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Essential Oils as Antimicrobial and Anti-infectious Agents
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Essential Oils as Antimicrobial and Anti-infectious Agents

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Natural Products Chemistry".

Deadline for manuscript submissions: closed (20 July 2018) | Viewed by 151327

Special Issue Editors

Dr. Daniela Rigano

E-Mail Website
Guest Editor
Department of Pharmacy, School of Medicine and Surgery, University of Naples Federico II, Via D. Montesano 49, 80131 Naples, Italy
Interests: natural products; secondary metabolites; structure elucidation; essential oils; NMR spectroscopy; GC-MS and LC-MS
Special Issues, Collections and Topics in MDPI journals
Dr. Adriana Basile

E-Mail Website
Guest Editor
Department of Biology, University of Naples Federico II, 80126 Naples, Italy
Interests: plant natural products; secondary metabolites; antibacterial activity; antioxidant activity; antitumoral activity; microscopy; protection against environmental stresses
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

In last few decades, infectious diseases have continued to be a major health concern worldwide, causing important epidemiological, financial, and logistical implications. The use of many conventional drugs is hampered by a lack of efficacy, emergence of resistance, adverse effects, and high costs. Thus, new strategies and therapeutic alternatives are required: Essential oils (EOs) are, today, considered as an important source for new natural antimicrobials, particularly on multidrug-resistant bacteria, pathogenic fungi, viruses, and parasites. Considering the wide variety of chemical compounds occurring in EOs, it is likely that their antimicrobial activities are attributable to the combination of several mechanisms of action on different parts of the microbial cell, and this is probably the reason why bacteria do not develop resistance. EOs may provide an interesting option to replace the use of conventional antimicrobials with a low cost and safe medicinal, or could be used in addition to them in order to decrease their potential risk of toxicity.

This Special Issue aims to attract contributions on all aspects of the chemistry and antimicrobial activity of essential oils. There is still the challenge to further explore the range of their biological effects and their potential applications as antibiotic and anti-infectious agents.

Prof. Dr. Daniela Rigano
Prof. Dr. Adriana Basile
Guest Editors

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Keywords

  • essential oils
  • antimicrobials
  • bacterial infections
  • fungi
  • viruses
  • parasites
  • resistance

Published Papers (20 papers)

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14 pages, 832 KiB  
Article
High Potency of Melaleuca alternifolia Essential Oil against Multi-Drug Resistant Gram-Negative Bacteria and Methicillin-Resistant Staphylococcus aureus
by Alessandra Oliva, Silvia Costantini, Massimiliano De Angelis, Stefania Garzoli, Mijat Božović, Maria Teresa Mascellino, Vincenzo Vullo and Rino Ragno
Molecules 2018, 23(10), 2584; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules23102584 - 09 Oct 2018
Cited by 68 | Viewed by 9873
Abstract
Purpose: Herein, an extended investigation of Tea tree oil (TTO) against a number of multi-drug resistant (MDR) microorganisms in liquid and vapor phases is reported. Methods: The activity of TTO was tested against methicillin-sensitive Staphylococcus aureus (MSSA), Escherichia coli, and clinical strains [...] Read more.
Purpose: Herein, an extended investigation of Tea tree oil (TTO) against a number of multi-drug resistant (MDR) microorganisms in liquid and vapor phases is reported. Methods: The activity of TTO was tested against methicillin-sensitive Staphylococcus aureus (MSSA), Escherichia coli, and clinical strains of methicillin-resistant S. aureus (MRSA), extended-spectrum beta lactamases producer carbapenem-sensitive Klebsiella pneumoniae (ESBL-CS-Kp), carbapenem-resistant K. pneumoniae (CR-Kp), Acinetobacter baumannii (CR-Ab), and Pseudomonas aeruginosa (CR-Pa). Minimal inhibitory/bactericidal concentrations (MIC/MBCs) and synergistic activity between TTO and different antimicrobials were determined. In the vapor assay (VP), TTO-impregnated discs were placed on the lid of a petri dish and incubated for 24 h at 37 °C. Results: TTO showed a potent bactericidal activity against all the tested microorganisms. TTO in combination with each reference antimicrobial showed a high level of synergism at sub-inhibitory concentrations, particularly with oxacillin (OXA) against MRSA. The VP assay showed high activity of TTO against CR-Ab. Conclusion: Evaluation of in-vitro activity clearly indicated TTO as a potential effective antimicrobial treatment either alone or in association with known drugs against MDR. Therefore, TTO could represent the basis for a possible role in non-conventional regimens against S. aureus and Gram-negative MDR. TTO in VP might represent a promising option for local therapy of pneumonia caused by CR-Ab. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents)
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16 pages, 1817 KiB  
Article
Origanum vulgare L. Essential Oil as a Potential Anti-Acne Topical Nanoemulsion—In Vitro and In Vivo Study
by Mohammed H. Taleb, Nourtan F. Abdeltawab, Rehab N. Shamma, Sherein S. Abdelgayed, Sarah S. Mohamed, Mohamed A. Farag and Mohammed A. Ramadan
Molecules 2018, 23(9), 2164; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules23092164 - 28 Aug 2018
Cited by 73 | Viewed by 15015
Abstract
Antibiotics are often prescribed in acne treatment; however, Propionibacterium acnes and Staphylococcus epidermidis, the two of the major acne-associated bacteria, developed antibiotic resistance. Essential oils (EOs) present a natural, safe, efficacious and multifunctional alternative treatment. This study aimed to assess the potential [...] Read more.
Antibiotics are often prescribed in acne treatment; however, Propionibacterium acnes and Staphylococcus epidermidis, the two of the major acne-associated bacteria, developed antibiotic resistance. Essential oils (EOs) present a natural, safe, efficacious and multifunctional alternative treatment. This study aimed to assess the potential anti-acne activity of selected seven EOs commonly used in Mediterranean folk medicine. Antimicrobial activity screening of these oils showed oregano to exhibit the strongest antimicrobial activity with minimum inhibitory concentration (MIC) of 0.34 mg/mL and minimum bactericidal concentration (MBC) of 0.67 mg/mL against P. acnes; and MIC of 0.67 mg/mL and MBC of 1.34 mg/mL against S. epidermidis. The composition of the most effective EOs (oregano and thyme) was determined using gas chromatography-mass spectrometry (GC-MS). Monoterpenoid phenols predominated oregano and thyme EO with thymol percentile 99 and 72, respectively. Thymol showed MIC 0.70 mg/mL against both P. acnes and S. epidermidis whereas MBC was 1.40 and 2.80 mg/mL against P. acnes and S. epidermidis, respectively. Moreover, oregano exhibited the strongest anti-biofilm effect against S. epidermidis with MBIC 1.34 mg/mL and killing dynamic time of 12 and 8 h against P. acnes and S. epidermidis, respectively. Oregano, the most effective EO, was formulated and tested as a nanoemulsion in an acne animal mouse model. The formulation showed superior healing and antimicrobial effects compared to the reference antibiotic. Collectively, our data suggested that oregano oil nanoemulsion is a potential natural and effective alternative for treating acne and overcoming the emerging antibiotic resistance. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents)
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11 pages, 3372 KiB  
Article
Anti-Quorum Sensing Activity of 12 Essential Oils on chromobacterium violaceum and Specific Action of cis-cis-p-Menthenolide from Corsican Mentha suaveolens ssp. Insularis
by Jean-Pierre Poli, Elodie Guinoiseau, Dominique De Rocca Serra, Sylvain Sutour, Mathieu Paoli, Félix Tomi, Yann Quilichini, Liliane Berti and Vannina Lorenzi
Molecules 2018, 23(9), 2125; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules23092125 - 23 Aug 2018
Cited by 44 | Viewed by 5612
Abstract
Quorum sensing (QS) is a bacterial communication mechanism used to express various survival or virulence traits leading to enhanced resistance. Chromobacterium violaceum is a commonly used strain that highlights anti-QS action of bioactive substances. Here, we wanted to see if 12 selected essential [...] Read more.
Quorum sensing (QS) is a bacterial communication mechanism used to express various survival or virulence traits leading to enhanced resistance. Chromobacterium violaceum is a commonly used strain that highlights anti-QS action of bioactive substances. Here, we wanted to see if 12 selected essential oils (EO) could exert anti-QS activity. We measured the sublethal minimal QS inhibitory concentration (MQSIC) by assessing violacein production of C. violaceum along with bacterial growth. To confirm the QS disruption, we also proceed to surface bacterial observations using scanning electron microscopy (SEM). We showed that cis-cis-p-menthenolide extracted and isolated from a plant endemic to occidental Mediterranean Sea islands, Mentha suaveolens ssp. insularis, acts as an inhibitor of violacein production and biofilm formation. Measured MQSIC was much lower than the minimal inhibitory concentration (MIC): 0.10 mg·mL−1 vs. 3.00 mg·mL−1. Moreover, disturbance of QS-related traits was confirmed by the degradation of C. violaceum biofilm matrix. There is a clear structure–activity relationship between cis-cis-p-menthenolide and anti-QS activity. Indeed, its isomer molecule (mintlactone) exerts a poor anti-QS action. These results indicate that inhibition of violacein production and biofilm formation by cis-cis-p-menthenolide might be related to a disruption in the QS mechanism. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents)
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18 pages, 4449 KiB  
Article
Antifungal Activity of Essential Oil Compounds (Geraniol and Citral) and Inhibitory Mechanisms on Grain Pathogens (Aspergillus flavus and Aspergillus ochraceus)
by Xi Tang, Ye-Lin Shao, Ya-Jie Tang and Wen-Wen Zhou
Molecules 2018, 23(9), 2108; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules23092108 - 22 Aug 2018
Cited by 108 | Viewed by 6343
Abstract
The grain contamination by Aspergillus spp. has been a serious issue. This study exhibited the excellent antifungal effects of the essential oil compounds (EOCs) geraniol and citral against common grain pathogens (A. flavus and A. ochraceus) in vitro and in situ. [...] Read more.
The grain contamination by Aspergillus spp. has been a serious issue. This study exhibited the excellent antifungal effects of the essential oil compounds (EOCs) geraniol and citral against common grain pathogens (A. flavus and A. ochraceus) in vitro and in situ. The inhibitory mechanisms were also evaluated from the perspective of cell membrane permeability, reactive oxygen species (ROS) generation, and Aspergillus spp. growth-related gene expression. Meanwhile, the combined effects of EOCs in the vapor phase and modified atmosphere packaging (MAP) were examined to find an alternative preservation method for controlling Aspergillus spp. The results indicated that citral exhibited the antifungal activity mainly by downregulating the sporulation- and growth-related genes for both pathogens. Geraniol displayed inhibitory effectiveness against A. flavus predominantly by inducing the intracellular ROS accumulation and showed toxicity against A. ochraceus principally by changing cell membrane permeability. Furthermore, the synthetic effects of EOCs and MAP (75% CO2 and 25% N2) induced better grain quality than the current commercial fumigant AlP. These findings reveal that EOCs have potential to be a novel grain preservative for further application. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents)
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13 pages, 4711 KiB  
Article
Effect of Heat Stress on Yield, Monoterpene Content and Antibacterial Activity of Essential Oils of Mentha x piperita var. Mitcham and Mentha arvensis var. piperascens
by Milad Heydari, Anna Zanfardino, Alireza Taleei, Ali Akbar Shahnejat Bushehri, Javad Hadian, Viviana Maresca, Sergio Sorbo, Michela Di Napoli, Mario Varcamonti, Adriana Basile and Daniela Rigano
Molecules 2018, 23(8), 1903; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules23081903 - 30 Jul 2018
Cited by 45 | Viewed by 5816
Abstract
Heat stress affects the yield of medicinal plants and can reduce biomass and/or metabolite production. In order to evaluate the effect of heat-induced stress on the essential oil production in Mentha x piperita L. var. Mitcham (Mitcham mint) and Mentha arvensis var. piperascens [...] Read more.
Heat stress affects the yield of medicinal plants and can reduce biomass and/or metabolite production. In order to evaluate the effect of heat-induced stress on the essential oil production in Mentha x piperita L. var. Mitcham (Mitcham mint) and Mentha arvensis var. piperascens Malinv. ex L. H. Bailey (Japanese mint), we studied the chemical composition of the oils of the two mint species under different heat shock stresses in growth chambers. The antibacterial activity of the essential oils was also evaluated; microscopic observation (fluorescence and electron transmission) was used to assess the effect of the tested samples on bacterial growth. The results obtained shed light on the mint essential oils composition and biological activity in relation to heat stress. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents)
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12 pages, 262 KiB  
Article
Antimicrobial Activity of Five Essential Oils against Bacteria and Fungi Responsible for Urinary Tract Infections
by Valentina Virginia Ebani, Simona Nardoni, Fabrizio Bertelloni, Luisa Pistelli and Francesca Mancianti
Molecules 2018, 23(7), 1668; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules23071668 - 09 Jul 2018
Cited by 49 | Viewed by 8790
Abstract
Urinary tract infections are frequently encountered in small animal practice. Escherichia coli and Enterococcus spp. are the most common agents associated to these infections, even though other bacteria and yeasts, such as Candida albicans and Candida famata, may be involved. In view of [...] Read more.
Urinary tract infections are frequently encountered in small animal practice. Escherichia coli and Enterococcus spp. are the most common agents associated to these infections, even though other bacteria and yeasts, such as Candida albicans and Candida famata, may be involved. In view of the increasing problem of the multi-drug resistance, the aim of this study was to investigate the antimicrobial activity of essential oils obtained from star anise (Illicium verum Hook.f.), basil (Ocimum basilicum L.), origanum (Origanum vulgare L.), clary sage (Salvia sclarea L.) and thymus (Thymus vulgaris L.) against multidrug-resistant strains of Escherichia coli, Enterococcus spp., Candida albicans and Candida famata previously isolated from dogs and cats with urinary tract infections. Enterococci were resistant to Illicium verum and Salvia sclarea, such as Candida to Salvia sclarea. Thymus vulgaris and Origanum vulgare essential oils showed the best activity against all the tested pathogens, so they could be proposed for the formulation of external and/or intravesical washes in small animals. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents)
13 pages, 416 KiB  
Article
Antifungal and Cytotoxic Activities of Sixty Commercially-Available Essential Oils
by Chelsea N. Powers, Jessica L. Osier, Robert L. McFeeters, Carolyn Brianne Brazell, Emily L. Olsen, Debra M. Moriarity, Prabodh Satyal and William N. Setzer
Molecules 2018, 23(7), 1549; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules23071549 - 27 Jun 2018
Cited by 65 | Viewed by 8370
Abstract
There is an urgent and unmet need for new antifungal therapies. Global fungal infection rates continue to rise and fungal infections pose increasing burdens on global healthcare systems. Exacerbating the situation, the available antifungal therapeutic arsenal is limited and development of new antifungals [...] Read more.
There is an urgent and unmet need for new antifungal therapies. Global fungal infection rates continue to rise and fungal infections pose increasing burdens on global healthcare systems. Exacerbating the situation, the available antifungal therapeutic arsenal is limited and development of new antifungals has been slow. Current antifungals are known for unwanted side effects including nephrotoxicity and hepatotoxicity. Thus, the need for new antifungals and new antifungal targets is urgent and growing. A collection of 60 commercially-available essential oils has been screened for antifungal activity against Aspergillus niger, Candida albicans, and Cryptococcus neoformans, as well as for cytotoxic activity against MCF-7 and MDA-MB-231 human breast tumor cell lines; the chemical compositions of the essential oils have been determined by gas chromatography-mass spectrometry (GC-MS). Ten essential oils showed remarkable antifungal and cytotoxic activities: Indian, Australian, and Hawaiian sandalwoods; melissa; lemongrass; cilantro; cassia; cinnamon; patchouli; and vetiver. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents)
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13 pages, 289 KiB  
Article
Antibacterial Activity of Emulsified Pomelo (Citrus grandis Osbeck) Peel Oil and Water-Soluble Chitosan on Staphylococcus aureus and Escherichia coli
by Guan-Wen Chen, Yu-Hsin Lin, Chia-Hua Lin and Hsiao-Chin Jen
Molecules 2018, 23(4), 840; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules23040840 - 06 Apr 2018
Cited by 19 | Viewed by 6653
Abstract
This study utilized pomelo steam distillation to isolate pomelo peel essential oil. The constituents were then analyzed through gas chromatography-mass spectrometry (GC-MS), and the antibacterial activity of the essential oil emulsions at different homogenizer speed conditions and concentrations of water-soluble chitosan (degree of [...] Read more.
This study utilized pomelo steam distillation to isolate pomelo peel essential oil. The constituents were then analyzed through gas chromatography-mass spectrometry (GC-MS), and the antibacterial activity of the essential oil emulsions at different homogenizer speed conditions and concentrations of water-soluble chitosan (degree of acetylation, DA = 54.8%) against S. aureus and E. coli was examined. Analysis of the essential oil composition identified a total of 33 compounds with the main constituent, limonene accounting for 87.5% (940.07 mg/g) of the total. The pomelo peel oil was emulsified through homogenization at 24,000 rpm, resulting in a minimal inhibitory concentration (MIC) for E. coli that was 1.9 times lower than that of the essential oil without homogenization. In addition, a mixture of 0.4% essential oil emulsion and 0.03% water-soluble chitosan had the strongest synergetic antibacterial effect on S. aureus and E. coli at pH 7.4. In comparison with chitosan alone, the MIC value of this mixture was significantly 2.4 and 2.5 times lower. Hence, this study suggests using a mixture of emulsified pomelo peel oil and water-soluble chitosan to develop a novel natural food preservative, and that the processability of food, as well as the economic value of the byproducts of the Taiwan Matou pomelo and chitosan, could be increased. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents)
13 pages, 1333 KiB  
Article
Antimicrobial and Antibiofilm Activity and Machine Learning Classification Analysis of Essential Oils from Different Mediterranean Plants against Pseudomonas aeruginosa
by Marco Artini, Alexandros Patsilinakos, Rosanna Papa, Mijat Božović, Manuela Sabatino, Stefania Garzoli, Gianluca Vrenna, Marco Tilotta, Federico Pepi, Rino Ragno and Laura Selan
Molecules 2018, 23(2), 482; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules23020482 - 23 Feb 2018
Cited by 60 | Viewed by 7663
Abstract
Pseudomonas aeruginosa is a ubiquitous organism and opportunistic pathogen that can cause persistent infections due to its peculiar antibiotic resistance mechanisms and to its ability to adhere and form biofilm. The interest in the development of new approaches for the prevention and treatment [...] Read more.
Pseudomonas aeruginosa is a ubiquitous organism and opportunistic pathogen that can cause persistent infections due to its peculiar antibiotic resistance mechanisms and to its ability to adhere and form biofilm. The interest in the development of new approaches for the prevention and treatment of biofilm formation has recently increased. The aim of this study was to seek new non-biocidal agents able to inhibit biofilm formation, in order to counteract virulence rather than bacterial growth and avoid the selection of escape mutants. Herein, different essential oils extracted from Mediterranean plants were analyzed for their activity against P. aeruginosa. Results show that they were able to destabilize biofilm at very low concentration without impairing bacterial viability. Since the action is not related to a bacteriostatic/bactericidal activity on P. aeruginosa, the biofilm change of growth in presence of the essential oils was possibly due to a modulation of the phenotype. To this aim, application of machine learning algorithms led to the development of quantitative activity–composition relationships classification models that allowed to direct point out those essential oil chemical components more involved in the inhibition of biofilm production. The action of selected essential oils on sessile phenotype make them particularly interesting for possible applications such as prevention of bacterial contamination in the community and in healthcare environments in order to prevent human infections. We assayed 89 samples of different essential oils as P. aeruginosa anti-biofilm. Many samples inhibited P. aeruginosa biofilm at concentrations as low as 48.8 µg/mL. Classification of the models was developed through machine learning algorithms. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents)
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9 pages, 222 KiB  
Article
Activity of Salvia dolomitica and Salvia somalensis Essential Oils against Bacteria, Molds and Yeasts
by Valentina Virginia Ebani, Simona Nardoni, Fabrizio Bertelloni, Silvia Giovanelli, Barbara Ruffoni, Carlo D’Ascenzi, Luisa Pistelli and Francesca Mancianti
Molecules 2018, 23(2), 396; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules23020396 - 13 Feb 2018
Cited by 17 | Viewed by 4465
Abstract
Essential oils (EOs) from Salvia dolomitica and Salvia somalensis, widely employed in the cosmetic and perfume industry, were analyzed for composition and tested against bacterial and fungal pathogens isolated from clinical and environmental specimens. The analyses were carried out against Staphylococcus aureus [...] Read more.
Essential oils (EOs) from Salvia dolomitica and Salvia somalensis, widely employed in the cosmetic and perfume industry, were analyzed for composition and tested against bacterial and fungal pathogens isolated from clinical and environmental specimens. The analyses were carried out against Staphylococcus aureus, Staphylococcus pseudointermedius, Pseudomonas aeruginosa, Escherichia coli, Streptococcus canis, Streptococcus pyogenes, Klebsiella pneumoniae, Proteus mirabilis, Microsporum canis, Microsporum gypseum, Trichophyton mentagrophytes, Aspergillus niger, Aspergillus flavus, Candida albicans, Candida krusei, Mucor sp. and Trichothecium roseum. Both EOs showed similar percentages of total monoterpenes and sesquiterpene hydrocarbons. The main constituents were 1,8-cineole and β-caryophyllene in S. dolomitica and bornyl acetate and camphor in S. somalensis. The selected EOs have no relevant antifungal or antibacterial activities if compared to conventional drugs. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents)
10 pages, 625 KiB  
Article
Chemical Composition, Antimicrobial and Antioxidant Activities of the Flower Volatile Oils of Fagopyrum esculentum, Fagopyrum tataricum and Fagopyrum Cymosum
by Jianglin Zhao, Lan Jiang, Xiaohui Tang, Lianxin Peng, Xing Li, Gang Zhao and Lingyun Zhong
Molecules 2018, 23(1), 182; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules23010182 - 22 Jan 2018
Cited by 33 | Viewed by 6076
Abstract
The purpose of this study was to investigate the chemical composition and biological activity of the volatile oils (VOs) from the flowers of three buckwheat species, Fagopyrum esculentum, Fagopyrum tataricum and Fagopyrum cymosum. The VOs were obtained from the fresh buckwheat [...] Read more.
The purpose of this study was to investigate the chemical composition and biological activity of the volatile oils (VOs) from the flowers of three buckwheat species, Fagopyrum esculentum, Fagopyrum tataricum and Fagopyrum cymosum. The VOs were obtained from the fresh buckwheat flowers by hydrodistillation, and were analyzed for their chemical composition by gas chromatography-mass spectrometry (GC-MS). Nonanoic acid (7.58%), (E)-3-hexen-1-ol (6.52%), and benzothiazole (5.08%) were the major constituents among the 28 identified components which accounted for 92.89% of the total oil of F. esculentum. 2-Pentadecanone (18.61%), eugenol (17.18%), 1,2-benzenedicarboxylic acid, bis(2-methylpropyl) ester (13.19%), and (E,E)-farnesylacetone (7.15%) were the major compounds among the 14 identified components which accounted for 88.48% of the total oil of F. tataricum. Eugenol (12.22%), (E)-3-hexen-1-yl acetate (8.03%), linalool oxide (7.47%), 1-hexanol (7.07%), and benzothiazole (6.72%) were the main compounds of the 20 identified components which accounted for 90.23% of the total oil of F. cymosum. The three VOs were screened to have broad spectrum antibacterial activity with minimum inhibitory concentration (MIC) values ranged from 100.0 μg/mL to 800.0 μg/mL against the tested bacteria, and their median inhibitory concentration (IC50) values were from 68.32 μg/mL to 452.32 μg/mL. Xanthomonas vesicatoria was the most sensitive bacterium. Moreover, the flower VOs of F. esculentum, F. tataricum and F. cymosum also exhibited noteworthy antioxidant capacity with the IC50 value of 354.15 μg/mL, 210.63 μg/mL, and 264.92 μg/mL for the 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging assay, and the value of 242.06 μg/mL, 184.13 μg/mL, and 206.11 μg/mL respectively for the β-carotene-linoleic bleaching test. These results suggested the volatile oils of buckwheat flowers could be potential resource of natural antimicrobial and antioxidant agents. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents)
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15 pages, 1517 KiB  
Article
Synergistic Antifungal, Allelopatic and Anti-Proliferative Potential of Salvia officinalis L., and Thymus vulgaris L. Essential Oils
by Ersilia Alexa, Renata Maria Sumalan, Corina Danciu, Diana Obistioiu, Monica Negrea, Mariana-Atena Poiana, Cristian Rus, Isidora Radulov, Georgeta Pop and Cristina Dehelean
Molecules 2018, 23(1), 185; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules23010185 - 16 Jan 2018
Cited by 51 | Viewed by 6756
Abstract
The current study aimed to investigate the chemical composition and the synergistic potential of two essential oils (EOs), as obtained from Salvia officinalis L. (SEO), and Thymus vulgaris L. (TEO). The antifungal potential was tested in vitro against Fusarium graminearum (Fg 06_17), the [...] Read more.
The current study aimed to investigate the chemical composition and the synergistic potential of two essential oils (EOs), as obtained from Salvia officinalis L. (SEO), and Thymus vulgaris L. (TEO). The antifungal potential was tested in vitro against Fusarium graminearum (Fg 06_17), the herbicidal effect was studied using weed seeds of Amaranthus retroflexus (ARET), Chenopodium album (CALB), Echinochloa crus-galli (EGAL), but also wheat seeds (WS) of the Lovrin variety and tomato seeds Saint-Pierre of the variety. The GC-MS profile highlights that the mains compounds identified in SEO were: caryophyllene (25.364%), camphene (14.139%), eucalyptol (13.902%), and β-pinene (11.230%), while in TEO, the predominant phytochemicals were: γ-terpinene (68.415%) and p-thymol (24.721%). The results indicated that the tested EOs alone as well as in combination have allelopathic effect against investigated seeds, while the synergistic effect of TEO and SEO in terms of fungal growth was demonstrated at a level of 0.06%. Thyme and sage EOs exhibited in vitro anti-proliferative activity on two melanoma cell lines, namely A375 human melanoma and B164A5 mouse melanoma alone, as well as in combination. SEO was most effective in terms of decreasing the cell viability of murine and human melanoma cell lines when compared to TEO. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents)
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14 pages, 276 KiB  
Article
The Effect of Combining Natural Terpenes and Antituberculous Agents against Reference and Clinical Mycobacterium tuberculosis Strains
by Elwira Sieniawska, Rafal Sawicki, Marta Swatko-Ossor, Agnieszka Napiorkowska, Agata Przekora, Grazyna Ginalska, Marta Swatko-Ossor and Ewa Augustynowicz-Kopec
Molecules 2018, 23(1), 176; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules23010176 - 15 Jan 2018
Cited by 35 | Viewed by 4503
Abstract
Background: On account of emergence of multi- and extensively drug-resistant Mycobacterium tuberculosis (Mtb) strains, combinations of drugs with natural compounds were tested to search for antibiotic activity enhancers. In this work we studied terpenes (α-pinene, bisabolol, β-elemene, (R)-limonene, (S [...] Read more.
Background: On account of emergence of multi- and extensively drug-resistant Mycobacterium tuberculosis (Mtb) strains, combinations of drugs with natural compounds were tested to search for antibiotic activity enhancers. In this work we studied terpenes (α-pinene, bisabolol, β-elemene, (R)-limonene, (S)-limonene, myrcene, sabinene), which are the main constituents of essential oil obtained from Mutellina purpurea L., a plant with described antitubercular activity, to investigate their interactions with antibiotics against reference Mtb strains and multidrug-resistant clinical isolates. Methods: The serial dilution method was used to evaluate the minimal inhibitory concentration (MIC) of tested compounds, while the fractional inhibitory concentration index (FICI) was calculated for characterization of interactions. Moreover, IC50 values of tested compounds were determined using monkey kidney epithelial cell line (GMK). Results: The combinations of all studied terpenes with ethambutol or rifampicin resulted in a synergistic interaction. Bisabolol and (R)-limonene decreased the MIC for rifampicin at least two-fold for all tested strains, however no synergistic action was observed against virulent strains. The tested terpenes showed slight (bisabolol) or no cytotoxic effect against normal eukaryotic cells in vitro. Conclusions: The obtained enhanced activity (FICI < 0.5) of ethambutol and rifampicin against H37Ra strain under the influence of the studied terpenes may be correlated to the capability of essential oil constituents to modify bacterial resistance mechanisms in general. The observed differences in avirulent and virulent bacteria susceptibility to terpenes tested separately and in combinations with antibiotics can be correlated with the differences in the cell wall structure between H37Ra mutant and all virulent strains. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents)
3313 KiB  
Article
Calli Essential Oils Synergize with Lawsone against Multidrug Resistant Pathogens
by Sameh S. M. Soliman, Abrar I. Alsaadi, Eman G. Youssef, Gregory Khitrov, Ayman M. Noreddin, Mohamed I. Husseiny and Ashraf S. Ibrahim
Molecules 2017, 22(12), 2223; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules22122223 - 20 Dec 2017
Cited by 34 | Viewed by 5630
Abstract
The fast development of multi-drug resistant (MDR) organisms increasingly threatens global health and well-being. Plant natural products have been known for centuries as alternative medicines that can possess pharmacological characteristics, including antimicrobial activities. The antimicrobial activities of essential oil (Calli oil) extracted from [...] Read more.
The fast development of multi-drug resistant (MDR) organisms increasingly threatens global health and well-being. Plant natural products have been known for centuries as alternative medicines that can possess pharmacological characteristics, including antimicrobial activities. The antimicrobial activities of essential oil (Calli oil) extracted from the Calligonum comosum plant by hydro-steam distillation was tested either alone or when combined with lawsone, a henna plant naphthoquinone, against MDR microbes. Lawsone showed significant antimicrobial activities against MDR pathogens in the range of 200–300 µg/mL. Furthermore, Calli oil showed significant antimicrobial activities against MDR bacteria in the range of 180–200 µg/mL, Candida at 220–240 µg/mL and spore-forming Rhizopus fungus at 250 µg/mL. Calli oil’s inhibition effect on Rhizopus, the major cause of the lethal infection mucormycosis, stands for 72 h, followed by an extended irreversible white sporulation effect. The combination of Calli oil with lawsone enhanced the antimicrobial activities of each individual alone by at least three-fold, while incorporation of both natural products in a liposome reduced their toxicity by four- to eight-fold, while maintaining the augmented efficacy of the combination treatment. We map the antimicrobial activity of Calli oil to its major component, a benzaldehyde derivative. The findings from this study demonstrate that formulations containing essential oils have the potential in the future to overcome antimicrobial resistance. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents)
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2403 KiB  
Article
Anti-Candida Activity of Bursera morelensis Ramirez Essential Oil and Two Compounds, α-Pinene and γ-Terpinene—An In Vitro Study
by C. Rebeca Rivera-Yañez, L. Ignacio Terrazas, Manuel Jimenez-Estrada, Jorge E. Campos, Cesar M. Flores-Ortiz, Luis B. Hernandez, Tonatiuh Cruz-Sanchez, German I. Garrido-Fariña, Marco A. Rodriguez-Monroy and M. Margarita Canales-Martinez
Molecules 2017, 22(12), 2095; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules22122095 - 05 Dec 2017
Cited by 35 | Viewed by 5458
Abstract
The candidiasis caused by C. albicans is a public health problem. The abuse of antifungals has contributed to the development of resistance. B. morelensis has demonstrated antibacterial and antifungal activities. In this work the activity of the essential oil of B. morelensis was [...] Read more.
The candidiasis caused by C. albicans is a public health problem. The abuse of antifungals has contributed to the development of resistance. B. morelensis has demonstrated antibacterial and antifungal activities. In this work the activity of the essential oil of B. morelensis was evaluated and for its two pure compounds with analysis of the different mechanisms of pathogenesis important for C. albicans. The essential oil was obtained by the hydro-distillation method and analyzed using GC–MS. The anti-Candida activity was compared between to essential oil, α-Pinene and γ-Terpinene. GC–MS of the essential oil demonstrated the presence of 13 compounds. The essential oil showed antifungal activity against four C. albicans strains. The most sensitive strain was C. albicans 14065 (MFC 2.0 mg/mL and MIC50 0.125 mg/mL) with α-Pinene and γ-Terpinene having MFCs of 4.0 and 16.0 mg/mL respectively. The essential oil inhibited the growth of the germ tube in 87.94% (8.0 mg/mL). Furthermore, it was observed that the essential oil diminishes the transcription of the gene INT1. This work provides evidence that confirms the anti-Candida activity of the B. morelensis essential oil and its effect on the growth of the germ tube and transcription of the gene INT1. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents)
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402 KiB  
Article
Chemical Composition, Antibacterial Activity, and Synergistic Effects with Conventional Antibiotics and Nitric Oxide Production Inhibitory Activity of Essential Oil from Geophila repens (L.) I.M. Johnst
by Huijuanzi Rao, Pengxiang Lai and Yang Gao
Molecules 2017, 22(9), 1561; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules22091561 - 17 Sep 2017
Cited by 23 | Viewed by 5574
Abstract
Geophila repens (L.) I.M. Johnst, a perennial herb, belongs to the Rubiaceae family. In this study, we identified the chemical composition of the Geophila repens essential oil (GR-EO) for the first time. Totally, seventy-seven compounds were identified according to GC and GC-MS, which [...] Read more.
Geophila repens (L.) I.M. Johnst, a perennial herb, belongs to the Rubiaceae family. In this study, we identified the chemical composition of the Geophila repens essential oil (GR-EO) for the first time. Totally, seventy-seven compounds were identified according to GC and GC-MS, which represent 98.0% of the oil. And the major components of GR-EO were β-caryophyllene (23.3%), β-elemene (8.0%), farnesyl butanoate (7.4%), myrcene (3.5%), and trans-nerolidol (3.3%). Then we evaluated the antibacterial activities of GR-EO and the synergistic effects of GR-EO in combination with commercial antibiotics using the microdilution and Checkerboard method. The results demonstrated that GR-EO possessed an excellent broad spectrum antibacterial activity, especially against Pseudomonas aeruginosa and Bacillus subtilis. It also showed that the combined application of GR-EO with antibiotics led to synergistic effects in most cases. And the most prominent synergistic effect was noticed when GR-EO was in combination with Streptomycin and tested against Escherichia coli (fractional inhibitory concentration indices (FICI) of 0.13). Additionally, the results of a Griess assay revealed that GR-EO exhibited a potent inhibitory effect on NO production in lipopolysaccharide (LPS)-activated RAW 264.7 (murine macrophage) cells. In conclusion, the combination of GR-EO and the commercial antibiotics has significant potential for the development of new antimicrobial treatment and reduction of drug resistance. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents)
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2380 KiB  
Communication
In Vitro Evaluation of Sub-Lethal Concentrations of Plant-Derived Antifungal Compounds on FUSARIA Growth and Mycotoxin Production
by Caterina Morcia, Giorgio Tumino, Roberta Ghizzoni, Assetou Bara, Nesrine Salhi and Valeria Terzi
Molecules 2017, 22(8), 1271; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules22081271 - 29 Jul 2017
Cited by 27 | Viewed by 4701
Abstract
Phytopathogenic fungi can lead to significant cereal yield losses, also producing mycotoxins dangerous for human and animal health. The fungal control based on the use of synthetic fungicides can be complemented by "green" methods for crop protection, based on the use of natural [...] Read more.
Phytopathogenic fungi can lead to significant cereal yield losses, also producing mycotoxins dangerous for human and animal health. The fungal control based on the use of synthetic fungicides can be complemented by "green" methods for crop protection, based on the use of natural products. In this frame, the antifungal activities of bergamot and lemon essential oils and of five natural compounds recurrent in essential oils (citronellal, citral, cinnamaldehyde, cuminaldehyde and limonene) have been evaluated against three species of mycotoxigenic fungi (Fusarium sporotrichioides, F. graminearum and F. langsethiae) responsible for Fusarium Head Blight in small-grain cereals. The natural products concentrations effective for reducing or inhibiting the in vitro fungal growth were determined for each fungal species and the following scale of potency was found: cinnamaldehyde > cuminaldehyde > citral > citronellal > bergamot oil > limonene > lemon oil. Moreover, the in vitro mycotoxin productions of the three Fusaria strains exposed to sub-lethal concentrations of the seven products was evaluated. The three fungal species showed variability in response to the treatments, both in terms of inhibition of mycelial growth and in terms of modulation of mycotoxin production that can be enhanced by sub-lethal concentrations of some natural products. This last finding must be taken into account in the frame of an open field application of some plant-derived fungicides. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents)
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971 KiB  
Article
Cardamom, Cumin, and Dill Weed Essential Oils: Chemical Compositions, Antimicrobial Activities, and Mechanisms of Action against Campylobacter spp.
by Aysegul Mutlu-Ingok and Funda Karbancioglu-Guler
Molecules 2017, 22(7), 1191; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules22071191 - 15 Jul 2017
Cited by 63 | Viewed by 8030
Abstract
Natural antimicrobials as well as essential oils (EOs) have gained interest to inhibit pathogenic microorganisms and to control food borne diseases. Campylobacter spp. are one of the most common causative agents of gastroenteritis. In this study, cardamom, cumin, and dill weed EOs were [...] Read more.
Natural antimicrobials as well as essential oils (EOs) have gained interest to inhibit pathogenic microorganisms and to control food borne diseases. Campylobacter spp. are one of the most common causative agents of gastroenteritis. In this study, cardamom, cumin, and dill weed EOs were evaluated for their antibacterial activities against Campylobacter jejuni and Campylobacter coli by using agar-well diffusion and broth microdilution methods, along with the mechanisms of antimicrobial action. Chemical compositions of EOs were also tested by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). The results showed that cardamom and dill weed EOs possess greater antimicrobial activity than cumin with larger inhibition zones and lower minimum inhibitory concentrations. The permeability of cell membrane and cell membrane integrity were evaluated by determining relative electric conductivity and release of cell constituents into supernatant at 260 nm, respectively. Moreover, effect of EOs on the cell membrane of Campylobacter spp. was also investigated by measuring extracellular ATP concentration. Increase of relative electric conductivity, extracellular ATP concentration, and cell constituents’ release after treatment with EOs demonstrated that tested EOs affected the membrane integrity of Campylobacter spp. The results supported high efficiency of cardamom, cumin, and dill weed EOs to inhibit Campylobacter spp. by impairing the bacterial cell membrane. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents)
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Review

Jump to: Research

21 pages, 308 KiB  
Review
Antimicrobial Activity and Chemical Composition of Essential Oils from Verbenaceae Species Growing in South America
by Cristina M. Pérez Zamora, Carola A. Torres and María B. Nuñez
Molecules 2018, 23(3), 544; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules23030544 - 01 Mar 2018
Cited by 49 | Viewed by 7166
Abstract
The Verbenaceae family includes 2600 species grouped into 100 genera with a pantropical distribution. Many of them are important elements of the floras of warm-temperature and tropical regions of America. This family is known in folk medicine, and its species are used as [...] Read more.
The Verbenaceae family includes 2600 species grouped into 100 genera with a pantropical distribution. Many of them are important elements of the floras of warm-temperature and tropical regions of America. This family is known in folk medicine, and its species are used as digestive, carminative, antipyretic, antitussive, antiseptic, and healing agents. This review aims to collect information about the essential oils from the most reported species of the Verbenaceae family growing in South America, focusing on their chemical composition, antimicrobial activity, and synergism with commercial antimicrobials. The information gathered comprises the last twenty years of research within the South American region and is summarized taking into consideration the most representative species in terms of their essential oils. These species belong to Aloysia, Lantana, Lippia, Phyla, and Stachytarpheta genera, and the main essential oils they contain are monoterpenes and sesquiterpenes, such as β-caryophyllene, thymol, citral, 1,8-cineole, carvone, and limonene. These compounds have been found to possess antimicrobial activities. The synergism of these essential oils with antibiotics is being studied by several research groups. It constitutes a resource of interest for the potential use of combinations of essential oils and antibiotics in infection treatments. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents)
477 KiB  
Review
Plants of the Genus Zingiber as a Source of Bioactive Phytochemicals: From Tradition to Pharmacy
by Mehdi Sharifi-Rad, Elena Maria Varoni, Bahare Salehi, Javad Sharifi-Rad, Karl R. Matthews, Seyed Abdulmajid Ayatollahi, Farzad Kobarfard, Salam A. Ibrahim, Dima Mnayer, Zainul Amiruddin Zakaria, Majid Sharifi-Rad, Zubaida Yousaf, Marcello Iriti, Adriana Basile and Daniela Rigano
Molecules 2017, 22(12), 2145; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules22122145 - 04 Dec 2017
Cited by 207 | Viewed by 16854
Abstract
Plants of the genus Zingiber (Family Zingiberaceae) are widely used throughout the world as food and medicinal plants. They represent very popular herbal remedies in various traditional healing systems; in particular, rhizome of Zingiber spp. plants has a long history of ethnobotanical uses [...] Read more.
Plants of the genus Zingiber (Family Zingiberaceae) are widely used throughout the world as food and medicinal plants. They represent very popular herbal remedies in various traditional healing systems; in particular, rhizome of Zingiber spp. plants has a long history of ethnobotanical uses because of a plethora of curative properties. Antimicrobial activity of rhizome essential oil has been extensively confirmed in vitro and attributed to its chemical components, mainly consisting of monoterpene and sesquiterpene hydrocarbons such as α-zingiberene, ar-curcumene, β-bisabolene and β-sesquiphellandrene. In addition, gingerols have been identified as the major active components in the fresh rhizome, whereas shogaols, dehydrated gingerol derivatives, are the predominant pungent constituents in dried rhizome. Zingiber spp. may thus represent a promising and innovative source of natural alternatives to chemical food preservatives. This approach would meet the increasing concern of consumers aware of the potential health risks associated with the conventional antimicrobial agents in food. This narrative review aims at providing a literature overview on Zingiber spp. plants, their cultivation, traditional uses, phytochemical constituents and biological activities. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents)
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