Chemical composition, cytotoxicity, antimicrobial and antifungal activity of several essential oils

Phytotherapeutic potential against MRSA: mechanisms, synergy, and therapeutic prospects

BACKGROUND

Rising resistance to antimicrobials, particularly in the case of methicillin-resistant Staphylococcus aureus (MRSA), represents a formidable global health challenge. Consequently, it is imperative to develop new antimicrobial solutions. This study evaluated 68 Chinese medicinal plants renowned for their historical applications in treating infectious diseases.

METHODS

The antimicrobial efficacy of medicinal plants were evaluated by determining their minimum inhibitory concentration (MIC) against MRSA. Safety profiles were assessed on human colorectal adenocarcinoma (Caco-2) and hepatocellular carcinoma (HepG2) cells. Mechanistic insights were obtained through fluorescence and transmission electron microscopy (FM and TEM). Synergistic effects with vancomycin were investigated using the Fractional Inhibitory Concentration Index (FICI).

RESULTS

Rheum palmatum L., Arctium lappa L. and Paeonia suffructicosaas Andr. have emerged as potential candidates with potent anti-MRSA properties, with an impressive low MIC of 7.8 µg/mL, comparable to the 2 µg/mL MIC of vancomycin served as the antibiotic control. Crucially, these candidates demonstrated significant safety profiles when evaluated on Caco-2 and HepG2 cells. Even at 16 times the MIC, the cell viability ranged from 83.3% to 95.7%, highlighting their potential safety. FM and TEM revealed a diverse array of actions against MRSA, such as disrupting the cell wall and membrane, interference with nucleoids, and inducing morphological alterations resembling pseudo-multicellular structures in MRSA. Additionally, the synergy between vancomycin and these three plant extracts was evident against MRSA (FICI < 0.5). Notably, aqueous extract of R. palmatum at 1/4 MIC significantly reduced the vancomycin MIC from 2 µg/mL to 0.03 µg/mL, making a remarkable 67-fold decrease.

CONCLUSIONS

This study unveil new insights into the mechanistic actions and pleiotropic antibacterial effectiveness of these medicinal plants against resistant bacteria, providing robust evidence for their potential use as standalone or in conjunction with antibiotics, to effectively combat antimicrobial resistance, particularly against MRSA.

Essential oils as valuable feed additive: A narrative review of the state of knowledge about their beneficial health applications and enhancement of production performances in poultry

New research has begun to develop safe and effective alternatives to feed-antibiotics as growth enhancers in response to mounting pressure on the poultry sector to do so. There is a significant demand for poultry products all across the world right now. To achieve this goal, key performance indicators are optimized, such as the rate of chicken growth, the amount of feed used, and the health of the flock as a whole. As a result of this growing need, various alternatives to antibiotics have entered the market. New approaches are desperately needed to keep poultry productivity and efficiency at a high level in the face of mounting pressure to limit the use of antibiotics. Recent years have seen an uptick in interest in the potential of aromatic plant extracts as growth and health boosters in poultry. The great majority of plants' positive effects are accounted for by essential oils (EOs) and other secondary metabolites. EOs have been proven to promote digestive secretion production, improve blood circulation, exert antioxidant qualities, reduce levels of dangerous microbes, and maybe improve the immune status of poultry. EOs are often believed to be safe, non-toxic alternatives because they are all-natural, chemical-free, and devoid of potentially harmful deposits. EOs are extracted from plants, and while there are thousands of them, only approximately 300 have been deemed to have significant commercial value. Many different types of bacteria, viruses, fungi, and parasites are negatively affected by EOs in multiple studies conducted both in vitro and in vivo. The review covers the fundamentals of EOs, their anti-oxidant and immunomodulatory capabilities, their growth-promoting benefits, and their effectiveness against numerous diseases in poultry.

Potential effects of essential oils in safeguarding the health and enhancing production performance of livestock animals: The current scientific understanding

The food sector competes in a cutthroat environment, and it constantly struggles to maintain or even grow its market share. For customer confidence and consumption to remain strong, consistent animal products are needed. The qualitative attributes of the derived goods appear to be improved by the addition of bioactive substances to food, such as essential oils (EOs), and consumers are shielded from the impacts of bacterial and oxidative deterioration. Due to the current controversy surrounding synthetic chemicals and their alleged carcinogenic potential, a substantial study has been done to find effective and safe substitutes. Aromatic plants and the corresponding EOs from them are considered natural products and are typically employed in ruminant nutrition. Since dietary supplementation has been demonstrated to be an easy and practical method to successfully suppress oxidative processes or microbial deterioration at their localized sites, the addition of EOs in animal diets is now becoming a regular practice. However, there is just a little amount of evidence supporting the notion that these compounds may improve nutrient absorption and gastrointestinal health. Additionally, a variety of factors affect how well EOs works in animal diets. These variables can be, on the one hand, the erratic composition, and the many additions to the diet, and, on the other hand, erratic animal genetic elements. Maximizing the use of EOs and creating high-quality products require a deeper understanding of the composition and activity of the gastrointestinal tract microbiota. Numerous EOs contain bioactive substances with the potential to serve as multifunctional feed supplements for animals, with impacts on growth performance, the digestive system, the growth of pathogenic bacteria, and lipid oxidation, among others. To establish their regular use in animal production and to determine their precise mechanism of action, more research is required. The potential advantages of EOs for livestock health and production are highlighted in the current article.

Combining Essential Oils with Each Other and with Clotrimazole Prevents the Formation of Candida Biofilms and Eradicates Mature Biofilms

Fungal infections by Candida spp. are opportunistic and most often occur in individuals with some predisposing factor. Essential oils (EO) have anti-Candida potential, being a therapeutic alternative to be explored, especially for superficial and mucosal candidiasis. The objective was to analyze the synergistic potential between the EO of Citrus limon, Cupressus sempervirens, Litsea cubeba and Melaleuca alternifolia, and each of them with clotrimazole, to inhibit in vitro the formation and eradication of Candida spp. biofilms. Added to this, the survival of Caenorhabditis elegans was evaluated after exposure to EO, clotrimazole and their synergistic combinations. Anti-Candida activity was determined by microdilution for the substances alone and in EO−EO and EO−clotrimazole combinations. The combinations were performed by the checkerboard method, and the reduction in the metabolic activity of biofilms was determined by the viability of MTT/menadione. C. elegans larvae survival was evaluated after 24 h of exposure to EO, clotrimazole and synergistic combinations. The minimum inhibitory concentration (MIC) of EO ranged from 500 to >4000 µg/mL. The lowest MIC (500 µg/mL) was for C. sempervirens and L. cubeba on a C. krusei isolate; for clotrimazole, the MIC ranged from 0.015 to 0.5 µg/mL. Biofilm inhibition and eradication both ranged from 1000 to >4000 µg/mL. The lethal concentration (LC50) of C. limon, L. cubeba and M. alternifolia was 2000 µg/mL for C. elegans, while for C. sempervirens and clotrimazole, it was not determined within the concentration limits tested. In combination, more than 85% of the larvae survived M. alternifolia−clotrimazole, M. alternifolia−L. cubeba, C. sempervirens−clotrimazole and C. sempervirens−C. limon combinations. This study is the first, to our knowledge, to present a synergistic relationship of EO−EO and EO−clotrimazole combinations on Candida spp. biofilms.

Vapor-Phase of Essential Oils as a Promising Solution to Prevent Candida Vaginal Biofilms Caused by Antifungal Resistant Strains

Background: Vulvovaginal candidiasis (VVC) is a disease with high incidence, a huge impact on the quality of life and health of women, and which represents a great challenge to treat. The growing need to apply antifungal intensive therapies have contributed to an emergence of drug-resistant Candida strains. Thus, effective therapeutic options, to meet the antifungal-resistance challenge and to control high resilient biofilms, are urgently needed. This study aimed to investigate the antifungal activity of essentials oils (EOs) on drug-resistant Candida vaginal isolates. Method: Therefore, the antimicrobial effect of tea tree, niaouli, white thyme, and cajeput EOs on the planktonic growth of Candida isolates was initially evaluated by an agar disc diffusion method. Then, the vapor-phase effect of tea tree EO (VP-TTEO) on biofilm formation and on pre-formed biofilms was evaluated by crystal violet staining, XTT reduction assay, colony forming units’ enumeration, and scanning electron microscopy. Results: The results revealed high antifungal activity of EOs against drug-resistant Candida isolates. Additionally, the VP-TTEO showed a significant inhibitory effect on the biofilm formation of all tested isolates and was able to provoke an expressive reduction in mature Candida albicans biofilms. Conclusions: Overall, this study suggests that the VP-EO may be a promising solution that is able to prevent biofilm-related VVC caused by antifungal-resistant strains.

Chemical composition and biological activity of Peucedanum dhana A. Ham essential oil

The essential oil was extracted from Peucedanum dhana A. Ham, which grows in Thailand, using a Clevenger apparatus, resulting in an oil yield of 0.76% w/w. Forty-two compounds were identified using gas chromatography-mass spectrometry. The major compounds were trans-piperitol (51.23%), β-pinene (11.72%), o-cymene (11.12%), γ-terpinene (9.21%), and limonene (4.91%). The antimicrobial activity of the P. dhana essential oil was investigated by measuring the inhibition zone diameter, minimum inhibitory concentration (MIC), and minimum microbicidal concentration (MMC). The inhibition zone diameters of P. dhana essential oil (1000 µg/mL) against tested pathogens ranged from 10.70 to 40.80 mm. Significant antimicrobial activity against tested pathogens was obtained, with MIC and MMC values of 62.50–250 µg/mL and 250–1000 µg/mL, respectively. Escherichia coli, Pseudomonas aeruginosa, and Enterobacter aerogenes exposed to P. dhana essential oil at the MIC were analysed by flow cytometry using propidium iodide (PI) and SYTO9 to assess membrane integrity compared to trans-piperitol and β-pinene. After 24 h, treatments with trans-piperitol resulted in the most significant cell membrane alteration and depolarization followed by P. dhana essential oil and β-pinene, respectively. It was demonstrated that the P. dhana essential oil presented antibacterial action against E. coli, P. aeruginosa, and E. aerogenes. The antioxidant activity of P. dhana essential oil was measured using 2,2-diphenyl-2-picrylhydrazyl (DPPH) and 2,2-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium (ABTS) scavenging activity assays. The IC₅₀ values obtained from the DPPH and ABTS methods were 9.13 and 9.36 mg/mL, respectively. The cytotoxic effect of P. dhana oil was tested against human colonic adenocarcinoma (SW480), human lung adenocarcinoma (A549), cervical cancer (Hela), and murine fibroblast (3T3L1) cells using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The essential oil had cytotoxicity against all cancer cells, with significant cytotoxicity towards SW480 cells. As a control experiment, two pure compounds—trans-piperitol and β-pinene, were also tested for their antimicrobial, antioxidant, and cytotoxic activity. Both compounds showed varied activity in all assays. The results indicate that P. dhana essential oil could be used as a source of functional ingredients in food and pharmaceutical applications.

Phytochemical Compositions and Biological Activities of Essential Oils from the Leaves, Rhizomes and Whole Plant of Hornstedtia bella Škorničk

The rapid emergence of drug-resistant strains and novel viruses have motivated the search for new anti-infectious agents. In this study, the chemical compositions and cytotoxicity, as well as the antibacterial, antifungal, antitrichomonas, and antiviral activities of essential oils from the leaves, rhizomes, and whole plant of Hornstedtia bella were investigated. The GC/MS analysis showed that β-pinene, E-β-caryophyllene, and α-humulene were found at high concentrations in the essential oils. The essential oils exhibited (i) inhibition against Staphylococcus aureus, methicillin-resistant Staphylococcus aureus, Staphylococcus epidermidis with minimum inhibitory concentrations (MIC) and minimum lethal concentration (MLC) values from 1 to 4% (v/v); (ii) MIC and MLC values from 2 to 16% (v/v) in Candida tropicalis and Candida parapsilosis; (iii) MIC and MLC values from 4 to 16% in Enterococcus faecalis; and (iv) MIC and MLC values from 8 to greater than or equal to 16% (v/v) in the remaining strains, including Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Candida albicans, and Candida glabrata. In antitrichomonas activity, the leaves and whole-plant oils of Hornstedtia bella possessed IC₅₀, IC₉₀, and MLC values of 0.008%, 0.016%, and 0.03% (v/v), respectively, whilst those of rhizomes oil had in turn, 0.004%, 0.008%, and 0.016% (v/v).Besides, the leaf oil showed a weak cytotoxicity against Vero 76 and MRC-5; meanwhile, rhizomes and whole-plant oils did not exert any toxic effects on cell monolayers. Finally, these oils were not active against EV-A71.

Biological Activities of Essential Oils from Leaves of Paramignya trimera (Oliv.) Guillaum and Limnocitrus littoralis (Miq.) Swingle

The present study aimed to determine the bioactivities of essential oils extracted from the leaves of Paramignya trimera and Limnocitrus littoralis, including cytotoxicity, antiviral, antibacterial, antimycotic, and antitrichomonas effects. Herein, it was indicated that P. trimera and L. littoralis oils showed no cytotoxicity on normal cells, namely MT-4, BHK-21, MDBK, and Vero-76. P. trimera oil (i) exhibited the strongest inhibition against Staphylococcus aureus with MIC and MLC values of 2% (v/v); (ii) showed MIC and MLC values of 8% (v/v) in Candida parapsilosis; and (iii) in the remaining strains, showed MIC and MLC values greater than or equal to 16% (v/v). On the other hand, L. littoralis oil (i) displayed the strongest inhibition against Candida tropicalis and Candida parapsilosis with 2% (v/v) of MIC and MLC; and (ii) in the remaining strains, possessed MIC and MLC greater than or equal to 16% (v/v). In addition, antitrichomonas activities of the oils were undertaken, showing IC₅₀, IC₉₀, MLC values, respectively, at 0.016%, 0.03%, and 0.06% (v/v) from P. trimera, and 0.03%, 0.06%, 0.12% (v/v) from L. littoralis, after 48 h of incubation. The oils were completely ineffective against ssRNA+ (HIV-1, YFV, BVDV, Sb-1, CV-B4), ssRNA- (RSV, VSV), dsRNA (Reo-1), and dsDNA (HSV-1, VV) viruses. This is the first report describing the cytotoxicity, antiviral, antibacterial, antimycotic, and antitrichomonas activities of the essential oils of P. trimera and L. littoralis.

In-Vitro Evaluation of 52 Commercially-Available Essential Oils Against Leishmania amazonensis

Leishmaniasis is a neglected tropical disease caused by members of the Leishmania genus of parasitic protozoa that cause different clinical manifestations of the disease. Current treatment options for the cutaneous disease are limited due to severe side effects, poor efficacy, limited availability or accessibility, and developing resistance. Essential oils may provide low cost and readily available treatment options for leishmaniasis. In-vitro screening of a collection of 52 commercially available essential oils has been carried out against promastigotes of Leishmania amazonensis. In addition, cytotoxicity has been determined for the essential oils against mouse peritoneal macrophages in order to determine selectivity. Promising essential oils were further screened against intracellular L. amazonensis amastigotes. Three essential oils showed notable antileishmanial activities: frankincense (Boswellia spp.), coriander (Coriandrum sativum L.), and wintergreen (Gualtheria fragrantissima Wall.) with IC₅₀ values against the amastigotes of 22.1 ± 4.2, 19.1 ± 0.7, and 22.2 ± 3.5 μg/mL and a selectivity of 2, 7, and 6, respectively. These essential oils could be explored as topical treatment options for cutaneous leishmaniasis.

Influence of six essential oils on invasive Solidago canadensis L. seed germination

Solidago canadensis L. (SC) (Canadian goldenrod) is a dangerous plant invader in Europe, which suppress the indigenous flora. Essential oils (EOs) are considered biological control agents. GC-MS analysis for identification of main components was conducted and the potential phytotoxicity of six EOs were also evaluated. Limonene and β-thujone were dominant components in Salvia officinalis L., menthone and menthol in Mentha × piperita L., carvacrol in Origanum vulgare L., estragole/anisole and anethole in Foeniculum vulgare Mill., limonene and carvone in Anethum graveolens L., and anethole in Pimpinella anisum L. Along with EOs, anethole, anisole, camphor, carvone, estragole, limonene, menthol, menthone, thujone and thymol were used independently to evaluate phytotoxic effect against Canadian goldenrod seed germination. A significant inhibitory effect was registered for origanum (1.250 µg.ml^-1). The influence of single components was significant. The highest phytotoxic activity was registered with anethole and estragole. Phenolic compounds were the inhibitoriest, followed by oxygenated and hydrocarbon monoterpenes.

Potential of Borojoa patinoi Cuatrecasas water extract to inhibit nosocomial antibiotic resistant bacteria and cancer cell proliferation in vitro

Borojó (Borojoa patinoi Cuatrec.) is a fruit used in Colombian traditional medicine with supposed antihypertensive, antitumoral, diuretic, healing, immunological, anti-inflammatory and aphrodisiac effects. To explore the relative merits in terms of biological activities of borojó aqueous extract (BAE), we investigated in vitro its antimicrobial activity on nosocomial pathogenic and multidrug resistant (MDR) strains of Pseudomonas aeruginosa (6), Staphylococcus aureus (1) and Candida species (6), as well as its cytotoxicity on human conjunctive Wong-Kilbourne derivative (WKD) cells and Caco-2 cells from heterogeneous human epithelial colorectal adenocarcinoma. The bacteriostatic activity was observed overall on P. aeruginosa strains, as evidenced by the increase of the lag phase (43 hours) and reduction of the maximum growth rate detected using 187.5 mg BAE per mL. The bactericidal activity, instead, was observed at 375 mg BAE per mL. On the other hand, BAE showed an anti-proliferative effect against the Caco-2 cell line and was shown to be toxic on the WKD cell line at concentrations ranging from 0.05 to 187.5 μg mL-1. The analysis of the phenolic fraction of the fruit aqueous extract (BAE) using UHPLC-MS/MS showed the presence of 26 compounds, with vanillic, syringic and o-coumaric acids as the most abundant. Among these molecules, 7.81 ng mL-1 luteolin and myricetin, singly tested, were able to reduce bacterial growth. To the best of our knowledge, we are unaware of any previous studies demonstrating the anti-bacterial activity of borojó aqueous extract against antibiotic resistant strains of P. aeruginosa, and its anti-proliferative effect against WKD and Caco-2 cell lines. The latter result offers a potential base for new interest and investigations in relation to colon carcinoma models and borojó fruit consumption, since in Colombia this fruit is consumed also for its supposed antitumoral effects.

Attenuation of Listeria monocytogenes Virulence by Cannabis sativa L. Essential Oil

Anti-virulence strategies are being explored as a novel approach to combat pathogens. Such strategies include inhibition of surface adhesion, tissue invasion, toxin production, and/or interference with the gene regulation of other virulence traits. Listeria monocytogenes, the causative agent of listeriosis, is a facultative intracellular food pathogen characterized by a wide distribution in the environment. Its ability to persist within biofilms and to develop resistance to sanitizers is the cause of significant problems in food processing plants and of steep costs for the food industry. In humans, the treatment of listeriosis is hampered by the intracellular location of listeriae and the poor intracellular penetration of some antibiotics. Eleven L. monocytogenes isolates from patients who were diagnosed with invasive listeriosis in Italy in 2014-2016 were studied. This in vitro and in vivo study explored the antibacterial and anti-virulence properties of a steam-distilled essential oil of Cannabis sativa L., which is being intensively investigated for its high content in powerful bioactive phytochemicals. Susceptibility experiments demonstrated a moderate bactericidal activity of the essential oil (Minimum Bactericidal Concentration > 2048 μg/mL). Assessment of the effects of sublethal concentrations of the essential oil on L. monocytogenes virulence traits demonstrated a significant action on motility. Listeriae were non-motile after exposure to the essential oil. Light and scanning electron microscopy documented aggregates of listeriae with the flagella trapped inside the cluster. Real-time RT-PCR experiments showed downregulation of flagellar motility genes and of the regulatory gene prfA. The ability to form biofilm and to invade Caco-2 cells was also significantly reduced. Galleria mellonella larvae infected with L. monocytogenes grown in presence of sublethal concentrations of the essential oil showed much higher survival rates compared with controls, suggesting that the extract inhibited tissue invasion. Food contamination with L. monocytogenes is a major concern for the food industry, particularly for plants making ready-to-eat and processed food. The present work provides a baseline in the study of the anti-virulence properties of the C. sativa essential oil against L. monocytogenes. Further studies are needed to understand if it could be used as an alternative agent for the control of L. monocytogenes in food processing plants.

Use of Pinus sylvestris L. (Pinaceae), Origanum vulgare L. (Lamiaceae), and Thymus vulgaris L. (Lamiaceae) essential oils and their main components to enhance itraconazole activity against azole susceptible/not-susceptible Cryptococcus neoformans strains

Background

Cryptococcal infections, besides being a problem for immunocompromised patients, are occasionally being a problem for immunocompetent patients. In addition, the lower susceptibility of this yeast to azoles is a growing problem in health care. To date, there are very few molecules with any activity towards Cryptococcus neoformans, leading to heightened interest in finding new alternatives or adjuvants to conventional drugs for the treatment of mycosis caused by this yeast. Since the essential oils (EOs) are considered as a potential rich source of bioactive antimicrobial compounds, we evaluated the antifungal activity of Origanum vulgare (oregano), Pinus sylvestris (pine), and Thymus vulgaris (thyme red) EOs, and their components (α-pinene, carvacrol, thymol) compared with fluconazole, itraconazole, and voriconazole, against C.neoformans clinical strains. Then, we investigated the effect of EOs and components in combination with itraconazole.

Methods

EO composition was analysed by Gas chromatography-mass spectrometry (GC-MS). A broth microdilution method was used to evaluate the susceptibility of C.neoformans to azoles, EOs and components. Checkerboard tests, isobolograms and time-kill assays were carried out for combination studies.

Results

Six C.neoformans isolates were susceptible to azoles, while one C.neoformans exhibited a reduced susceptibility to all tested azole drugs. All EOs exerted a good inhibitory activity against all C.neoformans strains. Pine EO was the most effective. Among components, thymol exerted the most remarkable activity. By checkerboard testing and isobolographic analysis, combinations of itraconazole with oregano, pine, or thyme EOs, and carvacrol were found to be synergistic (FICI≤0.5) against azole susceptible C.neoformans. Regarding the azole not susceptible C.neoformans strain, the synergistic effect with itraconazole was observed with thyme EO (chemotype: thymol 26.52%; carvacrol 7.85%), and carvacrol. Time-kill assays confirmed the synergistic effects of itraconazole and oregano or thyme EO against azole susceptible C.neoformans. Binary mixtures of itraconazole/thyme EO or carvacrol yielded additive effects on the azole not susceptible C.neoformans.

Conclusions

Our findings highlight the potential effectiveness of thyme, oregano EOs, and carvacrol as natural and cost-effective adjuvants when used in combination with itraconazole. Identification of EOs exerting these effects could be one of the feasible ways to overcome drug resistance, reducing drug concentration and side effects.

In vitro evaluation of the amoebicidal activity of rosemary (Rosmarinus officinalis L.) and cloves (Syzygium aromaticum L. Merr. & Perry) essential oils against Acanthamoeba polyphaga trophozoites

Several species of the genus Acanthamoeba cause human diseases. Treatment of infections involves various problems, emphasising the need to develop alternative antiprotozoal agents. We studied the anti-amoebic activity of Essential Oils (EOs), derived from rosemary (Rosmarinus officinalis L.) and cloves (Syzygium aromaticum L. Merr. & Perry), against Acanthamoeba polyphaga strain. The amoebicidal activity of cloves and rosemary EOs was preliminary demonstrated by the morphology change (modifications in the cell shape, the presence of precipitates in the cytoplasm, autophagic vesicles, membrane blends) of the treated trophozoites. The cell-counts, carried out after staining trophozoites with a Trypan blue solution, revealed that both EOs were active in a dose-dependent manner and in relation to the exposure time. This activity was evident after few hours, with encouraging results obtained in particular with cloves EO, able to act at the lower concentrations and after 1 h, probably for its high eugenol content (65.30%).

Antimicrobial activity of Austroeupatorium inulaefolium (H.B.K.) against intracellular and extracellular organisms

The antimicrobial activity of Austroeupatorium inulaefolium (H.B.K.) essential oil was studied in different pathogens species and its cytotoxicity activity was determinated on different cellular lines. Despite the good antibacterial activity of A. inulaefolium, it has been cytotoxic at low concentrations. Consequently it might be interesting to determine the antimicrobial activity and cytotoxicity of the major compounds of this essential oil.