Brazilian orange terpenes (BOT), on an enterotoxigenic Escherichia coli (ETEC) isolated from pig gut and on Lactobacillus rhamnosus.

METHODS AND RESULTS

Firstly, bacteria were exposed sequentially to BOT every 3 h (three times) at sub-minimal inhibitory concentrations and results showed that sequential exposure to BOT provoked a higher reduction of bacteria viability than a single exposure and the reduction of ETEC viability was higher compared to that of L. rhamnosus. Then, evaluation of the BOT effects on the cell membrane permeability and integrity, indicated that BOT increased the membrane permeability and caused disruptive effects on the integrity of bacterial cells as reflected by an increase of the relative electric conductivity and the release of essential cell constituents. Interestingly, BOT effects were more pronounced on the ETEC than on L. rhamnosus. This was ratified by scanning electron microscopy, which showed more noticeable morphological damages and disturbances on ETEC cells than on the L. rhamnosus cells. Limonene was detected as the major compound in BOT by polar/nonpolar GC-MS (78·65%/79·38%).

CONCLUSIONS

Results revealed that the probable mechanism of the selective antibacterial action of the citrus EO, BOT, can be described as altering more remarkable the permeability and integrity of the cytoplasmic membrane as well as the external structure of ETEC cells than L. rhamnosus cells.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study provides information about the mechanism of antibacterial action displayed by a citrus EO, a by-product of the citrus processing industry, as a natural alternative to antibiotics used in pig production sector to combat pathogens such as ETECs.

Syzygium aromaticum L. (Myrtaceae): Traditional Uses, Bioactive Chemical Constituents, Pharmacological and Toxicological Activities

Herbal medicinal products have been documented as a significant source for discovering new pharmaceutical molecules that have been used to treat serious diseases. Many plant species have been reported to have pharmacological activities attributable to their phytoconstituents such are glycosides, saponins, flavonoids, steroids, tannins, alkaloids, terpenes, etc. Syzygium aromaticum (clove) is a traditional spice that has been used for food preservation and possesses various pharmacological activities. S. aromaticum is rich in many phytochemicals as follows: sesquiterpenes, monoterpenes, hydrocarbon, and phenolic compounds. Eugenyl acetate, eugenol, and β-caryophyllene are the most significant phytochemicals in clove oil. Pharmacologically, S. aromaticum has been examined toward various pathogenic parasites and microorganisms, including pathogenic bacteria, Plasmodium, Babesia, Theileria parasites, Herpes simplex, and hepatitis C viruses. Several reports documented the analgesic, antioxidant, anticancer, antiseptic, anti-depressant, antispasmodic, anti-inflammatory, antiviral, antifungal, and antibacterial activity of eugenol against several pathogenic bacteria including methicillin-resistant Staphylococcusepidermidis and S. aureus. Moreover, eugenol was found to protect against CCl4-induced hepatotoxicity and showed a potential lethal efficacy against the multiplication of various parasites including Giardia lamblia, Fasciolagigantica, Haemonchuscontortus, and Schistosomamansoni. This review examines the phytochemical composition and biological activities of clove extracts along with clove essential oil and the main active compound, eugenol, and implicates new findings from gas chromatography-mass spectroscopy (GC-MS) analysis.