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Antimicrobial Activity of Essential Oils and Hydrolates

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A special issue of Microorganisms (ISSN 2076-2607). This special issue belongs to the section "Antimicrobial Agents and Resistance".

Deadline for manuscript submissions: closed (31 March 2022) | Viewed by 26153

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Special Issue Editors

Dr. Francesca Bugli

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Guest Editor

1. Dipartimento di Scienze Biotecnologiche di Base, Cliniche Intensivologiche e Perioperatorie, Università Cattolica del Sacro Cuore, Roma, Italy
2. Dipartimento di Scienze di Laboratorio e Infettivologiche, Fondazione Policlinico Universitario A. Gemelli IRCCS, Roma, Italy
Interests: natural substances; essential oils; antimicrobial activity; antimicrobial resistance; antioxidant activity; synergism between natural substances and conventional active molecules; probiotic and prebiotic activity; natural compounds as support for treatments in intensive veterinary fields
Special Issues, Collections and Topics in MDPI journals

Dr. Maura Di Vito

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Guest Editor

Dipartimento di Scienze Biotecnologiche di Base, Cliniche Intensivologiche e Perioperatorie, Università Cattolica del Sacro Cuore, 00168 Rome, Italy
Interests: essential oils; microbiology; human physio-pathology
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Antimicrobial resistance is known to be one of the most complex global health challenges today. As reported by the WHO, it is very important to find new candidates for the development of future effective anti-infective therapies. Essential oils (EO) and hydrolates (Hys) are, of all natural substances, the best candidates to draw on to combat antibiotic resistance and are therefore considered of great interest nowadays in both scientific and pharmaceutical research. Today, despite the significant scientific evidence of the efficacy of EOs, in the field of infectious diseases, their use alone or in synergy with conventional medicine is hindered. In fact, there is still the absence of large-scale efficacy studies to obtain evidence, both in vitro, with standardized, rapid and easy-to-perform methods as diagnostic tests that can be used to start more targeted pharmacological experiments, and in vivo, with randomized clinical trials. Therefore, the main objective of this Special Issue of Microorganisms is to select, in vivo or in vitro, articles on the antimicrobial efficacy of EOs and Hys potentially active in the fight against bacteria, fungi, viruses and parasites potentially dangerous for human, animal and plant health. Articles developed in other contexts (example: food production, protection of cultural heritage or sanitation of confined environments) will also be welcome, provided that they are aimed at evaluating the anti-microbial action of OEs and/or Hys, and to standardize models of diffusion of OEs in relevant confined environments.

Dr. Francesca Bugli
Dr. Maura Di Vito
Guest Editors

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 submissions that pass pre-check are 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. Microorganisms is an international peer-reviewed open access monthly 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 2700 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
hydrolates
human heath
veterinary
phytopathology
cultural heritage

Published Papers (9 papers)

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Research

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13 pages, 5294 KiB

Open AccessArticle

Unraveling the Antimicrobial Effectiveness of Coridothymus capitatus Hydrolate against Listeria monocytogenes in Environmental Conditions Encountered in Foods: An In Vitro Study

by Francesco Buccioni, Chiara Purgatorio, Francesca Maggio, Stefania Garzoli, Chiara Rossi, Luca Valbonetti, Antonello Paparella and Annalisa Serio

Microorganisms 2022, 10(5), 920; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms10050920 - 27 Apr 2022

Cited by 4 | Viewed by 1502

Abstract

The increased resistance of bacteria to antimicrobials, as well as the growing interest in innovative and sustainable alternatives to traditional food additives, are driving research towards the use of natural food preservatives. Among these, hydrolates (HYs) have gained attention as “mild” alternatives to conventional antimicrobial compounds. In this study, the response of L. monocytogenes ATCC 7644 exposed to increasing concentrations of Coridothymus capitatus HY (CHY) for 1 h at 37 °C was evaluated by means of Phenotype Microarray, modelling the kinetic data obtained by inoculating control and treated cells into GEN III microplates, after CHY removal. The results revealed differences concerning the growth dynamics in environmental conditions commonly encountered in food processing environments (different carbon sources, pH 6.0, pH 5.0, 1–8% NaCl). More specifically, for treated cells, the lag phase was extended, the growth rate was slowed down and, in most cases, the maximum concentration was diminished, suggesting the persistence of stress even after CHY removal. Confocal Laser Scanner Microscopy evidenced a diffuse aggregation and suffering of the treated cells, as a response to the stress encountered. In conclusion, the treatment with HY caused a stressing effect that persisted after its removal. The results suggest the potential of CHY application to control L. monocytogenes in food environments. Full article

(This article belongs to the Special Issue Antimicrobial Activity of Essential Oils and Hydrolates)

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21 pages, 2982 KiB

Open AccessArticle

Potential Applications of Essential Oils for Environmental Sanitization and Antimicrobial Treatment of Intensive Livestock Infections

by Melinda Mariotti, Giulia Lombardini, Silvia Rizzo, Donatella Scarafile, Monica Modesto, Eleonora Truzzi, Stefania Benvenuti, Alberto Elmi, Martina Bertocchi, Laura Fiorentini, Lorenzo Gambi, Maurizio Scozzoli and Paola Mattarelli

Microorganisms 2022, 10(4), 822; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms10040822 - 15 Apr 2022

Cited by 13 | Viewed by 2443

Abstract

The extensive use of antibiotics has contributed to the current antibiotic resistance crisis. Livestock infections of Salmonella spp, Clostridium spp. and E. coli antimicrobial-resistant bacteria represent a public threat to human and animal health. To reduce the incidence of these zoonoses, essential oils (EOs) could be effective antibiotic alternatives. This study aims at identifying EOs safe for use, effective both in complementary therapy and in the environmental sanitization of intensive farming. Natural products were chemo-characterized by gas chromatography. Three S. Typhimurium, three C. perfringens and four E. coli strains isolated from poultry and swine farms were used to assess the antimicrobial properties of nine EOs and a modified GR-OLI (mGR-OLI). The toxicity of the most effective ones (Cinnamomum zeylanicum, Cz; Origanum vulgare, Ov) was also evaluated on porcine spermatozoa and Galleria mellonella larvae. Cz, Ov and mGR-OLI showed the strongest antimicrobial activity; their volatile components were also able to significantly inhibit the growth of tested strains. In vitro, Ov toxicity was slightly lower than Cz, while it showed no toxicity on G. mellonella larvae. In conclusion, the study confirms the importance of evaluating natural products to consolidate the idea of safe EO applications in reducing and preventing intensive livestock infections. Full article

(This article belongs to the Special Issue Antimicrobial Activity of Essential Oils and Hydrolates)

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19 pages, 400 KiB

Open AccessArticle

Evaluation of the Antimicrobial and Antivirulent Potential of Essential Oils Isolated from Juniperus oxycedrus L. ssp. macrocarpa Aerial Parts

by Gabriella Spengler, Márió Gajdács, Matthew Gavino Donadu, Marianna Usai, Mauro Marchetti, Marco Ferrari, Vittorio Mazzarello, Stefania Zanetti, Fruzsina Nagy and Renátó Kovács

Microorganisms 2022, 10(4), 758; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms10040758 - 31 Mar 2022

Cited by 29 | Viewed by 3065

Abstract

As a consequence of the worsening situation with multidrug-resistant (MDR) pathogens and a disparity in the commercialization of novel antimicrobial agents, scientists have been prompted to seek out new compounds with antimicrobial activity from a wide range of sources, including medicinal plants. In the present study, the antibacterial, antifungal, anti-virulence, and resistance-modulating properties of the essential oil from the Sardinian endemic Juniperus oxycedrus L. ssp. macrocarpa aerial parts were evaluated. The GC/MS analysis showed that the main compounds in the oil were α-pinene (56.63 ± 0.24%), limonene (14.66 ± 0.11%), and β-pinene (13.42 ± 0.09%). The essential oil showed potent antibacterial activity against Gram-positive bacteria (0.25–2 v/v%) and Salmonella spp. (4 v/v%). The strongest fungicidal activity was recorded against Candida auris sessile cells (median FICI was 0.088) but not against C. albicans biofilms (median FICI was 1). The oil showed potent efflux pump inhibitory properties in the case of Staphylococcus aureus and Escherichia coli. The therapeutic potential of Juniperus may be promising for future more extensive research and in vivo tests to develop new drugs against antibiotic and antifungal resistance. Full article

(This article belongs to the Special Issue Antimicrobial Activity of Essential Oils and Hydrolates)

19 pages, 5512 KiB

Open AccessArticle

Essential Oils and Hydrolates: Potential Tools for Defense against Bacterial Plant Pathogens

by Maria Rita Proto, Enrico Biondi, David Baldo, Matilde Levoni, Gianfranco Filippini, Monica Modesto, Maura Di Vito, Francesca Bugli, Claudio Ratti, Paola Minardi and Paola Mattarelli

Microorganisms 2022, 10(4), 702; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms10040702 - 24 Mar 2022

Cited by 7 | Viewed by 2700

Abstract

The essential oils (EOs) of Origanum compactum and Satureja montana chemotyped (CT) at carvacrol, two Thymus vulgaris CT at thujanol and thymol, and Hydrolates (Hys) of S. montana and Citrus aurantium var. amara were chosen for studying their bactericidal efficacy against few phytobacterial pathogens. The Minimal Inhibitory Concentration (MIC) and Bactericidal Concentration (MBC) were found by microdilution assay. The essential oils of O. compactum (MBC 0.06% v/v), T. vulgaris CT thymol (MBC 0.06% v/v), and Hy of C. aurantium (MBC 6.25% v/v) resulted in being the most effective against Erwinia amylovora; thus, they were used as starting concentrations for ex vivo assays. Despite the great in vitro effectiveness, the disease incidence and the population dynamic ex vivo assays showed no significant results. On the other hand, EO of O. compactum and Hy of C. aurantium (at 0.03% and 4.5% v/v, respectively) showed resistance induction in tomato plants against Xanthomonas vesicatoria infections; both treatments resulted in approximately 50% protection. In conclusion, EOs and Hys could be promising tools for agricultural defense, but further studies will be necessary to stabilize the EOs emulsions, while Hys application could be an effective method to prevent bacterial diseases when used as resistance inducer by pre-transplantation treatment at roots. Full article

(This article belongs to the Special Issue Antimicrobial Activity of Essential Oils and Hydrolates)

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14 pages, 1661 KiB

Open AccessArticle

Reduction of Bacterial Enteric Pathogens and Hygiene Indicator Bacteria on Tomato Skin Surfaces by a Polymeric Nanoparticle-Loaded Plant-Derived Antimicrobial

by Keila L. Perez-Lewis, Yagmur Yegin, Jun K. Oh, Alejandro Castillo, Luis Cisneros-Zevallos, Chris R. Kerth, Mustafa Akbulut and Thomas M. Taylor

Microorganisms 2022, 10(2), 448; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms10020448 - 15 Feb 2022

Viewed by 2442

Abstract

This study determined Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium survival on tomato skins as a function of sanitization treatment, under three differing contamination and sanitization scenarios. Sanitizing treatments consisted of the plant-derived antimicrobial (PDA) geraniol (0.5 wt.%) emulsified in the polymeric surfactant Pluronic F-127 (GNP), 0.5 wt.% unencapsulated geraniol (UG), 200 mg/L hypochlorous acid at pH 7.0 (HOCl), and a sterile distilled water wash (CON). Experimental contamination and sanitization scenarios tested were: (1) pathogen inoculation preceded by treatment; (2) the pathogen was inoculated onto samples twice with a sanitizing treatment applied in between inoculations; and (3) pathogen inoculation followed by sanitizing treatment. Reductions in counts of surviving pathogens were dependent on the sanitizing treatment, the storage period, or the interaction of these independent/main effects. GNP treatment yielded the greatest reductions in pathogen counts on tomato skins; pathogen survivor counts following GNP treatment were consistently statistically lower than those achieved by HOCl or UG treatments (p < 0.05). GNP treatment provided greatest pathogen reduction under differing conditions of pre- and/or post-harvest cross-contamination, and reduced hygiene-indicating microbes the most of all treatments on non-inoculated samples. Encapsulated geraniol can reduce the risk of pathogen transmission on tomato fruit, reducing food safety hazard risks for tomato consumers. Full article

(This article belongs to the Special Issue Antimicrobial Activity of Essential Oils and Hydrolates)

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11 pages, 618 KiB

Open AccessArticle

Anti-Mold Effectiveness of a Green Emulsion Based on Citrus aurantium Hydrolate and Cinnamomum zeylanicum Essential Oil for the Modern Paintings Restoration

by Maura Di Vito, Lara Vergari, Melinda Mariotti, Maria Rita Proto, Lorenzo Barbanti, Stefania Garzoli, Maurizio Sanguinetti, Luigia Sabatini, Alice Peduzzi, Maria Grazia Bellardi, Paola Mattarelli, Francesca Bugli and Daphne De Luca

Microorganisms 2022, 10(2), 205; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms10020205 - 19 Jan 2022

Cited by 5 | Viewed by 2317

Abstract

A modern painting is characterized by multi-material bases extremely exposed to biodeteriogenic attacks. The aim of this work was to test the antifungal effectiveness of a natural, eco-friendly, and safe emulsion based on Citrus aurantium L. var. amara hydrolate and Cinnamomum zeylanicum Blume (from bark) essential oil, named “Zeylantium green emulsion” (Zege), on modern paintings. Colored unaged and aged canvas samples, performed with modern techniques (acrylic, vinylic and alkyd), were used to test in vitro both the antifungal effectiveness of Zege and its impact on the chemical–physical characteristics. Microbiological tests were performed according to the EUCAST international guidelines. pH measurements and colorimetric analysis were performed on unaged and aged canvases before and after Zege spray treatment. Finally, in situ tests were performed using the spray emulsion on canvas samples obtained from Ilaria Margutti’s modern artwork, which had been colonized by molds. Microbiological tests on canvas prototypes showed a time- and dose-dependent effectiveness of the Zege spray. None of the techniques underwent relevant changes in pH. Only the acrylic colors were unaffected in the colorimetric analysis, among all colored unaged or aged canvases. Tests made with modern artwork samples confirmed the in situ antifungal effectiveness. The Zege spray showed encouraging results in regard to the use of this formulation in the restoration of modern paintings. Full article

(This article belongs to the Special Issue Antimicrobial Activity of Essential Oils and Hydrolates)

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18 pages, 4555 KiB

Open AccessArticle

Susceptibility of Fluconazole-Resistant Candida albicans to Thyme Essential Oil

by Najla A Alshaikh and Kahkashan Perveen

Microorganisms 2021, 9(12), 2454; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms9122454 - 28 Nov 2021

Cited by 8 | Viewed by 5090

Abstract

Candida spp. is the most common microbial pathogen in fungal infections. There has been a tremendous increase in cases of candidiasis, especially among critically ill non-neutropenic patients. Candida albicans’ isolates were procured from the Prince Sultan Military Hospital, Riyadh, KSA. The isolates were characterized for their identification using CHROMagar, carbohydrate metabolism, germ tube formation, and RAPD-PCR techniques. The essential oil of Thymus vulgaris was obtained by hydro-distillation and characterized to decipher the major bioactive phytoconstituents. The antifungal activity of the thyme essential oil (TEO) was evaluated against fluconazole-resistant C. albicans isolates. The major phytocomponents identified by GC/MS were thymol (68.1%) followed by γ-terpinene (8.9%), cymol (7.7%), caryophyllene (1.1%), linalool (1.4%). The TEO successfully reduced the growth of C. albicans isolates. At very low doses, the TEO proved to be fungi static and fungicidal. TEO also effectively inhibited the germ tube formation and budging of fungal pathogens. The time kill assays have shown that TEO was more effective against drug resistant clinical isolates than fluconazole. This study provides an array of experimental evidence regarding the therapeutic efficacy of TEO against the drug-resistant clinical isolates of C. albicans. The findings may be used in the development of a new antifungal agent accordingly. Full article

(This article belongs to the Special Issue Antimicrobial Activity of Essential Oils and Hydrolates)

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17 pages, 5219 KiB

Open AccessArticle

Anti-Virulence Properties of Coridothymus capitatus Essential Oil against Pseudomonas aeruginosa Clinical Isolates from Cystic Fibrosis Patients

by Gianluca Vrenna, Marco Artini, Rino Ragno, Michela Relucenti, Ersilia Vita Fiscarelli, Vanessa Tuccio Guarna Assanti, Rosanna Papa and Laura Selan

Microorganisms 2021, 9(11), 2257; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms9112257 - 29 Oct 2021

Cited by 11 | Viewed by 1763

Abstract

Pseudomonas aeruginosa is an opportunistic pathogen responsible for nosocomial infections, and is often involved in airway infections of cystic fibrosis (CF) patients. P. aeruginosa virulence is related to its ability to form biofilm, trigger different types of motilities, and produce toxins (for example, bacterial pigments). In this scenario, essential oils (EOs) have gained notoriety for their role in phenotype modulation, including virulence modulation. Among different EOs previously analyzed, herein we investigated the activity of Coridothymus capitatus EO (CCEO) against specific virulence factors produced by P. aeruginosa isolated from CF patients. CCEO showed inhibition of new biofilm formation and reduction in mature biofilm in about half of the tested strains. On selected strains, SEM analysis provided interesting information regarding CCEO action in a pre-adhesion assay. CCEO treatment showed a dramatic modification of the extracellular matrix (ECM) structure. Our results clearly showed a drastic reduction in pyocyanin production (between 84% and 100%) for all tested strains in the presence of CCEO. Finally, CCEO was also able to strongly affect P. aeruginosa swarming and swimming motility for almost all tested strains. In consideration of the novel results obtained on clinical strains isolated from CF patients, CCEO may be a potential candidate to limit P. aeruginosa virulence. Full article

(This article belongs to the Special Issue Antimicrobial Activity of Essential Oils and Hydrolates)

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Review

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24 pages, 2018 KiB

Open AccessReview

Applications of Essential Oils as Antibacterial Agents in Minimally Processed Fruits and Vegetables—A Review

by Maria Isabel S. Santos, Cátia Marques, Joana Mota, Laurentina Pedroso and Ana Lima

Microorganisms 2022, 10(4), 760; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms10040760 - 31 Mar 2022

Cited by 19 | Viewed by 3527

Abstract

Microbial foodborne diseases are a major health concern. In this regard, one of the major risk factors is related to consumer preferences for “ready-to-eat” or minimally processed (MP) fruits and vegetables. Essential oil (EO) is a viable alternative used to reduce pathogenic bacteria and increase the shelf-life of MP foods, due to the health risks associated with food chlorine. Indeed, there has been increased interest in using EO in fresh produce. However, more information about EO applications in MP foods is necessary. For instance, although in vitro tests have defined EO as a valuable antimicrobial agent, its practical use in MP foods can be hampered by unrealistic concentrations, as most studies focus on growth reductions instead of bactericidal activity, which, in the case of MP foods, is of utmost importance. The present review focuses on the effects of EO in MP food pathogens, including the more realistic applications. Overall, due to this type of information, EO could be better regarded as an “added value” to the food industry. Full article

(This article belongs to the Special Issue Antimicrobial Activity of Essential Oils and Hydrolates)

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