Antifungal Activity of Thapsia villosa Essential Oil against Candida, Cryptococcus, Malassezia, Aspergillus and Dermatophyte Species

Unveiling the mechanism of essential oil action against skin pathogens: from ancient wisdom to modern science

Essential oils are among the most well-known phyto-compounds, and since ancient times, they have been utilized in medicine. Over 100 essential oils have been identified and utilized as therapies for various skin infections and related ailments. While numerous commercial medicines are available in different dosage forms to treat skin diseases, the persisting issues include their side effects, toxicity, and low efficacy. As a result, researchers are seeking novel classes of compounds as substitutes for synthetic drugs, aiming for minimal side effects, no toxicity, and high efficacy. Essential oils have shown promising antimicrobial activity against skin-associated pathogens. This review presents essential knowledge and scientific information regarding essential oil's antimicrobial capabilities against microorganisms that cause skin infections. Essential oils mechanisms against different pathogens have also been explored. Many essential oils exhibit promising activity against various microbes, which has been qualitatively assessed using the agar disc diffusion experiment, followed by determining the minimum inhibitory concentration for quantitative evaluation. It has been observed that Staphylococcus aureus and Candida albicans have been extensively researched in the context of skin-related infections and their antimicrobial activity, including established modes of action. In contrast, other skin pathogens such as Staphylococcus epidermidis, Streptococcus pyogens, Propionibacterium acnes, and Malassezia furfur have received less attention or neglected. This review report provides an updated understanding of the mechanisms of action of various essential oils with antimicrobial properties. This review explores the anti-infectious activity and mode of action of essential against distinct skin pathogens. Such knowledge can be valuable in treating skin infections and related ailments.

Synergistic Interaction of Certain Essential Oils and Their Active Compounds with Fluconazole against Azole-resistant Strains of Cryptococcus neoformans

OBJECTIVES

This study investigated the anti-cryptococcal potential of certain essential oils (EOs)/compounds alone and in combination with fluconazole.

MATERIALS AND METHODS

We investigated the antifungal activity of oils of Cinnamomum verum, Cymbopogon citratus, Cymbopogon martini, and Syzygium aromaticum, and their major active ingredients cinnamaldehyde, citral, eugenol, and geraniol against clinical and standard strains of Cryptococcus neoformans (CN). Disc diffusion, broth microdilution, checkerboard methods, and transmission electron microscopy were employed to determine growth inhibition, synergistic interaction, and mechanism of action of test compounds.

RESULTS

EOs/compounds showed pronounced antifungal efficacy against azole-resistant CN in the order of cinnamaldehyde > eugenol > S. aromaticum > C. verum > citral > C. citratus > geraniol ≥ C. martini, each exhibiting zone of inhibition >15 mm. These oils/compounds were highly cidal compared to fluconazole. Eugenol and cinnamaldehyde showed the strongest synergy with fluconazole against CN by lowering their MICs up to 32-fold. Transmission electron microscopy indicated damage of the fungal cell wall, cell membrane, and other endomembranous organelles.

CONCLUSION

Test oils and their active compounds exhibited potential anti-cryptococcus activity against the azole-resistant strains of CN. Moreover, eugenol and cinnamaldehyde significantly potentiated the anti-cryptococcal activity of fluconazole. It is suggested that multiple sites of action from oils/compounds could turn static fluconazole into a cidal drug combination in combating cryptococcosis.

Anti-Infection of Oral Microorganisms from Herbal Medicine of Piper crocatum Ruiz & Pav

The WHO Global Status Report on Oral Health 2022 reveals that oral diseases caused by infection with oral pathogenic microorganisms affect nearly 3.5 billion people worldwide. Oral health problems are caused by the presence of S. mutans, S. sanguinis, E. faecalis and C. albicans in the oral cavity. Synthetic anti-infective drugs have been widely used to treat oral infections, but have been reported to cause side effects and resistance. Various strategies have been implemented to overcome this problem. Synthetic anti-infective drugs have been widely used to treat oral infections, but they have been reported to cause side effects and resistance. Therefore, it is important to look for safe anti-infective alternatives. Ethnobotanical and ethnopharmacological studies suggest that Red Betel leaf (Piper crocatum Ruiz & Pav) could be a potential source of oral anti-infectives. This review aims to discuss the pathogenesis mechanism of several microorganisms that play an important role in causing health problems, the mechanism of action of synthetic oral anti-infective drugs in inhibiting microbial growth in the oral cavity, and the potential of red betel leaf (Piper crocatum Ruiz & Pav) as an herbal oral anti-infective drug. This study emphasises the importance of researching natural components as an alternative treatment for oral infections that is more effective and can meet global needs.

In vitro efficacy of essential oils against various Candida species

Candida species are responsible for the most common fungal infections worldwide. We studied the in vitro antifungal activity of a large panel of essential oils (EOs) against various Candida species. The EOs activity against Candida spp. was tested using a gradient microdilution assay ranging from 4% to 0.008% (v/v). After a preliminary screening including 31 EOs, seven selected EOs were tested against 13 clinical isolates and four reference strains belonging to six Candida species. Cinnamomum zeylanicum and Cymbopogon giganteus EOs exhibited the best antifungal activity against all clinical and reference strains, with MIC ranges of 0.015%-0.25% (v/v). EOs from Litsea citrata, Backhousia citriodora and Ocimum sanctum presented MIC ranges of 0.03%-0.5% (v/v). The antifungal efficacy of EOs was independent of the susceptibility of Candida strains to usual antifungal agents. These EOs could have a promising antifungal action.

Comparative transcriptomic insights into the domestication of Pleurotus abieticola for coniferous cultivation

Introduction: Pleurotus abieticola, a promising edible fungus in the Pleurotaceae family, especially its ability to utilize coniferous substrate, holds significant potential for commercial cultivation. However, few reports on the adaptation of P. abieticola to coniferous substrate from the perspective of omics. Methods: This study explores the biological characteristics, domestication process, and nutritional composition of P. abieticola, along with its adaptability to coniferous substrates using transcriptomics. We assessed biological characteristics, optimizing mycelial growth on agar medium with varied carbon and nitrogen sources, temperature, and pH. Additionally, the optimization process extended to fruiting bodies, where impact on the differentiation were evaluated under varying light conditions. Fruiting body nutrient composition was analyzed per the Chinese National Food Safety Standard. Transcriptome sequencing focused on P. abieticola mycelial colonized coniferous and broadleaved substrates. Results and Discussion: The optimal conditions for mycelial growth were identified: dextrin (carbon source), diammonium hydrogen phosphate (nitrogen source), 25°C (temperature), and pH 7.0. White light promoted fruiting body growth and differentiation. Larch substrate exhibited superior yield (190 g) and biological efficiency (38.0%) compared to oak (131 g, 26.2%) and spruce (166 g, 33.2%). P. abieticola showcased high dietary fiber, protein, and total sugar content, low fat, and sufficient microelements. Transcriptome analysis revealed significant key genes involved in lignocellulose degradation, stress-resistant metabolism, and endocytosis metabolism, underscoring their pivotal for coniferous adaptation. This study offers valuable insights for the commercial development and strain breeding of P. abieticola, efficiently leveraging conifer resources. The findings underscore its potential as a valuable source for food, medicinal products, and biotechnological applications.

The significance of essential oils and their antifungal properties in the food industry: A systematic review

Essential oils (EOs) are natural products called volatile oils or aromatic and ethereal oils derived from various parts of plants. They possess antioxidant and antimicrobial properties, which offer natural protection against a variety of pathogens and spoilage microorganisms. Studies conducted in the last decade have demonstrated the unique applications of these compounds in the fields of the food industry, agriculture, and skin health. This systematic article provides a summary of recent data pertaining to the effectiveness of EOs and their constituents in combating fungal pathogens through diverse mechanisms. Antifungal investigations involving EOs were conducted on multiple academic platforms, including Google Scholar, Science Direct, Elsevier, Springer, Scopus, and PubMed, spanning from April 2000 to October 2023. Various combinations of keywords, such as "essential oil," "volatile oils," "antifungal," and "Aspergillus species," were used in the search. Numerous essential oils have demonstrated both in vitro and in vivo antifungal activity against different species of Aspergillus, including A. niger, A. flavus, A. parasiticus, A. fumigatus, and A. ochraceus. They have also exhibited efficacy against other fungal species, such as Penicillium species, Cladosporium, and Alternaria. The findings of this study offer novel insights into inhibitory pathways and suggest the potential of essential oils as promising agents with antifungal and anti-mycotoxigenic properties. These properties could make them viable alternatives to conventional preservatives, thereby enhancing the shelf life of various food products.

Anti-Malassezia Drug Candidates Based on Virulence Factors of Malassezia-Associated Diseases

Malassezia is a lipophilic unicellular fungus that is able, under specific conditions, to cause severe cutaneous and systemic diseases in predisposed subjects. This review is divided into two complementary parts. The first one discusses how virulence factors contribute to Malassezia pathogenesis that triggers skin diseases. These virulence factors include Malassezia cell wall resistance, lipases, phospholipases, acid sphingomyelinases, melanin, reactive oxygen species (ROS), indoles, hyphae formation, hydrophobicity, and biofilm formation. The second section describes active compounds directed specifically against identified virulence factors. Among the strategies for controlling Malassezia spread, this review discusses the development of aryl hydrocarbon receptor (AhR) antagonists, inhibition of secreted lipase, and fighting biofilms. Overall, this review offers an updated compilation of Malassezia species, including their virulence factors, potential therapeutic targets, and strategies for controlling their spread. It also provides an update on the most active compounds used to control Malassezia species.

In vitro and Quantitative and Structure Activity Relationship (QSAR) evaluation of the antifungal activity of terpenoid constituents of essential oils against Alternaria alternata and Fusarium oxysporum

INTRODUCTION

Fungal genera Alternaria and Fusarium include human and plant pathogenic species. Several antifungals have been used for their control, but excessive use has contributed to resistance development in pathogens. An alternative to searching for and developing new antifungal agents is using essential oils and their main components, which have biological activities of interest in medicine and food production.

OBJECTIVE

To evaluate in vitro and in silico the antifungal activities of terpenoids against Alternaria alternata and Fusarium oxysporum.

MATERIALS AND METHODS

The minimum inhibitory concentration and minimum fungicidal concentration values of 27 constituents of essential oils used against Alternaria alternata and Fusarium oxysporum were evaluated in vitro. In addition, using genetic algorithms, quantitative models of the structure-activity relationship were used to identify the structural and physicochemical properties related to antifungal activity.

RESULTS

The evaluated compounds proved to be effective antifungals. Thymol was the most active with a minimum inhibitory concentration of 91.6 ± 28.8 μg/ml for A. alternata and F. oxysporum. Quantitative structure-activity relationship models revealed the octanolwater cleavage ratio as the molecular property, and the phenols as the main functional group contributing to antifungal activity.

CONCLUSION

Terpenoids exhibit relevant antifungal activities that should be incorporated into the study of medicinal chemistry. Inclusion of in silico assays in the in vitro evaluation is a valuable tool in the search for and rational design of terpene derivatives as new potential antifungal agents.

Recent advances in the combinations of plant-sourced natural products for the prevention of mycotoxin contamination in food

Mycotoxins, secondary metabolites produced by mycotoxigenic fungi, are a major problem affecting food safety and security, because of their adverse health effects, their socio-economic impact and the difficulty of degradation or removal by conventional food processing methods. Plant-sourced natural products are a novel and effective control method for fungal infestation and mycotoxin production, with the advantages of biodegradability and acceptability for food use. However, development of resistance, low and inconsistent efficacy, and a limited range of antifungal activities hinder the effective application of single plant natural products for controlling mycotoxin contamination. To overcome these limitations, combinations of plant natural products have been tested extensively and found to increase efficacy, often synergistically. However, this extensive and promising research area has seen little development of practical applications. This review aims to provide up-to-date information on the antifungal, anti-mycotoxigenic and synergistic effects of combinations of plant natural products, as well as their mechanisms of action, to provide a reference source for future research and encourage application development.

The potential role of plant secondary metabolites on antifungal and immunomodulatory effect

With the widespread use of antibiotic drugs worldwide and the global increase in the number of immunodeficient patients, fungal infections have become a serious threat to global public health security. Moreover, the evolution of fungal resistance to existing antifungal drugs is on the rise. To address these issues, the development of new antifungal drugs or fungal inhibitors needs to be targeted urgently. Plant secondary metabolites are characterized by a wide variety of chemical structures, low price, high availability, high antimicrobial activity, and few side effects. Therefore, plant secondary metabolites may be important resources for the identification and development of novel antifungal drugs. However, there are few studies to summarize those contents. In this review, the antifungal modes of action of plant secondary metabolites toward different types of fungi and fungal infections are covered, as well as highlighting immunomodulatory effects on the human body. This review of the literature should lay the foundation for research into new antifungal drugs and the discovery of new targets. KEY POINTS: • Immunocompromised patients who are infected the drug-resistant fungi are increasing. • Plant secondary metabolites toward various fungal targets are covered. • Plant secondary metabolites with immunomodulatory effect are verified in vivo.

Chemical Composition and Insecticidal Activity against Tribolium Castaneum of Thapsia garganica L. Seed Essential Oil

Due to the several side effects of synthetic pesticides, including environmental pollution, threats to human health, and the development of pest resistance to insecticides, the use of alternative healthy, available and efficient agents in pest management strategies is necessary. Recently, the use of essential oil obtained from aromatic plants has shown significant potential for insect pest management. For this reason, the essential oil isolated from seeds of Thapsia garganica L. was investigated for the first time for its chemical profile, and its toxicity and repellency effects against Tribolium castaneum adults. Qualitative and quantitative analyses of the chemical composition by gas chromatography coupled to mass spectrometry (GC/MS) revealed the presence of 18 organic volatiles representing 96.8 % of the total constituents. The main compounds were 1,4-dimethylazulene (51.3 %) followed by methyl palmitate (8.2 %), methyl linoleate (6.2 %) and costol (5.1 %). Concerning the repellent effect, results revealed that SEO (Seed Essential Oil) was very repellent towards T. castaneum adults, with 100 % repellency after 2 h of exposure. Furthermore, the essential oil exhibited remarkable contact toxicity against T. castaneum (93.3 % of mortality) at the concentration of 10 % (v/v). The median lethal dose (LD50 ) of the topical application of the seed essential oil was 4.4 %. These encouraging outcomes suggested that the essential oil from T. garganica seeds could be considered a potent natural alternative to residual persistent and toxic insecticides.

Antimicrobial Activity of Some Medicinal Herbs to the Treatment of Cutaneous and Mucocutaneous Infections: Preliminary Research

(1) Background: Superficial, including cutaneous and mucocutaneous infections are a current public health problem with universal distribution. One of the main concerns, in the present/future, is fungal/bacterial infections by resistant microorganisms. This study aimed to verify if decoctions of coptidis (Coptis chinensis, Ranunculaceae family), neem (Azadirachta indica, Meliaceae family), and their essential oils (EOs), as well as the EO of manuka (Leptospermum scoparium, Myrtaceae family) have antimicrobial activity against prevalent species of microorganisms responsible for superficial infections. (2) Methods: The antimicrobial activity was determined by the minimum inhibitory concentration (MIC), using broth microdilution method, and minimum lethal concentration (MLC) was determined from subculture of MIC plates. (3) Results: C. chinensis EO and decoction demonstrated some antifungal action against the yeasts and dermatophytes tested. Greatest bactericidal effect against Propionibacterium acnes and some action against Staphylococcus aureus was observed. For A. indica only EO proved activity against dermatophytes and P. acnes. L. scoparium EO showed the broadest antimicrobial spectrum with activity against bacteria, yeasts, and dermatophytes showing greater activity against P. acnes and S. aureus. (4) Conclusions: C. chinensis (EO/decoction), EOs of L. scoparium and A. indica proved in vitro efficacy against fungal, bacterial, or mixed agents of superficial infections, either by sensitive or resistant strains.

Interactions between Natural Products-A Review

Plant-based natural products have been used as a source for therapeutics since the dawn of civilization. According to the World Health Organization (WHO), more than 80% of the world's population relies on traditional medicine for their primary healthcare. Numerous natural extracts, widely known in Traditional Chinese Medicine, Indian Ayurveda medicine and other practices, have led to the modern discovery and development of new drugs. Plants continuously interact with their environment, producing new compounds and ever-changing combinations of existing ones. Interestingly, some of the compounds have shown lower therapeutic activity in comparison to the extract they were isolated from. These findings suggest that the higher therapeutic activity of the source extract was due to the synergistic effect of several compounds. In other words, the total therapeutic potential of the extract cannot be explained only by the sum of its parts alone. In traditional medicine, most herbal remedies are based on a mixture of plants, and it is the interaction between different constituents that amplifies their therapeutic potential. Considering the significant influence traditional medicine has on human healthcare, knowing and studying the synergistic effect of compounds is paramount in designing smart therapeutic agents.

Herbal Therapy for the Treatment of Seborrhea Dermatitis

Seborrhea dermatitis is a skin disorder that usually appears on parts of the body that have high density of sebaceous glands, such as the face, chest, and scalp. Clinical manifestations that generally appear as scaly skin and erythema. Seborrhea dermatitis is also known as one of the causes of alopecia. Treatments that can be used for seborrhea dermatitis are antifungal, anti-inflammatory, keratolytic, and coal tar. There are concerns about poor adherence, resistance, and some side effects of drugs that have been used in the treatment of seborrhea dermatitis. Concerns regarding these issues increase the urgency for the development of new therapeutic agents in the treatment of seborrhea dermatitis. Research on medicinal plants has enormous potential to produce compounds with new structures and bioactivity. This review discusses clinical and in vitro studies related to the activity of several medicinal plants that have potential as a treatment for seborrhea dermatitis, as well as the compounds that play a role in these activities. Literature searches were carried out on the PubMed, Taylor & Francis, and SpringerLink databases using Boolean Operators to get 25 articles that match the keywords used. Of the 25 articles, six were clinical trials, while 19 were in vitro studies of Malassezia. Several plants have potential as promising therapeutic agents for the treatment of seborrhea dermatitis by inhibiting the growth of Malassezia, decreasing sebum secretion, and decreasing symptoms associated with seborrhea dermatitis such as itching, pain or burning sensation, and redness.

Identification of Novel and Safe Fungicidal Molecules against Fusarium oxysporum from Plant Essential Oils: In Vitro and Computational Approaches

Phytopathogenic fungi are serious threats in the agriculture sector especially in fruit and vegetable production. The use of plant essential oil as antifungal agents has been in practice from many years. Plant essential oils (PEOs) of Cuminum cyminum, Trachyspermum ammi, Azadirachta indica, Syzygium aromaticum, Moringa oleifera, Mentha spicata, Eucalyptus grandis, Allium sativum, and Citrus sinensis were tested against Fusarium oxysporum. Three phase trials consist of lab testing (MIC and MFC), field testing (seed treatment and foliar spray), and computer-aided fungicide design (CAFD). Two concentrations (25 and 50 μl/ml) have been used to asses MIC while MFC was assessed at four concentrations (25, 50, 75, and 100 μl/ml). C. sinensis showed the largest inhibition zone (47.5 and 46.3 m2) for both concentrations. The lowest disease incidence and disease severity were recorded in treatments with C. sinensis PEO. Citrus sinensis that qualified in laboratory and field trials was selected for CAFD. The chemical compounds of C. sinensis PEO were docked with polyketide synthase beta-ketoacyl synthase domain of F. oxysporum by AutoDock Vina. The best docked complex was formed by nootkatone with -6.0 kcal/mol binding affinity. Pharmacophore of the top seven C. sinensis PEO compounds was used for merged pharmacophore generation. The best pharmacophore model with 0.8492 score was screened against the CMNP database. Top hit compounds from screening were selected and docked with polyketide synthase beta-ketoacyl synthase domain. Four compounds with the highest binding affinity and hydrogen bonding were selected for confirmation of lead molecule by doing MD simulation. The polyketide synthase-CMNPD24498 showed the highest stability throughout 80 ns run of MD simulation. CMNPD24498 (FW054-1) from Verrucosispora was selected as the lead compound against F. oxysporum.

Antifungal Activity of Select Essential Oils against Candida auris and Their Interactions with Antifungal Drugs

Candida auris is an emerging fungal pathogen that commonly causes nosocomial blood infections in the immunocompromised. Several factors make this pathogen a global threat, including its misidentification as closely related species, its ability to survive for weeks on fomites, and its resistance to commonly prescribed antifungal drugs, sometimes to all three classes of systemic antifungal drugs. These factors demonstrate a need for the development of novel therapeutic approaches to combat this pathogen. In the present study, the antifungal activities of 21 essential oils were tested against C. auris. Several essential oils were observed to inhibit the growth and kill C. auris, Candida lusitaniae, and Saccharomyces cerevisiae when in direct contact and at concentrations considered safe for topical use. The most effective essential oils were those extracted from lemongrass, clove bud, and cinnamon bark. These essential oils also elicited antifungal activity in gaseous form. The efficacies of formulations comprised of these three essential oils in combination with fluconazole, amphotericin B, flucytosine, and micafungin were explored. While synergism was neither observed with cinnamon bark oil nor any of the antifungal drugs, lemongrass oil displayed synergistic, additive, and indifferent interactions with select drugs. Formulations of clove bud oil with amphotericin B resulted in antagonistic interactions but displayed synergistic interactions with fluconazole and flucytosine. These essential oils and their combinations with antifungal drugs may provide useful options for surface disinfection, skin sanitization, and possibly even the treatment of Candida infections.

Essential Oils in Respiratory Mycosis: A Review

Respiratory mycosis is a major health concern, due to the expanding population of immunosuppressed and immunocompromised patients and the increasing resistance to conventional antifungals and their undesired side-effects, thus justifying the development of new therapeutic strategies. Plant metabolites, namely essential oils, represent promising preventive/therapeutic strategies due to their widely reported antifungal potential. However, regarding fungal infections of the respiratory tract, information is disperse and no updated compilation on current knowledge is available. Therefore, the present review aims to gather and systematize relevant information on the antifungal effects of several essential oils and volatile compounds against the main type of respiratory mycosis that impact health care systems. Particular attention is paid to Aspergillus fumigatus, the main pathogen involved in aspergillosis, Candida auris, currently emerging as a major pathogen in certain parts of the world, and Cryptococcus neoformans, one of the main pathogens involved in pulmonary cryptococcosis. Furthermore, the main mechanisms of action underlying essential oils’ antifungal effects and current limitations in clinical translation are presented. Overall, essential oils rich in phenolic compounds seem to be very effective but clinical translation requires more comprehensive in vivo studies and human trials to assess the efficacy and tolerability of these compounds in respiratory mycosis.

Apiaceae Essential Oils: Boosters of Terbinafine Activity against Dermatophytes and Potent Anti-Inflammatory Effectors

Dermatophyte infections represent an important public health concern, affecting up to 25% of the world's population. Trichophyton rubrum and T. mentagrophytes are the predominant dermatophytes in cutaneous infections, with a prevalence accounting for 70% of dermatophytoses. Although terbinafine represents the preferred treatment, its clinical use is hampered by side effects, drug-drug interactions, and the emergence of resistant clinical isolates. Combination therapy, associating terbinafine and essential oils (EOs), represents a promising strategy in the treatment of dermatophytosis. In this study, we screened the potential of selected Apiaceae EOs (ajowan, coriander, caraway, and anise) to improve the antifungal activity of terbinafine against T. rubrum ATCC 28188 and T. mentagrophytes ATCC 9533. The chemical profile of EOs was analyzed by gas chromatography. The minimal inhibitory concentration (MIC) and minimal fungicidal concentration (MFC) of EOs/main compounds were determined according to EUCAST-AFST guidelines, with minor modifications. The checkerboard microtiter method was used to identify putative synergistic combinations of EOs/main constituents with terbinafine. The influence of EOs on the viability and pro-inflammatory cytokine production (IL-1β, IL-8 and TNF-α) was determined using an ex vivo human neutrophils model. The binary associations of tested EOs with terbinafine were found to be synergistic against T. rubrum, with FICI values of 0.26-0.31. At the tested concentrations (6.25-25 mg/L), EOs did not exert cytotoxic effects towards human neutrophils. Anise EO was the most potent inhibitor of IL-1β release (46.49% inhibition at 25 mg/L), while coriander EO displayed the highest inhibition towards IL-8 and TNF-α production (54.15% and 54.91%, respectively). In conclusion, the synergistic combinations of terbinafine and investigated Apiaceae EOs could be a starting point in the development of novel topical therapies against T. rubrum-related dermatophytosis.

Using essential oils from Citrus paradisi as a fumigant for Solenopsis invicta workers and evaluating the oils' effect on worker behavior

The red imported fire ant is one of the world's most devastating invasive species, adversely affecting humans, wildlife, crops, and livestock. To control infestations, chemical pesticides are deployed extensively around the world. However, their extensive use has led to negative effects on the environment and human health. Essential oils, which are safe and ecofriendly, can potentially be used as alternatives to chemical pesticides. In this study, grapefruit essential oils were used as fumigant agents to control red imported fire ants. The crude grapefruit oil (GO1) contained 28 compounds, and the concentrated grapefruit oil (GO2), which was refined from GO1 by vacuum distillation, contained 20 compounds. D-Limonene was the dominant constituent in both GO1 (70.1%) and GO2 (73.96%), and other important constituents included β-pinene, α-pinene, β-phellandrene, octanal, d-carvone, α-terpineol, and linalool. Both the essential oils and their individual constituents (α-pinene, α-terpineol, β-phellandrene, octanal, and d-carvone) showed strong lethal fumigant effects against workers. Workers were more susceptible to GO2 than GO1, and octanal was more toxic to workers as compared with the other four constituents. When antennas of workers were treated with the two oils or the five constituents, their walking and gripping abilities were significantly suppressed, and there was an obvious bending or breaking phenomenon on the sensilla of the antennas. Fumigant activity by grapefruit essential oils and their main compounds were associated with their effects on the walking and gripping behavior of workers, and this confirmed that grapefruit essential oil is a promising, ecofriendly, and safe fumigant for the control of red imported fire ants.

Conventional therapy and new antifungal drugs against Malassezia infections

Malassezia yeasts are commensal microorganisms occurring on the skin of humans and animals causing dermatological disorders or systemic infections in severely immunocompromised hosts. Despite attempts to control such yeast infections with topical and systemic antifungals, recurrence of clinical signs of skin infections as well as treatment failure in preventing or treating Malassezia furfur fungemia have been reported most likely due to wrong management of these infections (e.g., due to early termination of treatment) or due to the occurrence of resistant phenomena. Standardized methods for in vitro antifungal susceptibility tests of these yeasts are still lacking, thus resulting in variable susceptibility profiles to azoles among Malassezia spp. and a lack of clinical breakpoints. The inherent limitations to the current pharmacological treatments for Malassezia infections both in humans and animals, stimulated the interest of the scientific community to discover new, effective antifungal drugs or substances to treat these infections. In this review, data about the in vivo and in vitro antifungal activity of the most commonly employed drugs (i.e., azoles, polyenes, allylamines, and echinocandins) against Malassezia yeasts, with a focus on human bloodstream infections, are summarized and their clinical implications are discussed. In addition, the usefulness of alternative compounds is discussed.

Essential oils as Potential Source of Anti-dandruff Agents: A Review

BACKGROUND

Dandruff is a frequently occurring scalp problem that causes significant discomfort to approximately 50% population at some stage of life, especially post-puberty and pre-adult age.

OBJECTIVE

This review aims to summarize the recent findings regarding the anti-fungal properties of herbal essential oils against pathogens involved in dandruff prognosis.

METHODS

A literature search of studies published between 2000 and 2020 was conducted over databases: PubMed, Google Scholar, Scopus, and Science direct. Literature was explored using the guidelines given in Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA).

RESULTS

Dandruff, characterized by clinical symptoms of dryness, pruritis, scaly, and flaky scalp, is considered a pri-mary manifestation of seborrheic dermatitis. Amongst various etiological and pathophysiological factors, a significant role of yeasts, primarily species of Malassezia, Candida, has been strongly correlated with dandruff. At the same time, incidences of M. furfur, M. restricta, and M. globosa are high compared to others. Due to relapse of symptoms with the withdrawal of conventional anti-dandruff products. Essential oils of herbal origin, such as tea tree oil, lime oil, rose-mary oil, have gained global importance in dermatology. These oils are rich in secondary aromatic metabolites, espe-cially terpenes and phenolic components that impart substantial antimicrobial properties and resisting biofilm production.

CONCLUSION

Based on the available information, we can conclude that essential oils have tremendous potential to be developed as anti-dandruff products; however, further studies are warranted to establish their efficacy in dandruff cures.

Development of Microemulsion Containing Alpinia galanga Oil and Its Major Compounds: Enhancement of Antimicrobial Activities

The aim of the present study was to develop a microemulsion (ME) containing Alpinia galanga oil (AGO), 1,8-cineole (C), or methyl eugenol (M) as an active pharmaceutical ingredient (API) for enhancing their antimicrobial activities. Agar diffusion, broth microdilution, and killing kinetics were used for antimicrobial evaluations. The ME composed of 30% API, 33.4% Tween 80, 16.6% ethanol, and 20% water appeared as translucent systems with droplet size and polydispersity index of 101.1 ± 1.3 nm and 0.3 ± 0.1, 80.9 ± 1.1 nm and 0.4 ± 0.1, and 96.6 ± 2.0 nm and 0.2 ± 0.1 for ME-AGO, ME-C, and ME-M, respectively. These ME formulations showed minimum bacterial concentrations of 3.91–31.25 µg/mL and 50% fungal inhibition concentrations of 1.83 ± 0.27–0.46 ± 0.13 µg/mL, 2–4 times stronger, and faster kinetic killing rate than their respective API alone. Keeping the ME formulations at 4 °C, 25 °C, and 40 °C for 12 weeks did not affect their activities against fungi and Gram-negative bacteria, but the high temperature of 40 °C decreased their activities against Gram-positive bacteria. It is concluded that ME is a promising delivery system for AGO and its major compounds to enhance their water miscibility and antimicrobial activities.

Antifungal activity of different essential oils against Malassezia pathogenic species

ETHNOPHARMACOLOGICAL RELEVANCE

Plants produce essential oils in response to physiological stresses, pathogen attacks and ecological factors. Nowadays, they are recognized as defence compounds and attractors of pollinators. Essential oils have been traditionally used in the past years in various cultures for medicinal and health purposes. In recent times due to their well-documented antimicrobial activities, essential oils have consolidated their use in raw and processed food preservation, health and clinical uses.

AIMS OF THE REVIEW

The potential activity of essential oils against the largely diffused Malassezia species on the human skin, which can cause common infections or exacerbate multiple skin disorders, such as P. versicolor, folliculitis, seborrheic dermatitis and dandruff, atopic dermatitis and psoriasis.

MATERIALS AND METHODS

Information on essential oils activity against Malassezia species was obtained from published materials, including books and electronic databases, such as SCI finder, PubMed, Web of Science, ACS, Science Direct, Wiley, Springer, Taylor, J-STAGE and Google Scholar. Search was conducted covering the period from January 2013 to December 2018.

RESULTS

In the in vitro studies diverse methods were used to test the essential oils activity, namely broth microdilution method, which resulted the most used one, followed by agar disk diffusion and vapour phase methods. Essential oils obtained by steam distillation were from different plant genera, Thymus, Artemisia, Malaleuca, Cinnamomun, Ocimum, Zataria, Rosmarinus, Origanum, Syzigium, Foenicolum, Thapsia, Tachyspermum, Myrtus. MIC values were expressed as μg/mL, μL/mL and by inhibition zone (mm) or μL/cm³. All the investigated essential oils were active at the tested conditions. In addition, two clinical studies used essential oils from Cymbopogon citratus and C. flexuosus formulated in shampoo, cream or lotion for the successful treatment of dandruff and P. versicolor.

CONCLUSIONS

Results of these studies indicate worthy prospects for clinical application of essential oils and there is an urgent need to conduct further in vivo studies with large number of patients in order to verify the clinical potential of essential oils against Malassezia species.

Lipid composition and cell surface hydrophobicity of Candida albicans influence the efficacy of fluconazole-gentamicin treatment

Adherence of the fungus, Candida albicans, to biotic (e.g. human tissues) and abiotic (e.g. catheters) surfaces can lead to emergence of opportunistic infections in humans. The process of adhesion and further biofilm development depends, in part, on cell surface hydrophobicity (CSH). In this study, we compared the resistance of C. albicans strains with different CSH to the most commonly prescribed antifungal drug, fluconazole, and the newly described synergistic combination, fluconazole and gentamicin. The hydrophobic strain was more resistant to fluconazole due to, among others, overexpression of the ERG11 gene encoding the fluconazole target protein (CYP51A1, Erg11p), which leads to overproduction of ergosterol in this strain. Additionally, the hydrophobic strain displayed high efflux activity of the multidrug resistance Cdr1 pump due to high expression of the CDR1 gene. On the other hand, the hydrophobic C. albicans strain was more susceptible to fluconazole-gentamicin combination because of its different effect on lipid content in the two strains. The combination resulted in ergosterol depletion with subsequent Cdr1p mislocalization and loss of activity in the hydrophobic strain. We propose that C. albicans strains with different CSH may possess altered lipid metabolism and consequently may differ in their response to treatment.

Bigger Data Approach to Analysis of Essential Oils and Their Antifungal Activity against Aspergillus niger, Candida albicans, and Cryptococcus neoformans

With increasing drug resistance and the poor state of current antifungals, the need for new antifungals is urgent and growing. Therefore, we tested a variety of essential oils for antifungal activity. We report the minimum inhibitory concentrations (MIC) values for a common set of 82 essential oils against Aspergillus niger, Candida albicans, and Cryptococcus neoformans. Generally, narrow-spectrum activity was found. However, C. neoformans was much more susceptible to inhibition by essential oils with over one-third of those tested having MIC values below 160 ppm. GC-MS analysis showed the essential oils to be chemically diverse, yet, the potentially active major constituents typically fell into a few general categories (i.e., terpenes, terpenoids, terpenols). While essential oils remain a rich source of potential antifungals, focus should shift to prioritizing activity from novel compounds outside the commonalities reported here, instead of simply identifying antifungal activity. Further, capitalizing on bigger data approaches can provide significant returns in expediting the identification of active components.

Essential Oil Compositions and Antifungal Activity of Sunflower (Helianthus) Species Growing in North Alabama

Helianthus species are North American members of the Asteraceae, several of which have been used as traditional medicines by Native Americans. The aerial parts of two cultivars of Helianthus annuus, “Chianti” and “Mammoth”, and wild-growing H. strumosus, were collected from locations in north Alabama. The essential oils were obtained by hydrodistillation and analyzed by gas chromatography—mass spectrometry. The Helianthus essential oils were dominated by monoterpene hydrocarbons, in particular α-pinene (50.65%, 48.91%, and 58.65%, respectively), sabinene (6.81%, 17.01%, and 1.91%, respectively), β-pinene (5.79%, 3.27%, and 4.52%, respectively), and limonene (7.2%, 7.1%, and 3.8%, respectively). The essential oils were screened against three opportunistic pathogenic fungal species, Aspergillus niger, Candida albicans, and Cryptococcus neoformans. The most sensitive fungus was C. neoformans with minimum inhibitory concentration (MIC) values of 78, 156, and 78 μg/mL, respectively.

Antifungal activity of essential oil from Mentha spicata L. and Mentha pulegium L. growing wild in Sardinia island (Italy)

This study aims to evaluate the antifungal activity of Mentha spicata L. and Mentha pulegium L. from Sardinia and to assess their efficacy on virulence factors for Candida albicans, particularly on the inhibition of the germ tube formation. The major compounds of the essential oils were carvone (62.9%) for M. spicata and pulegone (86.2%) for M. pulegium. The essential oil from M. spicata showed a more preeminent effect against Cryptococcus neoformans and the dermatophytes Trichophyton rubrum and T. verrucosum (0.32 μL/mL). Both oils were very effective in inhibiting C. albicans germ tube formation, at doses well below their MIC (0.16 μL/mL).

Chemical characterization and antifungal activity of Origanum vulgare, Thymus vulgaris essential oils and carvacrol against Malassezia furfur

The composition of the essential oils (EOs) of O. vulgare L. EO and T. vulgaris EO, were analyzed by GC and GC-MS. Antifungal activities of the EOs and its main component, carvacrol, were evaluated against 27 clinical isolates of Malassezia furfur. Minimum inhibitory concentrations (MICs) were measured according to the broth microdilution protocols by Clinical and Laboratory Standards Institute (CLSI) modified for Malassezia spp. EOs and carvacrol showed low MIC values ranged 450-900 μg/ml against M. furfur. No differences in EOs antifungal activity were observed in sensitive to resistant fluconazole isolates. The antifungal activity obtained showed O. vulgare EO, T. vulgaris EO and carvacrol, their compound, as potential antimicrobial agents against M. furfur, yeast associated with human mycoses.