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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 (30 June 2023) | Viewed by 32928

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Special Issue Editors

Dr. Paola Angelini

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Guest Editor

Department of Chemistry, Biology, and Biotechnology, University of Perugia, 06122 Perugia, Italy
Interests: biodiversity; biological activities; dermatophyte; essential oils; medicinal Plants; mushrooms; non-volatile extracts
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Prof. Dr. Roberto Venanzoni

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Department of Chemistry, Biology and Biotechnology, University of Perugia, 06121 Perugia, Italy
Interests: botany; vegatation science; biological activities; dermatophyte; plants; fungal extracts
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Dr. Giancarlo Angeles Flores

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Guest Editor

Pharmacy Department, University of Chieti, Via dei Vestini 31, 66100 Chieti, Italy
Interests: medicinal plants and fungi; dermatophytes; microorganisms; human pathogenic fungi and bacteria; antimicrobials; biological assays
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Microbial pathogenicity and other infectious diseases have been controlled by the use of commercially available antimicrobial drugs in recent years. Antimicrobial drugs have, however, been overused and misused in the general population, which led to an increase in drug resistance rates among several microorganisms. Hence in recent years, antimicrobial drug resistance has been recognized as a major global health threat. Medicinal plants are an important source of pharmacologically active secondary compounds, such as coumarins, flavonoids, phenolics, alkaloids, terpenoids, tannins, lectin, polypeptides, and polyacetylenes. Numerous articles reporting on the antimicrobial activity of plant extracts are published. Industrial hemp is one of many examples; recent studies have shown that inflorescence water extract and essential oils from this plant have antifungal activity against dermatophytes (Orlando et al. 2021). In this Special Issue dedicated to “Plant Extracts and Antimicrobials”, research papers and reviews about the research on new antimicrobial plant extracts or molecules, at a laboratory scale or at a pilot level, are welcome. The alternative use of plant extracts or compounds in food, beverage, supplements, and cosmetics could also be part of this Special Issue.

Topics particularly of interest are:

Production of plant compounds with antimicrobial properties;
Industrial applications and scaling up;
Methods to increase active compounds yield (e.g., bioelicitation);
Product extraction and characterization;
Plant tissue culture in vitro and biochemical pathways;
Bioactivity of wild specimens versus cultivated specimens;
In vitro and in vivo tests;
Microbial species and strain screening.

Dr. Paola Angelini
Prof. Roberto Venanzoni
Dr. Giancarlo Angeles Flores
Guest Editors

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Keywords

antibacterials
antifungals
antivirals
bioactive compounds
biofilms
dermatophytes
drug resistance
food
beverages and supplements
pathogenics
mode of action
plant extracts
screening
spices

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Published Papers (9 papers)

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Editorial

Jump to: Research, Review

3 pages, 166 KiB

Open AccessEditorial

Exploring Plant Extracts as a Novel Frontier in Antimicrobial Innovation: Plant Extracts and Antimicrobials

by Roberto Venanzoni, Giancarlo Angeles Flores and Paola Angelini

Microorganisms 2024, 12(3), 483; https://doi.org/10.3390/microorganisms12030483 - 27 Feb 2024

Viewed by 2373

Abstract

The scientific exploration presented in this Special Issue offers a comprehensive overview of recent advancements in the realm of plant-derived antimicrobials [...] Full article

(This article belongs to the Special Issue Plant Extracts and Antimicrobials)

Research

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17 pages, 3093 KiB

Open AccessArticle

Bioactivity and Metabolomic Profile of Extracts Derived from Mycelial Solid Cultures of Hypsizygus marmoreus

by Paola Angelini, Giancarlo Angeles Flores, Gaia Cusumano, Roberto Venanzoni, Roberto Maria Pellegrino, Gokhan Zengin, Simonetta Cristina Di Simone, Luigi Menghini and Claudio Ferrante

Microorganisms 2023, 11(10), 2552; https://doi.org/10.3390/microorganisms11102552 - 13 Oct 2023

Cited by 6 | Viewed by 2160

Abstract

The beech mushroom (Hypsizygus marmoreus) is a highly nutritious, edible medicinal mushroom native to East Asia. The present research investigated the impact of different substrates on the metabolite compositions of H. marmoreus mycelia cultivated in vitro. The substrates tested included malt extract agar, malt extract agar enriched with barley malt, and malt extract agar enriched with grape pomace. The study also assessed antimicrobial and antiradical activities of the extracts against gram-positive bacteria (Bacillus subtilis and Staphylococcus aureus), gram-negative bacteria (Escherichia coli, Salmonella typhi, and Pseudomonas aeruginosa), yeasts (Candida albicans, C. tropicalis, and C. parapsilosis), and dermatophytes (Trichophyton mentagrophytes, T. tonsurans, T. rubrum, Arthroderma quadrifidum, A. gypseum, A. curreyi, and A. insingulare). The results revealed that the H. marmoreus mycelia extracts demonstrated antibacterial and antifungal activities against the tested microorganisms. Extracts obtained from the cultivation in substrates enriched with either barley malt or grape pomace exhibited the highest antibacterial activity among all the tested bacterial strains except for P. aeruginosa. The same extracts showed the highest inhibitory effect against C. albicans and C. parapsilosis. Noteworthy, the extract from the mushroom cultivated in the substrate enriched with grape pomace also exhibited remarkable efficacy against T. mentagrophytes and T. tonsurans. Terpenoid and carbapenem compounds could be related to the antimicrobial properties of the extracts from mushrooms cultivated in substrates enriched with grape pomace. In comparison, the higher antiradical properties could be related to the content of indole compounds. In conclusion, growth substrate selection affects the nutritional and medicinal properties of H. marmoreus, making it a valuable contribution to the understanding of the cultivation of this mushroom. Full article

(This article belongs to the Special Issue Plant Extracts and Antimicrobials)

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14 pages, 3858 KiB

Open AccessArticle

Biochemical, Antioxidant Properties and Antimicrobial Activity of Steno-Endemic Origanum onites

by Kerem Canli, Mustafa Eray Bozyel, Dilay Turu, Atakan Benek, Ozcan Simsek and Ergin Murat Altuner

Microorganisms 2023, 11(8), 1987; https://doi.org/10.3390/microorganisms11081987 - 2 Aug 2023

Cited by 6 | Viewed by 1761

Abstract

Origanum onites (Lamiaceae) is an Eastern Mediterranean plant that is widely used in Turkish traditional medicine. This study aimed to investigate the biochemical composition, antimicrobial activity, and antioxidant potential of O. onites. In this study, the biochemical composition of the O. onites ethanol extract (OOEt) was analyzed using GC-MS. The antimicrobial activity was investigated using a disk diffusion test and determining minimum inhibitory concentrations (MIC) against 30 microorganism strains, including 28 bacteria (some multidrug-resistant) and 2 fungi. Additionally, the antioxidant activity was evaluated using the DPPH method. The main component identified was carvacrol. OOEt demonstrated antimicrobial activity against a wide range of tested microorganism strains. OOEt displayed the highest activity against E. faecium (a Gram-positive bacterium) at 100 µL with a 52 mm inhibition zone. Additionally, P. aeruginosa DSMZ 50071 and P. fluorescens P1, which are Gram-negative bacteria, were the most sensitive strains with a 24 mm inhibition zone in 100 µL of OOEt. The data obtained from A. baumannii (a multidrug-resistant strain) is particularly striking, as higher activity was observed compared to all positive controls. All tested fungal strains showed more effective results than positive controls. The antioxidant activity of OOEt was found to be stronger than that of the positive control, ascorbic acid. This study determined that O. onites has significant antimicrobial and antioxidant potential. Full article

(This article belongs to the Special Issue Plant Extracts and Antimicrobials)

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16 pages, 3088 KiB

Open AccessArticle

Antifungal Activity of Hop Leaf Extracts and Xanthohumol on Two Strains of Venturia inaequalis with Different Sensitivities to Triazoles

by Sophie Moureu, Justine Jacquin, Jennifer Samaillie, Caroline Deweer, Céline Rivière and Jérôme Muchembled

Microorganisms 2023, 11(6), 1605; https://doi.org/10.3390/microorganisms11061605 - 17 Jun 2023

Cited by 6 | Viewed by 2001

Abstract

Hop cones are well-known for their antimicrobial properties, attributed to their specialized metabolites. Thus, this study aimed to determine the in vitro antifungal activity of different hop parts, including by-products such as leaves and stems, and some metabolites against Venturia inaequalis, the causal agent of apple scab. For each plant part, two types of extracts, a crude hydro-ethanolic extract and a dichloromethane sub-extract, were tested on spore germination of two strains with different sensitivities to triazole fungicides. Both extracts of cones, leaves and stems were able to inhibit the two strains, whereas rhizomes did not show activity. The apolar sub-extract of leaves appeared as the most active modality tested with half maximal inhibitory concentrations (IC₅₀) of 5 and 10.5 mg·L⁻¹ on the sensitive strain and the strain with reduced sensitivity, respectively. Differences in activity level between strains were noticed for all active modalities tested. Sub-extracts of leaves were then separated into seven fractions by preparative HPLC and tested on V. inaequalis. One fraction, containing xanthohumol, was especially active on both strains. This prenylated chalcone was then purified by preparative HPLC and showed significant activity against both strains, with IC₅₀ of 1.6 and 5.1 mg·L⁻¹. Therefore, xanthohumol seems to be a promising compound to control V. inaequalis. Full article

(This article belongs to the Special Issue Plant Extracts and Antimicrobials)

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16 pages, 6539 KiB

Open AccessArticle

The Antifungal Properties of Tamarix aphylla Extract against Some Plant Pathogenic Fungi

by Fatimah Al-Otibi, Ghaida A. Moria, Raedah I. Alharbi, Mohamed T. Yassin and Abdulaziz A. Al-Askar

Microorganisms 2023, 11(1), 127; https://doi.org/10.3390/microorganisms11010127 - 4 Jan 2023

Cited by 9 | Viewed by 3516

Abstract

Tamarix aphylla is a Saudi herb, which possesses antimicrobial properties and potentially introduces a solution to the subsequent dilemma caused by agrochemicals and antifungal misuse. The current study aimed to assess the fungicidal properties of water and ethanolic extracts of T. aphylla leaves against Macrophomina phaseolina, Curvularia spicifera, and Fusarium spp. The chemical composition of T. aphylla was evaluated by gas chromatography/mass spectrometry technique (GC–MS) and Fourier-transform infrared spectroscopy (FTIR). The antifungal assay assessed the fungal growth inhibition using the poisoned food technique. Scanning and transmission electron microscopy (SEM and TEM) were used to evaluate the structural changes induced in the fungal species post-treatment by T. aphylla. FTIR and GC–MS analysis revealed that T. aphylla extracts were rich in aromatic and volatile compounds, such as Benzeneselenol, Gibberellic acid, and Triaziquone, which proved multiple antifungal properties. The results showed significant inhibition in the growth of all species (p < 0.05) except for F. moniliforme, where the water extract induced the highest mycelial growth inhibition at the dose of 30%. The highest inhibition was for M. phaseolina treated with the water extract (36.25 ± 1.06 mm, p < 0.001) and C. spicifera, treated with the ethanolic extract (27.25 ± 1.77 mm, p < 0.05), as compared to the untreated control and the positive control of Ridomol. SEM and TEM revealed some ultrastructural changes within the fungal growth of treated M. phaseolina, which included the thickening and mild rupture of mycelia. Those findings suggested the robust antifungal properties of T. aphylla against some filamentous fungi. The phenolic composition illustrated the potential fungicidal properties of T. aphylla. Additional studies are required to focus on more antimicrobial properties of T. aphylla against other species, particularly those that might benefit the medical field. Full article

(This article belongs to the Special Issue Plant Extracts and Antimicrobials)

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16 pages, 5182 KiB

Open AccessArticle

Microemulsion of Cinnamon Essential Oil Formulated with Tea Polyphenols, Gallic Acid, and Tween 80: Antimicrobial Properties, Stability and Mechanism of Action

by Wei Wang, Yin-Feng Chen, Ze-Feng Wei, Jing-Jing Jiang, Jia-Qian Peng, Qi-Tong He, Wen-Ying Xu and Hui-Min Liu

Microorganisms 2023, 11(1), 2; https://doi.org/10.3390/microorganisms11010002 - 20 Dec 2022

Cited by 16 | Viewed by 3976

Abstract

The objective of this article was to combine tea polyphenols, gallic acid, and cinnamon essential oil to construct a natural extract-complex microemulsion system (NMs) with good antibacterial activity, antioxidant activity, and stability, as well as low irritation. NMs were characterized by particle size distribution, electrical conductivity, and light transmittance. The stability, as well as the antimicrobial, antioxidant, irritation, and antimicrobial mechanisms, of NMs were also studied. The results showed that NMs had a significant antimicrobial function against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Candida albicans and Aspergillus brasiliensis. The minimum inhibitory concentrations were 156 μg/mL, 62.5 μg/mL, 125 μg/mL, 250 μg/mL, and 125 μg/mL, respectively. Through the cell membrane permeability test and growth curve test of bacteria and fungi, we concluded that the NMs’ mechanism of action on bacteria and fungi could be interpreted as NMs mainly altering the permeability of cell membranes to inhibit the growth of bacteria and fungi. The results of this study have important implications for utilizing plant extracts as natural preservatives for food and cosmetics. Full article

(This article belongs to the Special Issue Plant Extracts and Antimicrobials)

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17 pages, 653 KiB

Open AccessArticle

Towards Green Strategies of Food Security: Antibacterial Synergy of Essential Oils from Thymus vulgaris and Syzygium aromaticum to Inhibit Escherichia coli and Staphylococcus aureus Pathogenic Food Isolates

by Daniela Sateriale, Giuseppina Forgione, Giuseppa Anna De Cristofaro, Serena Facchiano, Floriana Boscaino, Chiara Pagliuca, Roberta Colicchio, Paola Salvatore, Marina Paolucci and Caterina Pagliarulo

Microorganisms 2022, 10(12), 2446; https://doi.org/10.3390/microorganisms10122446 - 10 Dec 2022

Cited by 18 | Viewed by 5215

Abstract

Foodborne diseases continue to represent an important public health issue. The control of food spoilage and pathogenic microorganisms is achieved mainly by synthetic chemicals, unfortunately associated to several undesirable aspects. The growing requirement for new and safe alternative strategies has resulted in the research of agents from natural sources with antimicrobial properties, such as essential oils (EOs). This study’s purpose was to define the antibacterial profile of thyme (Thymus vulgaris) and cloves (Syzygium aromaticum) essential oils against both Gram-positive and Gram-negative important foodborne pathogenic bacteria. Gas chromatography mass spectrometry analysis was performed for EOs’ chemical composition. Qualitative in vitro antimicrobial assays (i.e., agar well diffusion method and disk-volatilization method) allowed for verification of the efficacy of EOs, used individually and in binary combination and both in liquid and vapor phase, against Staphylococcus aureus and Escherichia coli food isolates. Minimal inhibitory concentrations and minimal bactericidal concentration values have been used to quantitatively measure the antibacterial activity of EOs, while the fractional inhibitory concentration index has been considered as a predictor of in vitro antibacterial synergistic effects. The microbiological tests suggest that thyme and cloves EOs, rich in bioactive compounds, are able to inhibit the growth of tested foodborne bacteria, especially in vapor phase, also with synergistic effects. Results provide evidence to consider the tested essential oils as promising sources for development of new, broad-spectrum, green food preservatives. Full article

(This article belongs to the Special Issue Plant Extracts and Antimicrobials)

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24 pages, 4927 KiB

Open AccessArticle

Antibacterial and Anti-Inflammatory Activities of Thymus vulgaris Essential Oil Nanoemulsion on Acne Vulgaris

by Farah M. Abdelhamed, Nourtan F. Abdeltawab, Marwa T. ElRakaiby, Rehab N. Shamma and Nayera A. Moneib

Microorganisms 2022, 10(9), 1874; https://doi.org/10.3390/microorganisms10091874 - 19 Sep 2022

Cited by 27 | Viewed by 7271

Abstract

Antibiotics are frequently used in acne treatment and their prolonged use has led to an emergence of resistance. This study aimed to investigate the use of natural antimicrobials as an alternative therapy. The antimicrobial and anti-inflammatory activities of five commonly used essential oils (EOs) (tea tree, clove, thyme, mentha and basil EOs), and their possible mechanisms of action against Cutibacterium acnes and Staphylococcus epidermidis, were explored. The effect of the most potent EO on membrane permeability was elucidated and its anti-inflammatory action, when formulated as nanoemulsion, was tested in an in vivo acne model. The in vitro studies showed that thyme EO had the most potent antimicrobial and antibiofilm activity, with phenolics and terpenoids as main antimicrobial constituents of EO. Thyme EO affected cell membrane permeability of both bacterial species, evident by the detection of the leakage of intracellular ions and membrane integrity by the leakage of nucleic acids. Morphological alteration in bacterial cells was confirmed by transmission electron microscopy. Thyme EO nanoemulsion led to the suppression of an inflammatory response in acne animal models along with a bacterial load decrease and positive histopathological changes. Collectively, thyme EO nanoemulsion showed potent antimicrobial and anti-inflammatory effects compared to the reference antibiotics, suggesting its effectiveness as a natural alternative in acne treatment. Full article

(This article belongs to the Special Issue Plant Extracts and Antimicrobials)

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Review

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17 pages, 839 KiB

Open AccessReview

Antimicrobial Efficiency of Pistacia lentiscus L. Derivates against Oral Biofilm-Associated Diseases—A Narrative Review

by Egle Patrizia Milia, Luigi Sardellitti and Sigrun Eick

Microorganisms 2023, 11(6), 1378; https://doi.org/10.3390/microorganisms11061378 - 24 May 2023

Cited by 7 | Viewed by 2926

Abstract

Pistacia lentiscus L. (PlL) has been used for centuries in traditional medicine. The richness in antimicrobial biomolecules of Pll derivates can represent an alternative to chemically formulated agents used against oral infections. This review summarizes the knowledge on the antimicrobial activity of PlL essential oil (EO), extracts, and mastic resin against microorganisms being of relevance in oral biofilm-associated diseases. Results demonstrated that the potential of PlL polyphenol extracts has led to increasing scientific interest. In fact, the extracts are a significantly more effective agent than the other PlL derivates. The positive findings regarding the inhibition of periodontal pathogens and C. albicans, together with the antioxidant activity and the reduction of the inflammatory responses, suggest the use of the extracts in the prevention and/or reversal of intraoral dysbiosis. Toothpaste, mouthwashes, and local delivery devices could be effective in the clinical management of these oral diseases. Full article

(This article belongs to the Special Issue Plant Extracts and Antimicrobials)

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