molecules-logo

Journal Browser

Journal Browser

Special Issue "Essential Oils as Antimicrobial and Anti-infectious Agents II"

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

Deadline for manuscript submissions: 15 December 2020.

Special Issue Editor

Prof. Dr. Daniela Rigano
Website1 Website2
Guest Editor
Department of Pharmacy, School of Medicine and Surgery, University Federico II of Naples, Via Domenico Montesano, 49, Naples 80131, Italy
Interests: natural products; structure elucidation; essential oils; NMR spectroscopy; GC-MS and LC-MS
Special Issues and Collections in MDPI journals

Special Issue Information

Dear Colleagues,

In the last decades, infectious diseases have continued to be a major health concern worldwide, causing important epidemiological, financial, and logistical implications. Essential oils (EOs) are considered an important source for new natural antimicrobials, particularly for multidrug-resistant bacteria, pathogenic fungi, viruses, and parasites. 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, following the success of the first issue in 2018, aims to attract contributions on all aspects of the chemistry and antimicrobial activity of essential oils. Original research articles and reviews that make substantial advances within this field are invited to contribute to this editorial project.

Prof. Daniela Rigano
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Essential oils
  • Antimicrobials
  • Bacterial infections
  • Fungi
  • Viruses
  • Parasites
  • Resistance

Published Papers (12 papers)

Order results
Result details
Select all
Export citation of selected articles as:

Research

Jump to: Review

Open AccessArticle
Antimicrobial Activity of Different Artemisia Essential Oil Formulations
Molecules 2020, 25(10), 2390; https://doi.org/10.3390/molecules25102390 - 21 May 2020
Abstract
The extreme lipophilicity of essential oils (EOs) impedes the measurement of their biological actions in an aqueous environment. We formulated oil in water type Pickering Artemisia annua EO nanoemulsions (AEP) with surface-modified Stöber silica nanoparticles (20 nm) as the stabilizing agent. The antimicrobial [...] Read more.
The extreme lipophilicity of essential oils (EOs) impedes the measurement of their biological actions in an aqueous environment. We formulated oil in water type Pickering Artemisia annua EO nanoemulsions (AEP) with surface-modified Stöber silica nanoparticles (20 nm) as the stabilizing agent. The antimicrobial activity of AEP and its effects on mature Candida biofilms were compared with those of Tween 80 stabilized emulsion (AET) and ethanolic solution (AEE) of the Artemisia EO. The antimicrobial activity was evaluated by using the minimum inhibitory concentrations (MIC90) and minimum effective concentrations (MEC10) of the compounds. On planktonic bacterial and fungal cells beside growth inhibition, colony formation (CFU/mL), metabolic activity, viability, intracellular ATP/total protein (ATP/TP), along with reactive oxygen species (ROS) were also studied. Artemisia annua EO nanoemulsion (AEP) showed significantly higher antimicrobial activity than AET and AEE. Artemisia annua EO nanoemulsions (AEP) generated superoxide anion and peroxides-related oxidative stress, which might be the underlying mode of action of the Artemisia EO. Unilamellar liposomes, as a cellular model, were used to examine the delivery efficacy of the EO of our tested formulations. We could demonstrate higher effectiveness of AEP in the EO components’ donation compared to AET and AEE. Our data suggest the superiority of the AEP formulation against microbial infections. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents II)
Show Figures

Figure 1

Open AccessArticle
Comparative Evaluation of Essential Oils from Medicinal-Aromatic Plants of Greece: Chemical Composition, Antioxidant Capacity and Antimicrobial Activity against Bacterial Fish Pathogens
Molecules 2020, 25(1), 148; https://doi.org/10.3390/molecules25010148 - 30 Dec 2019
Abstract
The administration of antibiotics in aquaculture has raised concern about the impact of their overuse in marine ecosystems, seafood safety and consumers’ health. This “green consumerism” has forced researchers to find new alternatives against fish pathogens. The present study focused on 12 Mediterranean [...] Read more.
The administration of antibiotics in aquaculture has raised concern about the impact of their overuse in marine ecosystems, seafood safety and consumers’ health. This “green consumerism” has forced researchers to find new alternatives against fish pathogens. The present study focused on 12 Mediterranean medicinal-aromatic plants as potential antimicrobials and antioxidant agents that could be used in fish aquaculture. In vitro assays showed that the essential oils (EOs) from all studied plants had anti-bacterial and antioxidant properties, with their efficacy being dependent on their chemical composition. More specifically, EOs rich in carvacrol, p-cymene and γ-terpinene exhibited not only the strongest inhibitory activity against the growth of bacterial pathogens (inhibitory concentration: 26–88 μg mL−1), but also the greatest total antioxidant capacity (ABTS: 2591–5879 μmole mL−1; CUPRAC: 931–2733 μmole mL−1). These compounds were mainly found in the EOs from Greek oregano (Origanum vulgare subsp. hirtum), Spanish oregano (Thymbra capitata) and savoury (Satureja thymbra) collected from cultivations in Greece. The specific EOs stand out as promising candidates for the treatment of bacterial diseases and oxidative stress in farmed fish. Further in vivo experiments are needed to fully understand the effects of EO dietary supplementation on fish farming processes. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents II)
Show Figures

Figure 1

Open AccessArticle
The Effect of Ten Essential Oils on Several Cutaneous Drug-Resistant Microorganisms and Their Cyto/Genotoxic and Antioxidant Properties
Molecules 2019, 24(24), 4570; https://doi.org/10.3390/molecules24244570 - 13 Dec 2019
Cited by 1
Abstract
In this study, we determined the antimicrobial activity of ten essential oils (EOs)—oregano, thyme, clove, arborvitae, cassia, lemongrass, melaleuca, eucalyptus, lavender, and clary sage—against drug-resistant microorganisms previously isolated from patients with skin infections. The essential oil compositions were determined using gas chromatography coupled [...] Read more.
In this study, we determined the antimicrobial activity of ten essential oils (EOs)—oregano, thyme, clove, arborvitae, cassia, lemongrass, melaleuca, eucalyptus, lavender, and clary sage—against drug-resistant microorganisms previously isolated from patients with skin infections. The essential oil compositions were determined using gas chromatography coupled to mass spectrometry (GC/MS). The assayed bacteria included Pseudomonas aeruginosa, Proteus vulgaris, Citrobacter koseri, and Klebsiella pneumoniae. Two drug-resistant yeasts (Candida albicans and Candida parapsilosis) were also involved in our survey. Oregano, thyme, cassia, lemongrass and arborvitae showed very strong antibacterial and antifungal activity against all tested strains. These results show that these essential oils may be effective in preventing the growth of the drug-resistant microorganisms responsible for wound infections. In this study, the genotoxic effects of tested essential oils on healthy human keratinocytes HaCaT were evaluated using the comet assay for the first time. These results revealed that none of the essential oils induced significant DNA damage in vitro after 24 h. Moreover, the treatment of HaCaT cells with essential oils increased the total antioxidant status (TAS) level. The obtained results indicate that EOs could be used as a potential source of safe and potent natural antimicrobial and antioxidant agents in the pharmaceutical and food industries. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents II)
Show Figures

Figure 1

Open AccessFeature PaperArticle
Chemical Composition and Antimicrobial Activity of Artemisia herba-alba and Origanum majorana Essential Oils from Morocco
Molecules 2019, 24(22), 4021; https://doi.org/10.3390/molecules24224021 - 06 Nov 2019
Cited by 1
Abstract
Essential oils (EOs) are one of the most important groups of plant metabolites responsible for their biological activities. This study was carried out to study the chemical composition and the antimicrobial effects of Artemisia herba-alba and Origanum majorana essential oils against some Gram-positive [...] Read more.
Essential oils (EOs) are one of the most important groups of plant metabolites responsible for their biological activities. This study was carried out to study the chemical composition and the antimicrobial effects of Artemisia herba-alba and Origanum majorana essential oils against some Gram-positive and Gram-negative bacteria, and a fungal strain isolated from spoiled butter. The plants were collected in the region Azzemour of South West Morocco and the EOs, extracted by hydrodistillation, were analyzed by GC-MS. The antimicrobial activity was determined using the agar paper disc method. The main components of A. herba-alba EO were cis-thujone, trans-thujone and vanillyl alcohol; in O. majorana EO terpinen-4-ol, isopulegol and β-phellandrene predominated. Both essential oils exhibited growth inhibiting activities in a concentration-dependent manner on several microorganism species. Our results demonstrated that O. majorana and A. herba-alba EOs could be effective natural antibacterial agents in foods. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents II)
Show Figures

Figure 1

Open AccessArticle
Chemical Composition and Antimicrobial Effectiveness of Ocimum gratissimum L. Essential Oil Against Multidrug-Resistant Isolates of Staphylococcus aureus and Escherichia coli
Molecules 2019, 24(21), 3864; https://doi.org/10.3390/molecules24213864 - 26 Oct 2019
Cited by 1
Abstract
The study investigated the antimicrobial activity of the essential oil extract of Ocimum gratissimum L. (EOOG) against multiresistant microorganisms in planktonic and biofilm form. Hydrodistillation was used to obtain the EOOG, and the analysis of chemical composition was done by gas chromatography coupled [...] Read more.
The study investigated the antimicrobial activity of the essential oil extract of Ocimum gratissimum L. (EOOG) against multiresistant microorganisms in planktonic and biofilm form. Hydrodistillation was used to obtain the EOOG, and the analysis of chemical composition was done by gas chromatography coupled with mass spectrometry (GC/MS) and flame ionization detection (GC/FID). EOOG biological activity was verified against isolates of Staphylococcus aureus and Escherichia coli, using four strains for each species. The antibacterial action of EOOG was determined by disk diffusion, microdilution (MIC/MBC), growth curve under sub-MIC exposure, and the combinatorial activity with ciprofloxacin (CIP) and oxacillin (OXA) were determined by checkerboard assay. The EOOG antibiofilm action was performed against the established biofilm and analyzed by crystal violet, colony-forming unit count, and SEM analyses. EOOG yielded 1.66% w/w, with eugenol as the major component (74.83%). The MIC was 1000 µg/mL for the most tested strains. The growth curve showed a lag phase delay for both species, mainly S. aureus, and reduced the growth level of E. coli by half. The combination of EOOG with OXA and CIP led to an additive action for S. aureus. A significant reduction in biofilm biomass and cell viability was verified for S. aureus and E. coli. In conclusion, EOOG has relevant potential as a natural alternative to treat infections caused by multiresistant strains. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents II)
Show Figures

Graphical abstract

Open AccessArticle
Enhanced Killing of Candida krusei by Polymorphonuclear Leucocytes in the Presence of Subinhibitory Concentrations of Melaleuca alternifolia and “Mentha of Pancalieri” Essential Oils
Molecules 2019, 24(21), 3824; https://doi.org/10.3390/molecules24213824 - 23 Oct 2019
Abstract
The aim of this study was to evaluate the influence of tea tree oil (TTO) and “Mentha of Pancalieri” essential oil (MPP) on intracellular killing of Candida krusei, often resistant to conventional drugs, by polymorphonuclear leucocytes (PMNs). Intracellular killing was investigated by incubating [...] Read more.
The aim of this study was to evaluate the influence of tea tree oil (TTO) and “Mentha of Pancalieri” essential oil (MPP) on intracellular killing of Candida krusei, often resistant to conventional drugs, by polymorphonuclear leucocytes (PMNs). Intracellular killing was investigated by incubating yeasts and PMNs with essential oils (EOs) at 1/4 and 1/8 × MIC (Minimal Inhibitory Concentration), in comparison with anidulafungin, used as a reference drug. Killing values were expressed as Survival Index (SI) values. The cytotoxicity of EOs was evaluated by 3-[4,-5-dimethylthiazole-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay. Both EOs were more efficaceous at 1/8 × MIC than 1/4 × MIC, with killing values higher than observed in EO-free systems and in presence of anidulafungin, indicating that the decreasing concentrations did not cause lower candidacidal activity. This better activity at 1/8 × MIC is probably due to the EOs’ toxicity at 1/4 × MIC, suggesting that at higher concentrations EOs might interfere with PMNs functionality. TTO and MPP at 1/8 × MIC significantly increased intracellular killing by PMNs through their direct action on the yeasts (both EOs) or on phagocytic cells (MPP), suggesting a positive interaction between EOs and PMNs to eradicate intracellular C. krusei. These data showed a promising potential application of TTO and “Mentha of Pancalieri” EO as natural adjuvants in C. krusei infection management. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents II)
Show Figures

Graphical abstract

Open AccessArticle
Evaluation of the Antifungal Activity of Mentha x piperita (Lamiaceae) of Pancalieri (Turin, Italy) Essential Oil and Its Synergistic Interaction with Azoles
Molecules 2019, 24(17), 3148; https://doi.org/10.3390/molecules24173148 - 29 Aug 2019
Cited by 2
Abstract
The promising antimicrobial activity of essential oils (EOs) has led researchers to use them in combination with antimicrobial drugs in order to reduce drug toxicity, side effects, and resistance to single agents. Mentha x piperita, known worldwide as “Mentha of Pancalieri”, is [...] Read more.
The promising antimicrobial activity of essential oils (EOs) has led researchers to use them in combination with antimicrobial drugs in order to reduce drug toxicity, side effects, and resistance to single agents. Mentha x piperita, known worldwide as “Mentha of Pancalieri”, is produced locally at Pancalieri (Turin, Italy). The EO from this Mentha species is considered as one of the best mint EOs in the world. In our research, we assessed the antifungal activity of “Mentha of Pancalieri” EO, either alone or in combination with azole drugs (fluconazole, itraconazole, ketoconazole) against a wide panel of yeast and dermatophyte clinical isolates. The EO was analyzed by GC-MS, and its antifungal properties were evaluated by minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) parameters, in accordance with the CLSI guidelines, with some modifications. The interaction of EO with azoles was evaluated through the chequerboard and isobologram methods. The results suggest that this EO exerts a fungicidal activity against yeasts and a fungistatic activity against dermatophytes. Interaction studies with azoles indicated mainly synergistic profiles between itraconazole and EO vs. Candida spp., Cryptococcus neoformans, and Trichophyton mentagrophytes. Thus, the “Mentha of Pancalieri” EO may act as a potential antifungal agent and could serve as a natural adjuvant for fungal infection treatment. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents II)
Show Figures

Graphical abstract

Open AccessArticle
The Influence of Essential Oil Compounds on Antibacterial Activity of Mupirocin-Susceptible and Induced Low-Level Mupirocin-Resistant MRSA Strains
Molecules 2019, 24(17), 3105; https://doi.org/10.3390/molecules24173105 - 27 Aug 2019
Cited by 1
Abstract
Because of the bacterial drug resistance development, it is reasonable to investigate chemical compounds capable of preventing the spread of resistance to mupirocin (MUP), commonly used in staphylococcal eradication. The objective of the study was to verify the influence of essential oil compounds [...] Read more.
Because of the bacterial drug resistance development, it is reasonable to investigate chemical compounds capable of preventing the spread of resistance to mupirocin (MUP), commonly used in staphylococcal eradication. The objective of the study was to verify the influence of essential oil compounds (EOCs) on the antibacterial activity of MUP against mupirocin-susceptible (MupS) and induced low-level mupirocin-resistant (MupRL) methicillin-resistant Staphylococcus aureus (MRSA) strains. The following parameters were examined: MRSAMupS and MRSAMupRL susceptibility to EOCs (1,8-cineole, eugenol, carvacrol, linalool, (-)-menthone, linalyl acetate, and trans-anethole), the bacterial cell size distribution, and chemical composition by the use of Fourier Transform Infrared Spectroscopy (FTIR) and Raman spectroscopies. The MRSAMupS and MRSAMupRL strains were susceptible to all tested EOCs. 1,8-cineole and (-)-menthone showed synergistic activity against MRSAMupS in combination with mupirocin, whereas 1,8-cineole exhibited synergistic activity against MRSAMupRL as well. In-depth analysis showed that both MRSAMupS and MRSAMupRL displayed similar distributions of the bacterial cell size. The FTIR and Raman spectra of the MRSAMupS and MRSAMupRL strains showed differences in some regions. New bands in the MRSAMupRL Raman spectrum were observed. It was concluded that the use of 1,8-cineole in combination with mupirocin can increase the mupirocin activity against the MRSAMupS and MRSAMupRL strains. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents II)
Show Figures

Graphical abstract

Open AccessArticle
Analysis of Chemical Composition and Assessment of Cytotoxic, Antimicrobial, and Antioxidant Activities of the Essential Oil of Meriandra dianthera Growing in Saudi Arabia
Molecules 2019, 24(14), 2647; https://doi.org/10.3390/molecules24142647 - 22 Jul 2019
Cited by 3
Abstract
The essential oil of Meriandra dianthera (Konig ex Roxb.) Benth. (Synonym: Meriandra bengalensis, Lamiaceae) collected from Saudi Arabia was studied utilizing GC and GC/MS. Forty four constituents were identified, representing 96.8% of the total oil. The M. dianthera essential oil (MDEO) was [...] Read more.
The essential oil of Meriandra dianthera (Konig ex Roxb.) Benth. (Synonym: Meriandra bengalensis, Lamiaceae) collected from Saudi Arabia was studied utilizing GC and GC/MS. Forty four constituents were identified, representing 96.8% of the total oil. The M. dianthera essential oil (MDEO) was characterized by a high content of oxygenated monoterpenes (76.2%). Camphor (54.3%) was the major compound in MDEO followed by 1,8-cineole (12.2%) and camphene (10.4%). Moreover, MDEO was assessed for its cytotoxic, antimicrobial, and antioxidant activities. MDEO demonstrated an interesting cytotoxic activity against all cancer cell lines with IC50 values of 83.6 to 91.2 μg/mL, especially against MCF-7 cancer cells. Using labeling with annexin VFITC and/or propidium iodide (PI) dyes and flow cytometer analysis, the apoptosis induction was quantitatively confirmed for MCF-7 cells. The MDEO exhibited a considerable antimicrobial activity against all bacterial and fungal strains with minimum inhibitory concentration (MIC)-values of 0.07 to 1.25 mg/mL. The most sensitive microbial strain was Staphylococcus aureus (MIC: 0.07 mg/mL). Minimum bactericidal concentration (MBC) or minimum fungicidal concentration (MFC) values were determined one time higher than that of MIC’s. Additionally, the MDEO revealed a strong activity for reducing β-carotene bleaching with a total antioxidant value of 72.6% and significant DPPH free radical scavenging activity (78.4%) at the concentration 1000 μg/mL. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents II)
Show Figures

Figure 1

Open AccessArticle
Antimicrobial and Phytotoxic Activity of Origanum heracleoticum and O. majorana Essential Oils Growing in Cilento (Southern Italy)
Molecules 2019, 24(14), 2576; https://doi.org/10.3390/molecules24142576 - 16 Jul 2019
Cited by 8
Abstract
There is a growing interest in a potential use of essential oils (EOs) as a replacement for traditional pesticides and herbicides. The aims of this study were to: (i) Identify the chemical composition of the two EOs derived from Origanum heracleoticum L. and [...] Read more.
There is a growing interest in a potential use of essential oils (EOs) as a replacement for traditional pesticides and herbicides. The aims of this study were to: (i) Identify the chemical composition of the two EOs derived from Origanum heracleoticum L. and O. majorana L., (ii) evaluate the in vitro antifungal activity of the EOs against some postharvest phytopathogens (Botrytis cinerea, Penicillium expansum, Aspergillus niger and Monilinia fructicola), (iii) evaluate the in vitro antibacterial activity against Bacillus megaterium, Clavibacter michiganensis, Xanthomonas campestris, Pseudomonas fluorescens and P. syringae pv. phaseolicola, (iv) evaluate the effect of both studied EOs on the spore germination percentage and their minimum inhibitory concentration (MIC) against M. fructicola, and (v) study the possible phytotoxicity of the two EOs and their major constituents, carvacrol for O. heracleoticum and terpinen-4-ol for O. majorana, against tha germination and initial radicle growth of radish, lettuce, garden cress and tomato. The two EOs demonstrated promising in vitro antimicrobial and antifungal activities against all tested microorganisms. EOs showed high inhibition of spore germination percentage at the minimal inhibitory concentration of 500 and 2000 µg/mL, respectively. Moreover, both germination and radical elongation of selected plant species were sensitive to the oils. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents II)
Show Figures

Figure 1

Review

Jump to: Research

Open AccessReview
Recent Advances in the Application of Antibacterial Complexes Using Essential Oils
Molecules 2020, 25(7), 1752; https://doi.org/10.3390/molecules25071752 - 10 Apr 2020
Abstract
Although antibacterial spectrum of essential oils (EOs) has been analyzed along with consumers’ needs on natural biocides, singular treatments generally require high concentration of EOs and long-term exposures to eliminate target bacteria. To overcome these limitations, antibacterial complex has been developed and this [...] Read more.
Although antibacterial spectrum of essential oils (EOs) has been analyzed along with consumers’ needs on natural biocides, singular treatments generally require high concentration of EOs and long-term exposures to eliminate target bacteria. To overcome these limitations, antibacterial complex has been developed and this review analyzed previous reports regarding the combined antibacterial effects of EOs. Since unexpectable combined effects (synergism or antagonism) can be derived from the treatment of antibacterial complex, synergistic and antagonistic combinations have been identified to improve the treatment efficiency and to avoid the overestimation of bactericidal efficacy, respectively. Although antibacterial mechanism of EOs is not yet clearly revealed, mode of action regarding synergistic effects especially for the elimination of pathogens by using low quantity of EOs with short-term exposure was reported. Whereas comprehensive analysis on previous literatures for EO-based disinfectant products implies that the composition of constituents in antibacterial complexes is variable and thus analyzing the impact of constituting substances (e.g., surfactant, emulsifier) on antibacterial effects is further needed. This review provides practical information regarding advances in the EO-based combined treatment technologies and highlights the importance of following researches on the interaction of constituents in antibacterial complex to clarify the mechanisms of antibacterial synergism and/or antagonism. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents II)
Show Figures

Figure 1

Open AccessReview
Essential Oils and Mono/bi/tri-Metallic Nanocomposites as Alternative Sources of Antimicrobial Agents to Combat Multidrug-Resistant Pathogenic Microorganisms: An Overview
Molecules 2020, 25(5), 1058; https://doi.org/10.3390/molecules25051058 - 27 Feb 2020
Abstract
Over the past few decades, many pathogenic bacteria have become resistant to existing antibiotics, which has become a threat to infectious disease control worldwide. Hence, there has been an extensive search for new, efficient, and alternative sources of antimicrobial agents to combat multidrug-resistant [...] Read more.
Over the past few decades, many pathogenic bacteria have become resistant to existing antibiotics, which has become a threat to infectious disease control worldwide. Hence, there has been an extensive search for new, efficient, and alternative sources of antimicrobial agents to combat multidrug-resistant pathogenic microorganisms. Numerous studies have reported the potential of both essential oils and metal/metal oxide nanocomposites with broad spectra of bioactivities including antioxidant, anticancer, and antimicrobial attributes. However, only monometallic nanoparticles combined with essential oils have been reported on so far with limited data. Bi- and tri-metallic nanoparticles have attracted immense attention because of their diverse sizes, shapes, high surface-to-volume ratios, activities, physical and chemical stability, and greater degree of selectivity. Combination therapy is currently blooming and represents a potential area that requires greater attention and is worthy of future investigations. This review summarizes the synergistic effects of essential oils with other antimicrobial combinations such as mono-, bi-, and tri-metallic nanocomposites. Thus, the various aspects of this comprehensive review may prove useful in the development of new and alternative therapeutics against antibiotic resistant pathogens in the future. Full article
(This article belongs to the Special Issue Essential Oils as Antimicrobial and Anti-infectious Agents II)
Show Figures

Figure 1

Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Title: Evaluation of the antifungal activity of mentha of pancalieri (turin, italy) essential oil and synergistic interaction with azoles
Authors: Vivian Tullio et al.
Affiliation: Department of Public Health and Paediatrics, Microbiology Division, University of Turin, Turin, Italy
Abstract: With the wide use of synthetic and semi-synthetic antimicrobial drugs, pros and cons have been so far experienced, including the spread of drug resistant pathogens, and have directed research back to natural products as useful antimicrobial resources. Currently, there is evidence that essential oils (EOs) may exert remarkable biological activities against viruses, bacteria, fungi and parasites. The antimicrobial activity of Eos is due to a number of small terpenoids and phenol compounds. Several EOs are generally recognized as safe, do not accumulate in the liver or kidneys, can stimulate the immune system, and cause no resistance, since microbes are unable to adapt to their heterogeneous structure. The promising antimicrobial activity of Eos has led researchers to use them in combination with available antimicrobial drugs, in order to reduce drug toxicity and side effects, as well as to overcome drug resistance with single agents. Mentha x piperita L. (peppermint) EO is one of the most widely produced and consumed essential oils. Literature data have shown that peppermint EO and its main components (menthol and menthone) display antimicrobial properties, but their mechanism of action is still not clear. Near Torino, in Pancalieri, there is a typical local production of M.piperita [(Huds) species OFFICINALIS (Sole),RUBESCENS (Camus)kind], worldwide known as “Menta di Pancalieri”. This EO, thanks to its high quality, is actually considered by experts to be as one of the best peppermint EO in the world. In this study, we evaluated the antifungal activity of “Menta di Pancalieri” EO either alone or in combination with azole drugs against a wide panel of yeast and dermatophyte clinical isolates. The EO was analysed by GC-MS at Drug Science and Technology Dept., and its antifungal activity (MIC,MFC) was evaluated against 16 Candida spp.,15 non-Candida spp.,and 5 dermatophyte strains (Microsporum canis, M.gypseum, Trichophyton mentagrophytes) according to the CLSI guidelines, with some modifications. The interaction of peppermint EO with azole drugs (fluconazole, itraconazole, ketoconazole) was evaluated through the chequerboard and isobologram methods. The phytochemical composition of peppermint of Pancalieri EO was in agreement with the European Pharmacopoeia. Susceptibility test results suggest this EO exerts a fungicidal activity against yeasts, and a fungistatic activity against dermatophytes. Interaction studies with azole drugs indicate mainly synergistic profiles between itraconazole and peppermint EO vs. Candida spp., Cryptococcus neoformans and T.mentagrophytes. Peppermint of Pancalieri EO may act as a potential antifungal agent and may serve as a natural adjuvant for fungal infection treatment.

Title: Positive influence of tea tree oil on human PMN intracellular killing against Candida krusei
Authors: Vivian Tullio et al.
Affiliation: Department of Public Health and Paediatrics, Microbiology Division, University of Turin, Turin, Italy
Abstract: The growing threat of antimicrobial drug resistance has stimulated the search for new therapeutic alternatives, including essential oils that are now recognized for their potential antimicrobial role against microorganisms. The essential oil (EO) of Melaleuca alternifolia (Myrtaceae; Tea Tree Oil,TTO) was used early in last century to treat many pathological conditions, predominantly dermatoses (e.g., recurrent herpes labialis, acne, pustules, dandruff, and rash). Moreover, TTO has recently received much attention for its antibacterial, antifungal and antiviral properties. Since clinical experience showed that the efficacy of antimicrobial drugs depends both on their direct effect on microorganisms and on the activity of the host immune system, the aim of the study was to evaluated the influence of TTO, at subinhibitory concentrations, on intracellular killing by PMNs against Candida krusei, in comparison with anidulafungin (AND), one of the antifungal drugs used in candidiasis management. Materials/methods: A clinical C.krusei strain was used. The EO was purchased from Flora, Pisa, Italy, and analysed by GC (Drug Science and Technology Dept., University of Turin). AND was provided by Pfizer Italia. Susceptibility testing was based on the CLSI M27-A3 method, with some modifications for EOs. Intracellular killing was investigated by incubating yeasts (106 cfu/mL) and PMNs (106cells/mL) at 37°C for 30, 60, 90 min in presence of TTO sub-inhibitory concentrations (1/4 and 1/8 MIC), and 1/2MIC of AND. Killing values were expressed as Survival Index. EO/AND-free controls were included. Statistical evaluation of the differences between test and control results was performed by Tukey’s test. The cytotoxicity of various concentrations of TTO was evaluated with MTT test assay. Results: TTO was more efficacy at ⅛ MIC than ¼ MIC, with killing values higher in comparison with those observed in free-EO systems and in presence of AND, indicating that the decreasing concentrations did not cause lower candidacidal activity. Moreover, TTO at 1/4 MIC was toxic, with decreased intracellular killing values, suggesting that TTO at higher concentrations could interfere with the functionality of PMNs. Conclusions: These data show a promising potential application of TTO, as natural adjuvant against C.krusei, often resistant to conventional drugs.

Type: Review
Title:
Essential oils and mono/bi/tri-metallic nanocomposites as alternative sources to combat multidrug-resistant pathogenic microorganisms. An overview
Authors: Nagaraj Basavegowda1, Jayanta Kumar Patra2* and Kwang-Hyun Baek1*
Affiliation:
1Department of Biotechnology, Yeungnam University, Gyeongsan, Gyeongbuk 38451, Republic of Korea 2Research Institute of Biotechnology and Medical Converged Science, Dongguk University-Seoul, Goyang 10326, Republic of Korea
Abstract: Over the past few decades, many pathogenic bacteria have become resistant to existing antibiotics and a crucial problem for infectious diseases worldwide. Hence, it illustrates to search for new, efficient and alternative sources of antimicrobial agents to combat multidrug-resistant pathogenic microorganisms. Numerous studies have shown the potential of both essential oils and nanocomposites with broad spectrum of bioactivity. This review summarizes the synergistic effects of essential oils with other antimicrobial combinations such as mono-, bi-, and tri-metallic nanocomposites. The various aspects of this comprehensive review may encourage to develop new and alternative therapeutics against antibiotic resistant pathogens in the future.

Back to TopTop