Proton pumping ATPase mediated fungicidal activity of two essential oil components

Essential Oils of Mentha arvensis and Cinnamomum cassia Exhibit Distinct Antibacterial Activity at Different Temperatures In Vitro and on Chicken Skin

The bacterial contamination of meat is a global concern, especially for the risk of Salmonella infection that can lead to health issues. Artificial antibacterial compounds used to preserve fresh meat can have negative health effects. We investigated the potential of natural essential oils (EOs), namely Mentha arvensis (mint) and Cinnamomum cassia (cinnamon) EOs, to prevent contamination of the food pathogen, Salmonella enterica subsp. enterica serotype Typhimurium, in vitro and on chicken skin. The gas chromatography-mass spectrometry (GC-MS) technique was used to determine the compositions of mint EO (MEO) and cinnamon EO (CEO); the most abundant compound in MEO was menthol (68.61%), and the most abundant compound was cinnamaldehyde (83.32%) in CEO. The antibacterial activity of MEO and CEO were examined in vapor and direct contact with S. typhimurium at temperatures of 4 °C, 25 °C, and 37 °C. The minimal inhibitory concentration at 37 °C for MEO and CEO reached 20.83 µL/mL, and the minimal bactericidal concentration of CEO was the same, while for MEO, it was two-fold higher. We report that in most tested conditions in experiments performed in vitro and on chicken skin, CEO exhibits a stronger antibacterial effect than MEO. In the vapor phase, MEO was more effective against S. typhimurium than CEO at 4 °C. In direct contact, the growth of S. typhimurium was inhibited more efficiently by MEO than CEO at small concentrations and a longer exposure time at 37 °C. The exploration of CEO and MEO employment for the inhibition of Salmonella bacteria at different temperatures and conditions expands the possibilities of developing more environment- and consumer-friendly antibacterial protection for raw meat.

Chemo-enzymatic synthesis and biological activity evaluation of propenylbenzene derivatives

Propenylbenzenes, including isosafrole, anethole, isoeugenol, and their derivatives, are natural compounds found in essential oils from various plants. Compounds of this group are important and valuable, and are used in the flavour and fragrance industries as well as the pharmaceutical and cosmetic industries. The aim of this study was to develop an efficient process for synthesising oxygenated derivatives of these compounds and evaluate their potential biological activities. In this paper, we propose a two-step chemo-enzymatic method. The first step involves the synthesis of corresponding diols 1b-5b from propenylbenzenes 1a-5avia lipase catalysed epoxidation followed by epoxide hydrolysis. The second step involves the microbial oxidation of a diasteroisomeric mixture of diols 1b-5b to yield the corresponding hydroxy ketones 1c-4c, which in this study was performed on a preparative scale using Dietzia sp. DSM44016, Rhodococcus erythropolis DSM44534, R. erythropolis PCM2150, and Rhodococcus ruber PCM2166. Application of scaled-up processes allowed to obtain hydroxy ketones 1-4c with the following yield range 36-62.5%. The propenylbenzene derivatives thus obtained and the starting compounds were tested for various biological activities, including antimicrobial, antioxidant, haemolytic, and anticancer activities, and their impact on membrane fluidity. Fungistatic activity assay against selected strains of Candida albicans results in MIC₅₀ value varied from 37 to 124 μg/mL for compounds 1a, 3a-c, 4a,b, and 5a,b. The highest antiradical activity was shown by propenylbenzenes 1-5a with a double bond in their structure with EC₅₀ value ranged from 19 to 31 μg/mL. Haemolytic activity assay showed no cytotoxicity of the tested compounds on human RBCs whereas, compounds 2b-4b and 2c-4c affected the fluidity of the RBCs membrane. The tested compounds depending on their concentration showed different antiproliferative activity against HepG2, Caco-2, and MG63. The results indicate the potential utility of these compounds as fungistatics, antioxidants, and proliferation inhibitors of selected cell lines.

Isoeugenol affects expression pattern of conidial hydrophobin gene RodA and transcriptional regulators MedA and SomA responsible for adherence and biofilm formation in Aspergillus fumigatus

Aspergillus fumigatus is one of the major pathogenic fungal species, causing life-threatening infections. Due to a limited spectrum of available antifungals, exploration of new drug targets as well as potential antifungal molecules has become pertinent. Rodlet layer plays an important role in adherence of fungal conidia to hydrophobic cell surfaces in host, which also leads to A. fumigatus biofilm formation, contributing factor to fungal pathogenicity. From decades, natural sources have been known for the development of new active molecules. The present study investigates effect of isoeugenol on genes responsible for hydrophobins (RodA), adhesion as well as biofilm formation (MedA and SomA) of A. fumigatus. Minimum inhibitory concentrations (MIC and IC₅₀) of isoeugenol against A. fumigatus were determined using broth microdilution assay. The IC₅₀ results showed reduced hydrophobicity and biofilm formation as well as eradication after treatment with the compound and electron micrograph data corroborated these findings. The qRT-PCR showed a significant downregulation of genes RodA, MedA, SomA and pksP involved in hydrophobicity and biofilm formation. SwissADME studies potentiated drug-like propensity for isoeugenol which formed four hydrogen bonds with low binding energy (− 4.54 kcal/mol) at the catalytic site of RodA protein studied via AutoDock4. Hence, the findings conclude that isoeugenol inhibits conidial hydrophobicity and biofilm formation of A. fumigatus and further investigations are warranted in this direction.

Essential oils and their nanoformulations as green preservatives to boost food safety against mycotoxin contamination of food commodities: a review

Postharvest food spoilage due to fungal and mycotoxin contamination is a major challenge in tropical countries, leading to severe adverse effects on human health. Because of the negative effects of synthetic preservatives on both human health and the environment, it has been recommended that chemicals that have a botanical origin, with an eco-friendly nature and a favorable safety profile, should be used as green preservatives. Recently, the food industry and consumers have been shifting drastically towards green consumerism because of their increased concerns about health and the environment. Among different plant-based products, essential oils (EOs) and their bioactive components are strongly preferred as antimicrobial food preservatives. Despite having potent antimicrobial efficacy and preservation potential against fungal and mycotoxin contamination, essential oils and their bioactive components have limited practical applicability caused by their high volatility and their instability, implying the development of techniques to overcome the challenges associated with EO application. Essential oils and their bioactive components are promising alternatives to synthetic preservatives. To overcome challenges associated with EOs, nanotechnology has emerged as a novel technology in the food industries. Nanoencapsulation may boost the preservative potential of different essential oils by improving their solubility, stability, and targeted sustainable release. Nanoencapsulation of EOs is therefore currently being practiced to improve the stability and bioactivity of natural products. The present review has dealt extensively with the application of EOs and their nanoformulated products encapsulated in suitable polymeric matrices, so as to recommend them as novel green preservatives against foodborne molds and mycotoxin-induced deterioration of stored food commodities. © 2021 Society of Chemical Industry.

Antifungal Activity of Novel Formulations Based on Terpenoid Prodrugs against C. albicans in a Mouse Model

Carvacrol (CAR), a phenolic monoterpenoid, has been extensively investigated for its antimicrobial and antifungal activity. As a result of its poor physicochemical properties, water soluble carvacrol prodrugs (WSCPs) with improved water solubility were previously synthesized and found to possess antimicrobial activity. Here, three novel CAR analogs, WSCP1, WSCP2, and WSCP3, were tested against fluconazole (FLU)-sensitive and -resistant strains where they showed greater antifungal activity than CAR against C. albicans. The probable mechanism by which the CAR prodrugs exert the antifungal activity was studied. Results from medium acidification assays demonstrated that the CAR and its synthetically designed prodrugs inhibit the yeast plasma membrane H+-ATPase (Pma1p), an essential target in fungi. In other words, in vitro data indicated that CAR analogs can prove to be a better alternative to CAR considering their improved water solubility. In addition, CAR and WSCP1 were developed into intravaginal formulations and administered at test doses of 50 mg/kg in a mouse model of vulvovaginal candidiasis (VVC). Whereas the CAR and WSCP1 formulations both exhibited antifungal efficacy in the mouse model of VVC, the WSCP1 formulation was superior to CAR, showing a remarkable decrease in infection by ~120-fold compared to the control (infected, untreated animals). Taken together, a synthetically designed prodrug of CAR, namely WSCP1, proved to be a possible solution for poorly water-soluble drugs, an inhibitor of an essential yeast pump in vitro and an effective and promising antifungal agent in vivo.

Synthesis and Antifungal Activities of Cinnamaldehyde Derivatives against Penicillium digitatum Causing Citrus Green Mold

Penicillium digitatum (green mold) is pathogenic fungi and causes citrus fruit postharvest rotting that leads to huge economic losses across the world. The current study was aimed to develop a new derivative of cinnamaldehyde (4-methoxycinnamaldehyde) through the cross-hydroxyaldehyde condensation method with benzaldehyde substituted by a benzene ring under the catalysis of alkaline reagent and, moreover, to test their antifungal potential against P. digitatum, the major citrus fruit rotting fungi. Multiple derivatives of cinnamaldehyde viz. 4-nitro CA, 4-chloro CA, 4-bromo CA, 4-methyl CA, 4-methoxy CA, and 2,4-dimethoxy CA were synthesized in the current study whereas the 4-methoxy CA showed highest antifungal actions for citrus fruit postharvest rotting fungi P. digitatum. Moreover, 4-methoxy CA was found to reduce the spore germination and growth by damaging the fungal cell membrane, as well as declined the levels of reducing sugars.

Isoeugenol and Hybrid Acetamides against Candida albicans Isolated from the Oral Cavity

Isougenol is a phytoconstituent found in several essential oils. Since many natural products are potent antimicrobials, the synthesis of hybrid molecules-combining the chemical skeleton of the phytochemical with synthetic groups-can generate substances with enhanced biological activity. Based on this, the objective of this study was to evaluate the antifungal activity of isoeugenol and hybrid acetamides against Candida albicans isolated from the oral cavity. The methodologies used were the determination of minimum inhibitory concentration (MIC), minimum fungicidal concentration (MFC), action on fungal micromorphology, interaction test with nystatin by the checkerboard method and molecular docking study with important enzymes in the maintenance of fungal viability. The synthetic molecules did not demonstrate significant antifungal activity in vitro. The isoeugenol MIC and MFC varied between 128 and 256 µg/mL, being the phytoconstituent able to interfere in the formation of blastoconid and chlamydoconid structures, important in the pathogenic process of the species. The molecular docking study revealed that isoeugenol is a potential inhibitor of the enzymes 14-α-demethylase and delta-14-sterol reductase, interfering in the fungal cell membrane biosynthesis. Thus, this research provides clearer expectations for future pharmacological studies with isoeugenol and derived molecules, aiming at its therapeutic application against infections caused by Candida spp.

A review of cinnamaldehyde and its derivatives as antibacterial agents

There is a continuing rise in the occurrence of multidrug-resistant bacterial infections. Antibiotic resistance to currently available antibiotics has become a global health issue leading to an urgent need for alternative antibacterial strategies. There has been a renewed interest in the development of antibacterial agents from natural sources, and trans-cinnamaldehyde is an example of a naturally occurring compound that has received significant attention in recent years. Trans-Cinnamaldehyde has been shown to possess substantial antimicrobial activity, as well as an array of other medicinal properties, and represents an intriguing hit compound from which a number of derivatives have been developed. In some cases, these derivatives have been shown to possess improved activity, not only compared to trans-cinnamaldehyde but also to commonly used antibiotics. Therefore, understanding the antibacterial mechanisms of action that these compounds elicit is imperative in order to facilitate their development and the development of new antibacterial agents that could exploit similar mechanistic approaches. The purpose of this review is to provide an overview of current knowledge on the antibacterial activity and mechanisms of action of cinnamaldehyde and its derivatives, and to highlight significant contributions made in this research area. It is hoped that the findings presented in this work will aid the future development of new antibacterial agents.

Antifungal Properties of Two Volatile Organic Compounds on Barley Pathogens and Introduction to Their Mechanism of Action

This study evaluated the antifungal effects of various volatile organic compounds (VOCs) against two common pathogens: Fusarium culmorum and Cochliobolus sativus. Among the various VOCs, methyl propanoate (MP) and methyl prop-2-enoate (MA) exhibited remarkable antifungal effects under different experimental conditions (direct or indirect contact) and at different concentrations (500–1000 μM). In addition, the type of antifungal effect (fungistatic or fungicidal) appeared to be strongly correlated with the VOC concentrations. Additional tests revealed that both molecules increased membrane permeability of pathogenic spores, which resulted in a decreased efflux of K⁺ ions into the intracellular medium.

Cinnamaldehyde and its derivatives, a novel class of antifungal agents

The last few decades have seen an alarming rise in fungal infections, which currently represent a global health threat. Despite extensive research towards the development of new antifungal agents, only a limited number of antifungal drugs are available in the market. The routinely used polyene agents and many azole antifungals are associated with some common side effects such as severe hepatotoxicity and nephrotoxicity. Also, antifungal resistance continues to grow and evolve and complicate patient management, despite the introduction of new antifungal agents. This suitation requires continuous attention. Cinnamaldehyde has been reported to inhibit bacteria, yeasts, and filamentous molds via the inhibition of ATPases, cell wall biosynthesis, and alteration of membrane structure and integrity. In this regard, several novel cinnamaldehyde derivatives were synthesized with the claim of potential antifungal activities. The present article describes antifungal properties of cinnamaldehyde and its derivatives against diverse classes of pathogenic fungi. This review will provide an overview of what is currently known about the primary mode of action of cinnamaldehyde. Synergistic approaches for boosting the effectiveness of cinnamaldehyde and its derivatives have been highlighted. Also, a keen analysis of the pharmacologically active systems derived from cinnamaldehyde has been discussed. Finally, efforts were made to outline the future perspectives of cinnamaldehyde-based antifungal agents. The purpose of this review is to provide an overview of current knowledge about the antifungal properties and antifungal mode of action of cinnamaldehyde and its derivatives and to identify research avenues that can facilitate implementation of cinnamaldehyde as a natural antifungal.

Thyme essential oil as a defense inducer of tomato against gray mold and Fusarium wilt

The potential of thyme essential oil in controlling gray mold and Fusarium wilt and inducing systemic acquired resistance in tomato seedlings and tomato grown in hydroponic system was evaluated. Thyme oil highly reduced 64% of Botrytis cinerea colonization on pretreated detached leaves compared to untreated control. Also, it played a significant decrease in Fusarium wilt severity especially at7 days post treatment when it was reduced to 30.76%. To explore the plant pathways triggered in response to thyme oil, phenolic compounds accumulation and peroxidase activity was investigated. Plant response was observed either after foliar spray or root feeding in hydroponics which was mostly attributed to peroxidases accumulation rather than phenolic compounds accumulation, and thyme oil seems to be more effective when applied to the roots.

Isoeugenol has a non-disruptive detergent-like mechanism of action

Isoeugenol is an essential oil constituent of nutmeg, clove, and cinnamon. Despite isoeugenol's promising antimicrobial activity, no studies have yet investigated its mode of antibacterial action at the molecular level. The aim of this study is to clarify isoeugenol's antibacterial mode of action using the Gram-negative and Gram-positive model organisms Escherichia coli and Listeria innocua, respectively. We determined the antimicrobial activity of isoeugenol against the model organisms, and examined how isoeugenol affects cell morphology, cell membrane permeabilization, and how isoeugenol interacts with phospholipid membranes using vesicle and supported lipid bilayer models. Isoeugenol demonstrated a bactericidal activity against E. coli and L. innocua that did not affect cell morphology, although the cell membrane was permeabilized. We hypothesized that the cell membrane was the primary site of action, and studied this interaction in further detail using purified membrane model systems. Isoeugenol's permeabilization of calcein-encapsulated vesicles was concentration dependent, and isoeugenol's interaction with giant unilamellar vesicles indicated increased membrane fluidity and a non-disruptive permeabilization mechanism. This contradicted membrane fluidity measurements on supported lipid bilayers (SLBs), which indicated decreased membrane fluidity. However, further investigations demonstrated that the interaction between isoeugenol and bilayers was reversible, and caused membranes to display heterogeneous topography, an increased mass, and a higher degree of hydration. In conclusion, we propose that isoeugenol interacts with membranes in a reversible non-disruptive detergent-like manner, which causes membrane destabilization. Furthermore, we argue that isoeugenol increases membrane fluidity. Our work contributes to the understanding of how essential oil constituents interact with cell components.