Recent Advances in the Application of Antibacterial Complexes Using Essential Oils

Fatty acid-modified chitosan and nanoencapsulation of essential oils: A snapshot of applications

Chitosan (CS) and its modification with fatty acid (FA) in addition to the nanoencapsulation with essential oils (EOs) have emerged as promising approaches with diverse applications, particularly in food and fruit preservation. This review aims to curate data on the prospects of CS modified with FA as nanostructures, serving as carriers for EOs and its application in the preservation of fruits. A narrative review with no restricted period was used for the general overview of CS and strategies for its modification with FA. Report on CS modified with FA and nanoencapsulation with EO and their applications were appraised. The prospects of CS modified with FA and EO nanoencapsulation in food and fruit preservation were outlined. Most chitosan-fatty acid (CS-FA) studies have found relevance in water, medical and pharmaceutical industries, with few studies on food preservation. CS-FA formulation with EOs shows substantial potential in preserving fruits and will significantly impact the food industry in the future by extending the shelf life of fruits and reducing food waste.

Chemical Composition and Antibacterial, Antioxidant, and Cytotoxic Activities of Essential Oils from Leaves and Stems of Aeschynomene indica L

The objective of this study was to analyze the chemical composition and evaluate the biological capabilities of the essential oils (EOs) extracted from leaves and stems of wild Aeschynomene indica L. plants by the hydrodistillation method. By using GC-FID/MS, fifty-six and fifty-five compounds, representing 95.1 and 97.6% of the essential oils in the leaves and stems, respectively, were characterized. The predominant constituents of A. indica EOs were (E)-caryophyllene, linalool, viridiflorol, phytol, hexadecanoic acid, trans-verbenol, and α-guaiene. The antibacterial and synergistic activities of the EOs were assessed by microdilution and checkerboard assays. The results revealed a potent inhibition and bactericidal activity against Staphylococcus aureus and Bacillus subtilis with MICs of 0.312-0.625 mg/mL. When combined with traditional antibiotics, the essential oils of A. indica possessed excellent synergistic effects against all tested bacteria. Additionally, the EOs of A. indica leaves showed higher antioxidant activity (IC50 = 0.11 ± 0.01 µg/mL) compared to the stem oil (IC50 = 0.19 ± 0.01 µg/mL) using the ABTS radical scavenging assay. The in vitro cytotoxicity of EOs against human cancer cell lines HepG2, MCF-7, A-549, and HCT-116 was examined, and MTT assays showed that the EOs possessed a significant cytotoxic potential against MCF-7 breast cancer cells, with IC50 values of 10.04 ± 1.82 and 15.89 ± 1.66 μg/mL, and a moderate cytotoxic activity against other tested cells. In conclusion, the A. indica EOs could be considered a potential source of pharmacologically active compounds.

Clinical Evidence on Expansion of Essential Oil-Based Formulation's Pharmacological Activity in Bovine Mastitis Treatment: Antifungal Potential as Added Value

Bovine mastitis, as a significant and prevalent health problem in dairy herds, is primarily attributed to bacterial infections. Yeasts, although considered relatively rare causative agents, have also been associated with mastitis in dairy cattle. Current mastitis treatment predominantly relies on antibiotics, with limited emphasis on antifungal treatment. However, mycotic mastitis is challenging to treat, since these fungi are often resistant to antibiotics and may even utilize them for energy. In the current research, the in vivo antimicrobial activity of the essential oil-based formulation (Phyto-Bomat), as a possible alternative mastitis treatment associated with yeasts, was studied. This study involved a total of 68 animals from two dairy farms with diagnosed mastitis, and three treatment groups were established: conventional antibiotic treatment, Phyto-Bomat treatment, and the combination of both. The findings suggest significant variations in the presence of Candida samples based on the treatment administered, and the most significant difference was noted in cows treated with the combination (Phyto-Bomat and antibiotics). Yet, it is important to note that the results reveal that, regardless of the treatment type, there are statistically significant differences in the presence of Candida samples across the examined time points. These results aim to provide valuable insights into the potential of EOs as an alternative therapy in bovine mastitis, specifically targeting yeasts. Such findings could offer new strategies in the mycotic mastitis control and reducing the occurrence of secondary infections following antibiotic treatment.

Lippia graveolens Essential Oil to Enhance the Effect of Imipenem against Axenic and Co-Cultures of Pseudomonas aeruginosa and Acinetobacter baumannii

This research focuses on assessing the synergistic effects of Mexican oregano (Lippia graveolens) essential oil or carvacrol when combined with the antibiotic imipenem, aiming to reduce the pathogenic viability and virulence of Acinetobacter baumannii and Pseudomonas aeruginosa. The study highlighted the synergistic effect of combining L. graveolens essential oil or carvacrol with imipenem, significantly reducing the required doses for inhibiting bacterial growth. The combination treatments drastically lowered the necessary imipenem doses, highlighting a potent enhancement in efficacy against A. baumannii and P. aeruginosa. For example, the minimum inhibitory concentrations (MIC) for the essential oil/imipenem combinations were notably low, at 0.03/0.000023 mg/mL for A. baumannii and 0.0073/0.000023 mg/mL for P. aeruginosa. Similarly, the combinations significantly inhibited biofilm formation at lower concentrations than when the components were used individually, demonstrating the strategic advantage of this approach in combating antibiotic resistance. For OXA-51, imipenem showed a relatively stable interaction during 30 ns of dynamic simulation of their interaction, indicating changes (<2 nm) in ligand positioning during this period. Carvacrol exhibited similar fluctuations to imipenem, suggesting its potential inhibition efficacy, while thymol showed significant variability, particularly at >10 ns, suggesting potential instability. With IMP-1, imipenem also displayed very stable interactions during 38 ns and demonstrated notable movement and positioning changes within the active site, indicating a more dynamic interaction. In contrast, carvacrol and thymol maintained their position within the active site only ~20 and ~15 ns, respectively. These results highlight the effectiveness of combining L. graveolens essential oil and carvacrol with imipenem in tackling the difficult-to-treat pathogens A. baumannii and P. aeruginosa.

Natural deep eutectic solvents-based green extraction of vanillin: optimization, purification, and bioactivity assessment

The sustainable extraction of natural compounds has recently attracted significant attention. The extraction of high-quality natural vanillin in active form is crucial for its efficient use in various industries, but conventional solvents are not suitable for this purpose. The flammability, volatility, and toxicity of organic solvents can harm extraction personnel, and their waste liquid can cause environmental pollution. Natural deep eutectic solvents (NADES) are cost-effective, environmentally friendly, biodegradable, and non-toxic organic alternative to conventional solvents. In this study, 20 different NADES were tested for the sustainable extraction of natural vanillin. Among these, a DES system composed of choline chloride: 1,4-butanediol: lactic acid exhibited the highest extraction rate (15.9 mg/g). Employing response surface methodology (RSM), optimal extraction conditions were determined, yielding a vanillin content 18.5 mg/g with water content of 33.9%, extraction temperature of 64.6°C, extraction time of 32.3 min, and a solid-liquid ratio of 44.9 mg/mL. Subsequently, the optimized NADES system was then assessed for reusability in extracting vanillin from vanilla pods and kraft lignin over three cycles, retaining 43% of its extraction efficiency and demonstrating potential for waste reduction. Purification of vanillin was achieved through chromatography using a non-polar resin SP700, with ethanol as a desorption eluent and a feed solution pH of 4.0, resulting in the highest vanillin purity. HPLC and GC-MS analyses confirmed purity, while antioxidant activity assays (DPPH and ABTS) showcased significant antioxidant activity of the purified vanillin. Moreover, vanillin exhibited notable antimicrobial activity against a panel of food-borne bacteria. This study introduces an environmentally friendly approach to vanillin extraction highlights using NADES, emphasizing the potential for producing high-quality bioactive vanillin with reduced environmental impact. The applicability of NADES systems extends beyond vanillin, offering a versatile method for extracting diverse natural compounds.

Recent developments in nanoemulsions against spoilage in cold-stored fish: A review

Nanoemulsion-based technology is developing rapidly in the food industry, especially in the design of delivery systems for bioactive compounds. This review presents an in-depth understanding of the composition, function, antibacterial mechanism and successful application of nanoemulsions as preservative agents against fish spoilage. The results showed that the inclusion of bioactive substances in the food-grade nanoemulsions encapsulation system could improve its stability, control its release, inhibit the microbial growth and reproduction through a variety of targets. These nanoemulsions can inhibit fish spoilage via reducing microbial load and retarding the oxidation of proteins and lipids, thereby maintaining quality attributes of fish. In addition, nanoemulsions could be coupled with vacuum package for enhancing microbial destruction, retaining nutritional value and extending the shelf-life of fish. Accordingly, nanoemulsions are suggested as a promising strategy to inhibit fish spoilage.

Assessing Contact Time and Concentration of Thymus vulgaris Essential Oil on Antibacterial Efficacy In Vitro

The overuse and misuse of antibiotics can pose the risk of spreading mutant strains that show antimicrobial resistance (AMR), with negative impacts on the management of bacterial infections and economic implications for healthcare systems. The research and development of natural antibacterial agents could be a priority in the next years to improve a number of effective antibacterial molecules and to reduce the AMR phenomenon and its development. The present study identified the most effective concentration and contact time of Thymus vulgaris L. essential oil (TEO) to obtain bactericidal effects in vitro against different Gram-positive and Gram-negative bacterial strains. Six clinically isolated (wild types) bacterial strains, (Citrobacter freundii, Enterococcus feciorum, Proteus mirabilis, Acinetobacter cioffi, Pseudomonas putrefaciens and Klebsiella pneumoniae) and two ATCCs (Staphylococcus aureus and Streptococcus mutans) were tested after 1 min, 3 min and 5 min of contact with TEO. The preliminary results on S. aureus after 24 h of incubation revealed a TEO concentration of 9.28 mg/mL (w/v) that completely inhibited bacteria growth, keeping cell viability. The total suppression of bacterial growth at all tested contact times was observed for all tested bacterial strains, and the results were confirmed after 48 h of incubation. Bacterial growth suppression was confirmed even with the presence of organic components. These preliminary results showed the in vitro antimicrobial efficacy of TEO against different Gram-positive and Gram-negative bacterial strains. Future studies are necessary to confirm the reproducibility of these results even on other strains and to define the exact molecular mechanisms of EOs in order to consider TEO as a valid alternative to classic antibiotic therapies and subsequently to reduce the occurrence of AMR.

Antioxidant and Antimicrobial Properties and GC-MS Chemical Compositions of Makwaen Pepper (Zanthoxylum myriacanthum) Extracted Using Supercritical Carbon Dioxide

This research aimed to optimize pressure (10-20 MPa) and temperature (45-60 °C) conditions for supercritical fluid extraction (SFE) of Makwaen pepper (Zanthoxylum myriacanthum) extract (ME) in comparison to conventional hydro-distillation extraction. Various quality parameters, including yield, total phenolic compounds, antioxidants, and antimicrobial activities of the extracts, were assessed and optimized using a central composite design. The optimal SFE conditions were found to be 20 MPa at 60 °C, which resulted in the highest yield (19%) and a total phenolic compound content of 31.54 mg GAE/mL extract. IC₅₀ values for DPPH and ABTS assays were determined to be 26.06 and 19.90 μg/mL extract, respectively. Overall, the ME obtained through SFE exhibited significantly better physicochemical and antioxidant properties compared to ME obtained through hydro-distillation extraction. Gas chromatography-mass spectrometry (GC-MS) analysis revealed that beta-pinene was the major component in the ME obtained through SFE (23.10%), followed by d-limonene, alpha-pinene, and terpinen-4-ol at concentrations of 16.08, 7.47, and 6.34%, respectively. On the other hand, the hydro-distillation-extracted ME showed stronger antimicrobial properties than the SFE-extracted ME. These findings suggest that both SFE and hydro-distillation have the potential for extracting Makwaen pepper, depending on the intended purpose of use.

Phytochemical analysis and evaluation of antimicrobial, antioxidant, and antidiabetic activities of essential oils from Moroccan medicinal plants: Mentha suaveolens, Lavandula stoechas, and Ammi visnaga

Mentha suaveolens, Lavandula stoechas, and Ammi visnaga are widely used in Moroccan folk medicine against several pathological disorders, including diabetes and infectious diseases. This work was designed to determine the chemical profile of M. suaveolens (MSEO), L. stoechas (LSEO), and A. visnaga (AVEO) essential oils and assess their antimicrobial, antioxidant, and antidiabetic effects. The volatile components of LSEO, AVEO, and MSEO were analyzed using Gas Chromatography-Mass Spectrometry (GC-MS). The in vitro antidiabetic activity was assessed using α-amylase and α-glucosidase enzymes, while DPPH, FRAP, and β-carotene/linoleic acid methods were used to determine the antioxidant capacity. The antimicrobial activities were investigated using disc diffusion and broth-microdilution assays. GC-MS investigation revealed that the main components were fenchone (29.77 %) and camphor (24.9 %) for LSEO, and linalool (38.29 %) for AVEO, while MSEO was mainly represented by piperitenone oxide (74.55 %). The results of the antimicrobial evaluation showed that all examined essential oils (EOs) had noticeable antimicrobial activity against both bacteria and yeast, especially Micrococcus luteus and Bacillus subtilis. The MIC, MBC, and MFC values were ranged from 0.015 % to 0.5 %. The MBC/MIC and MFC/MIC ratios were less than or equal to 4.0 % (v/v), indicating their noticeable bactericidal and candidacidal efficacy. Moreover, the three EOs showed significant inhibitory effects on α-amylase and α-glucosidase (p < 0.05). It also exerted remarkable activity on FRAP, β-carotene, and DPPH radicals. These findings demonstrated that the tested plants have promising biological activities, validating their ethnomedicinal value and providing potential applications as natural drugs.

Comparative Virucidal Activities of Essential Oils and Alcohol-Based Solutions against Enveloped Virus Surrogates: In Vitro and In Silico Analyses

The large-scale use of alcohol (OH)-based disinfectants to control pathogenic viruses is of great concern because of their side effects on humans and harmful impact on the environment. There is an urgent need to develop safe and environmentally friendly disinfectants. Essential oils (EOs) are generally recognized as safe (GRAS) by the FDA, and many exhibit strong antiviral efficacy against pathogenic human enveloped viruses. The present study investigated the virucidal disinfectant activity of solutions containing EO and OH against DENV-2 and CHIKV, which were used as surrogate viruses for human pathogenic enveloped viruses. The quantitative suspension test was used. A solution containing 12% EO + 10% OH reduced > 4.0 log10 TCID₅₀ (100% reduction) of both viruses within 1 min of exposure. In addition, solutions containing 12% EO and 3% EO without OH reduced > 4.0 log10 TCID₅₀ of both viruses after 10 min and 30 min of exposure, respectively. The binding affinities of 42 EO compounds and viral envelope proteins were investigated through docking analyses. Sesquiterpene showed the highest binding affinities (from -6.7 to -8.0 kcal/mol) with DENV-2 E and CHIKV E1-E2-E3 proteins. The data provide a first step toward defining the potential of EOs as disinfectants.

Efficacy of combined caprylic acid and thymol treatments for inactivation of Listeria monocytogenes on enoki mushrooms in household and food-service establishments

Raw enoki mushroom is a high-risk vector for listeriosis, which led to foodborne outbreaks resulting in four deaths in the United States in 2020. This study aimed to investigate the washing method for the inactivation of L. monocytogenes in enoki mushrooms for household and food service establishments. Five methods of washing fresh agricultural products without using disinfectants were selected: (1) rinsing under running water (2 L/min, 10 min), (2-3) dipping in water (200 ml/20 g) at 22 or 40 °C for 10 min, and using (4) 10% NaCl or (5) 5% vinegar at 22 °C for 10 min. The antibacterial efficacy of each washing method along with the final rinse was tested with enoki mushrooms inoculated with a 3-strain cocktail of L. monocytogenes (ATCC 19111, 19115, 19117; ca. 6 log CFU/g). The 5% vinegar showed a significant difference in antibacterial effect compared to the other treatments except 10% NaCl (P < 0.05), with the maximum elimination of L. monocytogenes by 1.23 log CFU/g. Therefore, a disinfectant for enoki mushrooms that can complement the commonly used washing method was developed using antimicrobials (caprylic acid, CA: 0, 0.20, 0.40%; thymol, TM: 0, 0.075, 0.15%). By combined treatment of 0.40% CA and 0.15% TM at 22 °C for 10 min, L. monocytogenes was completely inactivated (>5.55 log reduction CFU/g) and did not recover after enrichment, although individual treatments of antimicrobials showed low bactericidal effects of <1.50 log reduction CFU/g. The bacterial membrane disintegration induced by the disinfectant was analyzed through flow cytometry. Additionally, the sensory scores (odor and appearance) and color parameters (L*, a*, and b*) of enoki mushrooms treated with the disinfectant were not significantly different from those of enoki mushrooms washed with water (P > 0.05). Our findings suggest a washing disinfectant consisting of low concentrations of CA and TM with synergistic antibacterial effects without quality deterioration that can ensure the safe consumption of raw enoki mushrooms in homes and food service establishments.

Effects of Microencapsulated Essential Oils on Equine Health: Nutrition, Metabolism and Methane Emission

This review examines the available data regarding the positive effects of microencapsulated essential oils (EOs) on the nutrition, metabolism, and possibly the methane emission of horses. A literature review was conducted on the effect of microencapsulated (EOs) on the health of horses. The information comprises articles published in recent years in indexed journals. The results indicate that mixtures of microencapsulated EOs may be beneficial to equine health due to their antimicrobial and antioxidant activity, as well as their effects on enteric methane production, nutrient absorption, and immune system enhancement. Moreover, encapsulation stabilizes substances such as EOs in small doses, primarily by combining them with other ingredients.

Encapsulation Efficiency and Functional Stability of Cinnamon Essential Oil in Modified β-cyclodextrins: In Vitro and In Silico Evidence

Essential oils (EOs) have good natural antioxidant and antimicrobial properties; however, their volatility, intense aroma, poor aqueous solubility, and chemical instability limit their applications in the food industry. The encapsulation of EOs in β-cyclodextrins (β-CDs) is a widely accepted strategy for enhancing EO applications. The complexation of cinnamon essential oil (CEO) with five types of β-CDs, containing different substituent groups (β-CD with primary hydroxyl, Mal-β-CD with maltosyl, CM-β-CD with carboxymethyl, HP-β-CD with hydroxypropyl, and DM-β-CD with methyl), inclusion process behaviors, volatile components, and antioxidant and antibacterial activities of the solid complexes were studied. The CEOs complexed with Mal-β-CD, CM-β-CD, and β-CD were less soluble than those complexed with DM-β-CD and HP-β-CD. Molecular docking confirmed the insertion of the cinnamaldehyde benzene ring into various β-CD cavities via hydrophobic interactions and hydrogen bonds. GC-MS analysis revealed that HP-β-CD had the greatest adaptability to cinnamaldehyde. The CEO encapsulated in β-, Mal-β-, and CM-β-CD showed lower solubility but better control-release characteristics than those encapsulated in DM- and HP-β-CD, thereby increasing their antioxidant and antibacterial activities. This study demonstrated that β-, Mal-β-, and CM-β-CD were suitable alternatives for the encapsulation of CEO to preserve its antioxidant and antibacterial activities for long-time use.

Interactions between Natural Products-A Review

Plant-based natural products have been used as a source for therapeutics since the dawn of civilization. According to the World Health Organization (WHO), more than 80% of the world's population relies on traditional medicine for their primary healthcare. Numerous natural extracts, widely known in Traditional Chinese Medicine, Indian Ayurveda medicine and other practices, have led to the modern discovery and development of new drugs. Plants continuously interact with their environment, producing new compounds and ever-changing combinations of existing ones. Interestingly, some of the compounds have shown lower therapeutic activity in comparison to the extract they were isolated from. These findings suggest that the higher therapeutic activity of the source extract was due to the synergistic effect of several compounds. In other words, the total therapeutic potential of the extract cannot be explained only by the sum of its parts alone. In traditional medicine, most herbal remedies are based on a mixture of plants, and it is the interaction between different constituents that amplifies their therapeutic potential. Considering the significant influence traditional medicine has on human healthcare, knowing and studying the synergistic effect of compounds is paramount in designing smart therapeutic agents.

First Report on the Chemical Composition, Antioxidant Capacity, and Preliminary Toxicity to Artemia salina L. of Croton campinarensis Secco, A. Rosário & PE Berry (Euphorbiaceae) Essential Oil, and In Silico Study

Croton campinarensis Secco, A. Rosário & PE Berry is an aromatic species recently discovered in the Amazon region. This study first reports the chemical profile, antioxidant capacity, and preliminary toxicity to A. salina Leach of the essential oil (EO) of this species. The phytochemical profile of the essential oil was analyzed by gas chromatography (GC/MS) and (GC-FID). The antioxidant capacity of the EO was measured by its inhibition of ABTS^•+ and DPPH^• radicals. Molecular modeling was used to evaluate the mode of interaction of the major compounds with acetylcholinesterase (AChE). The results indicate that the EO yield was 0.24%, and germacrene D (26.95%), bicyclogermacrene (17.08%), (E)-caryophyllene (17.06%), and δ-elemene (7.59%) were the major compounds of the EO sample. The EO showed a TEAC of 0.55 ± 0.04 mM·L^-1 for the reduction of the ABTS^•+ radical and 1.88 ± 0.08 mM·L^-1 for the reduction of the DPPH^• radical. Regarding preliminary toxicity, the EO was classified as toxic in the bioassay with A. salina (LC₅₀ = 20.84 ± 4.84 µg·mL^-1). Through molecular docking, it was found that the majority of the EO components were able to interact with the binding pocket of AChE, a molecular target related to toxicity evaluated in A. salina models; the main interactions were van der Waals and π-alkyl interactions.

Essential Oils Encapsulated in Zeolite Structures as Delivery Systems (EODS): An Overview

Essential oils (EO) obtained from plants have proven industrial applications in the manufacturing of perfumes and cosmetics, in the production and flavoring of foods and beverages, as therapeutic agents in aromatherapy, and as the active principles or excipients of medicines and pharmaceutics due to their olfactory, physical-chemical, and biological characteristics. On behalf of the new paradigm of a more natural and sustainable lifestyle, EO are rather appealing due to their physical, chemical, and physiological actions in human beings. However, EO are unstable and susceptible to degradation or loss. To tackle this aspect, the encapsulation of EO in microporous structures as zeolites is an attractive solution, since these host materials are cheap and non-toxic to biological environments. This overview provides basic information regarding essential oils, including their recognized benefits and functional properties. Current progress regarding EO encapsulation in zeolite structures is also discussed, highlighting some representative examples of essential oil delivery systems (EODS) based on zeolites for healthcare applications or aromatherapy.

Assessment of Chitosan Coating Enriched with Free and Nanoencapsulated Satureja montana L. Essential Oil as a Novel Tool for Beef Preservation

The effect of chitosan coating enriched with free and nanoencapsulated Satureja montana L. essential oil (EO) on microbial, antioxidant and sensory characteristics of beef was analyzed. Different concentrations of free Satureja montana L. EO (SMEO) and nanoparticles (CNPs) were added to chitosan coatings, namely 0.25%, 0.5% and 1%. The beef samples were immersed in the chitosan coatings and stored at +4 °C for 20 days. In this period, the changes in pH value, total viable count (TVC), lactic acid bacteria, psychrophilic bacteria and Pseudomonas spp. were analyzed. The lipid oxidation of beef was determined by the TBAR assay, while sensory analysis was performed by means of the descriptive evaluation method. Generally, the influence of chitosan coating with CNPs on the growth of the tested microorganisms was more pronounced compared to SMEO. Treatment with coating enriched with 1% CNPs resulted in the reduction in TVC and Pseudomonas spp. by 2.4 and 3 log CFU/g, compared to the control, respectively. Additionally, all applied coatings with SMEO and CNPs resulted in the prolonged oxidative stability of the meat The addition of free SMEO created an unnatural aroma for the evaluators, while this odor was neutralized by nanoencapsulation. The durability of color, smell and general acceptability of beef was significantly increased by application of chitosane coatings with the addition of SMEO or SMEO-CNPs, compared to the control. This research indicates the potential application of enriched chitosan coatings in beef preservation in order to improve meat safety and prolong shelf-life.

Preliminary Study on Phytochemical Constituents and Biological Activities of Essential Oil from Myriactis nepalensis Less

In response to the need for novel therapeutic strategies to combat the development of microbial resistance, plant essential oils may represent a promising alternative source. This study set out to characterize the chemical composition and assess the antibacterial potential of Myriactis nepalensis Less. essential oil (MNEO). Essential oil isolated from M. nepalensis by hydrodistillation was analyzed using a GC–MS technique. The antibacterial properties of MNEO alone and combined with antibiotics (chloramphenicol and streptomycin) were tested via the disc diffusion, microbroth dilution, and checkerboard methods. MNEO was represented by oxygenated sesquiterpenes (60.3%) and sesquiterpene hydrocarbons (28.6%), with caryophyllene oxide, spathulenol, humulene epoxide II, β-elemene, neointermedeol, and β-caryophyllene as the main compounds. MNEO exhibited a strong antibacterial effect against Gram-positive bacteria, with MIC and MBC values of 0.039 mg/mL and 0.039–0.156 mg/mL, respectively, and synergistic effects were observed in both combinations with chloramphenicol and streptomycin. Furthermore, the antibiofilm and cytotoxic activities of MNEO were also evaluated. The crystal violet assay was used for quantification of Staphylococcus aureus biofilm formation, and an MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay was conducted to determine cell viability. The results revealed MNEO could dose-dependently inhibit Staphylococcus aureus biofilm formation and possessed potential cytotoxic on both normal and cancer cells (IC50 values from 13.13 ± 1.90 to 35.22 ± 8.36 μg/mL). Overall, the results indicate that MNEO may have promising applications in the field of bacterial infections.

Preparation and Enhanced Antimicrobial Activity of Thymol Immobilized on Different Silica Nanoparticles with Application in Apple Juice

In order to diminish the application limitations of essential oils (EOs) as natural antimicrobial components in the food industry, novel antimicrobial materials were designed and prepared by immobilization of thymol derivatives on silica particles with different morphologies (hollow mesoporous silica nanoparticles, MCM-41, amorphous silica). The structural characteristics of antimicrobial materials were estimated by FESEM, FT-IR, TGA, N2 adsorption-desorption, and small-angle XRD, and the results revealed that both mesoporous silica nanoparticles maintained the orderly structures and had good immobilization yield. Furthermore, the antibacterial performance tests showed that mesoporous silica nanoparticles greatly enhanced the antimicrobial activity of thymol against two representative foodborne bacteria (Escherichia coli and Staphylococcus aureus), and the application of the antimicrobial support was tested in apple juices inoculated with E. coli. The MBC of functionalized mesoporous silica supports was established to be below 0.1 mg/mL against E. coli and S. aureus, which is much lower than that of free thymol (0.3 mg/mL and 0.5 mg/mL against E. coli and S. aureus, respectively). In addition, at a range from 0.05 mg/mL to 0.2 mg/mL, immobilized hollow mesoporous silica nanoparticles (HMSNs) can inhibit the growth of E. coli in apple juice and maintain good sensory properties during 7 days of storage.

Chemical Composition, Antioxidant and Antibacterial Activity of Two Different Essential Oils Against Mastitis Associated Pathogens

Mastitis is one of the most common and costly diseases affecting dairy cows worldwide. Since antibiotic resistance has become a global threat to both animal and human health, it is becoming more urgent to continuously search for new therapeutical alternatives for the control and treatment of bovine mastitis. Hence, our research aimed to test the therapeutic use of two essential oils (EOs) based on their chemical composition, antibacterial and antioxidant potential. The present study was conducted by collecting milk samples from the cows diagnosed with clinical or subclinical mastitis with the aim of isolating and identifying bacterial strains. The antioxidant potential of essential oils of Menthae piperitae (MP) and Melissa officinalis (MO) was evaluated in several in vitro assays. In the MP EO, a total of 38 compounds were identified, with menthol as the dominant compound, whereas in MO EO 51 compounds were identified. Furthermore, the values of minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) have been used to quantitatively measure the antibacterial activity of each essential oil. In accordance with which, MP EO samples exhibited a higher degree of antibacterial activity than MO EO. Thus, EOs have been shown to be promising alternatives to antibiotics because of their availability, biodegradability, and lower risk of side effects as compared with conventional, antimicrobial treatment. Nevertheless, further clinical studies are needed to test the potential role of EOs in treating mastitis in dairy cows.

A Potential “Vitaminic Strategy” against Caries and Halitosis

Streptococcus mutans and Fusobacterium nucleatum are two key bacteria of the oral microbiota. Due to their ability to form biofilms on oral tissues, they are both involved in the onset of the most common oral diseases. F. nucleatum is also the principal producer of hydrogen sulfide (H2S), causative of the awkward bad breath of halitosis. In this study, the oral product Vea® Oris, made by vitamin E and capric/caprylic acid only, was evaluated as a potential treatment for the most common oral diseases. Different concentrations of the product were tested against both S. mutans and F. nucleatum. The effect on planktonic and biofilm growth was investigated for both strains, and for F. nucleatum, the influence on H2S production was evaluated. From our data, the product did not relevantly reduce the planktonic growth of both strains, whereas it validly counteracted biofilm assemblage. Moreover, an interesting trend of H2S reduction was highlighted. Overall, these results suggested, on the one hand, a synergistic antimicrobial–antibiofilm action of two Vea® Oris components and, together, potential modulation activity on H2S production. However, the study should be implemented to confirm these only preliminary findings, certainly extending the panel of tested bacteria and using alternative methods of detection.

Review of trends in essential oils as alternatives to antibiotics in bovine mastitis treatment

Bovine mastitis is an important disease in the dairy industry responsi?ble for the welfare and significant economic losses in dairy cows. The treatment of choice for mastitis is the administration of antibiotics. However, this therapeutic choice has some disadvantages including presence of antibiotics residues in the milk, low cure rate as well as rapid increase in antibiotic-resistant pathogens. Therefore, new alternative approaches to antibiotics were investigated by different groups of researchers in order to find an effective approach for bovine mastitis therapy. This review was conducted in order to analyze different publications on usage of essential oils in relation to bovine mastitis. There are many in vitro studies for evaluating the antimicrobial efficacy of essential oils against many mastitis associated pathogens. In addition, numerous of tested essential oils have shown good efficacy with a wide range of minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs). On the other hand, only several in vivo studies have focused on therapeutic effects of essential oils. Moreover, recent studies indicate the possibility of using essential oils in the fight against biofilm which could be promising fight against bovine mastitis since unsuccessful antibiotic treatment can be associated with the presence of biofilms.

Emerging chitosan-essential oil films and coatings for food preservation - A review of advances and applications

With the rising demand for fresh and ready-to-eat foods, antimicrobial packaging has been developed to control or prevent microbial growth as well as maintain food quality and safety. Chitosan is an advanced biomaterial for antimicrobial packaging to meet the growing needs of safe and biodegradable packaging. The application of natural essential oils as antimicrobial agents effectively controls the growth of spoilage and pathogenic microbes. Thus, chitosan edible coatings and films incorporated with essential oils have expanded the general applications of antimicrobial packaging in food products. This review summarized the effect of essential oils on modifying the physicochemical characteristics of chitosan-based films. Notably, the antimicrobial efficacy of the developed composite films or coatings was highlighted. The advances in the preparation methods and application of chitosan films were also discussed. Broadly, this review will promote the potential applications of chitosan-essential oils composite films or coatings in antimicrobial packaging for food preservation.

Synergistic Antimicrobial Activities of Combinations of Vanillin and Essential Oils of Cinnamon Bark, Cinnamon Leaves, and Cloves

Plant bioactive compounds have antimicrobial and antioxidant activities that allow them to be used as a substitute for synthetic chemical additives in both food and food packaging. To improve its sensory and bactericidal effects, its use in the form of effective combinations has emerged as an interesting possibility in the food industry. In this study, the antimicrobial activities of essential oils (EOs) of cinnamon bark, cinnamon leaves, and clove and the pure compounds vanillin, eugenol, and cinnamaldehyde were investigated individually and in combination against Listeria monocytogenes and Escherichia coli O157:H7. The possible interactions of combinations of pure compounds and EOs were performed by the two-dimensional checkerboard assay and isobologram methods. Vanillin exhibited the lowest antimicrobial activity (MIC of 3002 ppm against L. monocytogenes and 2795 ppm against E. coli O157:H7), while clove and cinnamon bark EOs exhibited the highest antimicrobial activity (402–404 against L. monocytogenes and 778–721 against E. coli O157:H7). For L. monocytogenes, pure compound eugenol, the main component of cinnamon leaves and clove, showed lower antimicrobial activity than EOs, which was attributed to the influence of the minor components of the EOs. The same was observed with cinnamaldehyde, the main component of cinnamon bark EO. The combinations of vanillin/clove EO and vanillin/cinnamon bark EO showed the most synergistic antimicrobial effect. The combination of the EOs of cinnamon bark/clove and cinnamon bark/cinnamon leaves showed additive effect against L. monocytogenes but indifferent effect against E. coli O157:H7. For L. monocytogenes, the best inhibitory effects were achieved by cinnamon bark EO (85 ppm)/vanillin (910 ppm) and clove EO (121 ppm)/vanillin (691 ppm) combinations. For E. coli, the inhibitory effects of clove EO (104 ppm)/vanillin (1006 ppm) and cinnamon leaves EO (118 ppm)/vanillin (979 ppm) combinations were noteworthy. Some of the tested combinations increased the antimicrobial effect and would allow the effective doses to be reduced, thereby offering possible new applications for food and active food packaging.

Laurus nobilis, Salvia sclarea and Salvia officinalis Essential Oils and Hydrolates: Evaluation of Liquid and Vapor Phase Chemical Composition and Biological Activities

Laurus nobilis, Salvia officinalis and Salvia sclarea essential oils (EOs) and hydrolates (HYs) were investigated to define their chemical compositions and biological properties. Gas-chromatography/Mass-spectrometry (GC/MS) and Headspace-GC/MS (HS-GC/MS) techniques were used to characterize the liquid and vapor phase chemical composition of EOs and HYs. 1,8-Cineole (42.2%, 33.5%) and α-pinene (16.7%, 39.0%) were the main compounds of L. nobilis EO; 1,8-cineole (30.3%, 48.4%) and camphor (17.1%, 8.7%) were for S. officinalis EO; linalyl acetate (62.6%, 30.1%) and linalool (11.1%, 28.9%) were for S. sclarea EO for the liquid and vapor phase, respectively. Chemical profile of HYs was characterized by 1,8-cineole (65.1%, 61.4%) as a main constituent of L. nobilis and S. officinalis HYs, while linalool (89.5%) was the main constituent of S. sclarea HY. The antioxidant activity of EOs and HYs was carried out by DPPH and ABTS assays and antimicrobial properties were also investigated by microdilution and the disc diffusion method for liquid and vapor phase against five different bacterial strains such as Escherichia coli ATCC 25922, Pseudomonas fluorescens ATCC 13525 and Acinetobacter bohemicus DSM 102855 among Gram-negative and Bacillus cereus ATCC 10876 and Kocuria marina DSM 16420 among Gram-positive. L. nobilis and S. officinalis EOs demonstrated considerable antibacterial activity, while S. sclarea EO proved to be less effective. Agar diffusion method and vapor phase test showed the EOs activity with the biggest halo inhibition diameters against A. bohemicus and B. cereus. A remarkably high antioxidant activity was determined for L. nobilis showing low EC₅₀ values and also for S. sclarea; good EO results were obtained in both of the used assays. S. officinalis EC₅₀ values were slightly higher to which corresponds to a lower antioxidant activity. Concerning the HYs, the EC₅₀ values for L. nobilis, S. officinalis and S. sclarea were remarkably high corresponding to an extremely low antioxidant activity, as also obtained by expressing the values in Trolox equivalent antioxidant capacity (TEAC).

An Overview of the Potential Therapeutic Applications of Essential Oils

The emergence of antimicrobial resistance (AMR) has urged researchers to explore therapeutic alternatives, one of which includes the use of natural plant products such as essential oils (EO). In fact, EO obtained from clove, oregano, thymus, cinnamon bark, rosemary, eucalyptus, and lavender have been shown to present significant inhibitory effects on bacteria, fungi, and viruses; many studies have been done to measure EO efficacy against microorganisms. The strategy of combinatory effects via conventional and non-conventional methods revealed that the combined effects of EO-EO or EO-antibiotic exhibit enhanced efficacy. This paper aims to review the antimicrobial effects of EO, modes of EO action (membrane disruption, efflux inhibition, increase membrane permeability, and decrease in intracellular ATP), and their compounds' potential as effective agents against bacteria, fungi, and viruses. It is hoped that the integration of EO applications in this work can be used to consider EO for future clinical applications.

Natural Preparations Based on Orange, Bergamot and Clove Essential Oils and Their Chemical Compounds as Antimicrobial Agents

Since ancient times complementary therapies have been based on the use of medicinal plants, natural preparations and essential oils in the treatment of various diseases. Their use in medical practice is recommended in view of their low toxicity, pharmacological properties and economic impact. This paper aims to test the antimicrobial effect of natural preparation based on clove, orange and bergamot essential oils on a wide range of microorganisms that cause infections in humans including: Streptococcus pyogenes, Staphylococcus aureus, Shigella flexneri, Candida parapsilosis, Candida albicans, Pseudomonas aeruginosa, Escherichia coli, Salmonella typhimurium and Haemophilus influenza. Three natural preparations such as one-component emulsions: clove (ECEO), bergamote (EBEO), and orange (EOEO), three binary: E(BEO/CEO), E(BEO/OEO), E(CEO/OEO) and a tertiary emulsion E(OEO/BEO/CEO) were obtained, characterized and tested for antimicrobial effects. Also, the synergistic/antagonistic effects, generated by the presence of the main chemical compounds, were studied in order to recommend a preparation with optimal antimicrobial activity. The obtained results underline the fact that the monocomponent emulsion ECEO shows antimicrobial activity, while EOEO and EBEO do not inhibit the development of the analyzed strains. In binary or tertiary emulsions E(BEO/CEO), E(CEO/OEO) and E(OEO/ BEO/CEO) the antimicrobial effect of clove oil is potentiated due to the synergism exerted by the chemical compounds of essential oils.