Anti-Candida albicans effectiveness of citral and investigation of mode of action

Screening and In Silico Analyses of the Yeast Saccharomyces cerevisiae Σ1278b Bank Mutants Using Citral as a Natural Antimicrobial

The antimicrobial function of citral, one of the main compounds of the essential oils (EO) of the Citrus genus, and widely used by the food industry toward spoilage yeast, was previously proven. In this study, the possible mode of action of citral against yeast cells was evaluated by using a global deletome approach. Firstly, the suitability of Saccharomyces cerevisiae Σ1278b to serve as model yeast was assessed by determining its sensitivity to citral (MIC = 0.5 μL/mL). Subsequently, the complete library of Σ1278b haploid mutants deleted in 4019 non-essential genes was screened to identify potential molecular targets of citral. Finally, the deleted genes in the 590 mutants showing increased citral resistance was analyzed with an in-silico approach (Gene Ontology). The significantly enriched GO Terms were "cytoplasm", "vacuole", and "mitochondrion" (cellular components); "catalytic activity" (molecular function); "pseudohyphal growth" (biological process). For molecular function, resistant mutants were grouped into thiosulfate sulfur transferase activity, transferase activity, and oxidoreductase activity; for cellular components, resistant mutants were grouped as: cytoplasm, intracellular organelle, membrane-bounded organelle, mitochondrion, organelle membrane, and vacuole; and finally, with regard to biological process, deleted genes were grouped as: pseudohyphal growth, mitochondrion organization, lipid metabolic process, DNA recombination and repair, and proteolysis. Interestingly, many identified genes were associated with the cellular response to oxidative stress and ROS scavenging. These findings have important implications for the development of citral-based antimicrobials and the elucidation of its mechanism of action.

ROS mediated anticandidal efficacy of 3-Bromopyruvate prevents vulvovaginal candidiasis in mice model

Candidal infections, particularly vulvovaginal candidiasis (VVC), necessitate effective therapeutic interventions in clinical settings owing to their intricate clinical nature and elusive understanding of their etiological mechanisms. Given the challenges in developing effective antifungal therapies, the strategy of repurposing existing pharmaceuticals has emerged as a promising approach to combat drug-resistant fungi. In this regard, the current study investigates molecular insights on the anti-candidal efficacy of a well-proven anticancer small molecule -3-bromopyruvate (3BP) against three clinically significant VVC causing Candida species viz., C. albicans, C. tropicalis and C. glabrata. Furthermore, the study validates 3BP's therapeutic application by developing it as a vaginal cream for the treatment of VVC. 3BP exhibited phenomenal antifungal efficacy (killing >99%) with minimum inhibitory concentrations (MIC) and minimum fungicidal concentrations (MFC) of 256 μg/mL against all tested Candida spp. Time killing kinetics experiment revealed 20 min as the minimum time required for 3BP at 2XMIC to achieve complete-killing (99.9%) in all Candida strains. Moreover, the ergosterol or sorbitol experiment explicated that the antifungal activity of 3BP does not stem from targeting the cell wall or the membrane component ergosterol. Instead, 3BP was observed to instigate a sequence of pre-apoptotic cascade events, such as phosphatidylserine (PS) externalization, nuclear condensation and ROS accumulations, as evidenced by PI, DAPI and DCFH-DA staining methods. Furthermore, 3BP demonstrated a remarkable efficacy in eradicating mature biofilms of Candida spp., achieving a maximum eradication level of 90%. Toxicity/safety profiling in both in vitro erythrocyte lysis and in vivo Galleria mellonella survival assay authenticated the non-toxic nature of 3BP up to 512 μg/mL. Finally, a vaginal cream formulated with 3BP was found to be effective in VVC-induced female mice model, as it significantly decreasing fungal load and protecting vaginal mucosa. Concomitantly, the present study serves as a clear demonstration of antifungal mechanistic action of anticancer drug -3BP, against Candida species. This finding holds significant potential for mitigating candidal infections, particularly VVC, within healthcare environments.

Clove Essential Oil and Its Main Constituent, Eugenol, as Potential Natural Antifungals against Candida spp. Alone or in Combination with Other Antimycotics Due to Synergistic Interactions

The occurrence of candidiasis, including superficial infections, has recently increased dramatically, especially in immunocompromised patients. Their treatment is often ineffective due to the resistance of yeasts to antimycotics. Therefore, there is a need to search for new antifungals. The aim of this study was to determine the antifungal effect of clove essential oil (CEO) and eugenol (EUG) towards both reference and clinical Candida spp. strains isolated from the oral cavity of patients with hematological malignancies, and to investigate their mode of action and the interactions in combination with the selected antimycotics. These studies were performed using the broth microdilution method, tests with sorbitol and ergosterol, and a checkerboard technique, respectively. The CEO and EUG showed activity against all Candida strains with a minimal inhibitory concentration (MIC) in the range of 0.25-2 mg/mL. It was also found that both natural products bind to ergosterol in the yeast cell membrane. Moreover, the interactions between CEO and EUG with several antimycotics-cetylpyridinium chloride, chlorhexidine, silver nitrate and triclosan-showed synergistic or additive effects in combination, except nystatin. This study confirms that the studied compounds appear to be a very promising group of phytopharmaceuticals used topically in the treatment of superficial candidiasis. However, this requires further studies in vivo.

Candida albicans Reactive Oxygen Species (ROS)-Dependent Lethality and ROS-Independent Hyphal and Biofilm Inhibition by Eugenol and Citral

Candida albicans is part of the normal human flora but is most frequently isolated as the causative opportunistic pathogen of candidiasis. Plant-based essential oils and their components have been extensively studied as antimicrobials, but their antimicrobial impacts are poorly understood. Phenylpropenoids and monoterpenes, for example, eugenol from clove and citral from lemon grass, are potent antifungals against a wide range of pathogens. We report the cellular response of C. albicans to eugenol and citral, alone and combined, using biochemical and microscopic assays. The MICs of eugenol and citral were 1,000 and 256 μg/mL, respectively, with the two exhibiting additive effects based on a fractional inhibitory concentration index of 0.83 ± 0.14. High concentrations of eugenol caused membrane damage, oxidative stress, vacuole segregation, microtubule dysfunction and cell cycle arrest at the G₁/S phase, and while citral had similar impacts, they were reactive oxygen species (ROS) independent. At sublethal concentrations (1/2 to 1/4 MIC), both oils disrupted microtubules and hyphal and biofilm formation in an ROS-independent manner. While both compounds disrupt the cell membrane, eugenol had a greater impact on membrane dysfunction. This study shows that eugenol and citral can induce vacuole and microtubule dysfunction, along with the inhibition of hyphal and biofilm formation. IMPORTANCE Candida albicans is a normal resident on and in the human body that can cause relatively benign infections. However, when our immune system is severely compromised (e.g., cancer chemotherapy patients) or underdeveloped (e.g., newborns), this fungus can become a deadly pathogen, infecting the bloodstream and organs. Since there are only a few effective antifungal agents that can be used to combat fungal infections, these fungi have been exposed to them over and over again, allowing the fungi to develop resistance. Instead of developing antifungal agents that kill the fungi, some of which have undesirable side effects on the human host, researchers have proposed to target the fungal traits that make the fungus more virulent. Here, we show how two components of plant-based essential oils, eugenol and citral, are effective inhibitors of C. albicans virulence traits.

Alteration of Cell Membrane Permeability by Cetyltrimethylammonium Chloride Induces Cell Death in Clinically Important Candida Species

The increased incidence of healthcare-related Candida infection has necessitated the use of effective disinfectants/antiseptics in healthcare settings as a preventive measure to decontaminate the hospital environment and stop the persistent colonization of the offending pathogens. Quanternary ammonium surfactants (QASs), with their promising antimicrobial efficacy, are considered as intriguing and appealing candidates for disinfectants. From this perspective, the present study investigated the antifungal efficacy and action mechanism of the QAS cetyltrimethylammonium chloride (CTAC) against three clinically important Candida species: C. albicans, C. tropicalis, and C. glabrata. CTAC exhibited phenomenal antifungal activity against all tested Candida spp., with minimum inhibitory concentrations (MIC) and minimum fungicidal concentrations (MFC) between 2 and 8 µg/mL. The time−kill kinetics of CTAC (at 2XMIC) demonstrated that an exposure time of 2 h was required to kill 99.9% of the inoculums in all tested strains. An important observation was that CTAC treatment did not influence intracellular reactive oxygen species (ROS), signifying that its phenomenal anticandidal efficacy was not mediated via oxidative stress. In addition, sorbitol supplementation increased CTAC’s MIC values against all tested Candida strains by three times (8−32 μg/mL), indicating that CTAC’s possible antifungal activity involves fungus cell membrane destruction. Interestingly, the increased fluorescence intensity of CTAC-treated cells in both propidium iodide (PI) and DAPI staining assays indicated the impairment of cell plasma membrane and nuclear membrane integrity by CTAC, respectively. Additionally, CTAC at MIC and 2XMIC was sufficient (>80%) to disrupt the mature biofilms of all tested spp., and it inhibited the yeast-to-hyphae transition at sub-MIC in C. albicans. Finally, the non-hemolytic activity of CTAC (upto 32 µg/mL) in human blood cells and HBECs signified its non-toxic nature at the investigated concentrations. Furthermore, thymol and citral, two phytocompounds, together with CTAC, showed synergistic fungicidal effectiveness against C. albicans planktonic cells. Altogether, the data of the present study appreciably broaden our understanding of the antifungal action mechanism of CTAC and support its future translation as a potential disinfectant against Candida-associated healthcare infections.

Recent Advances in the Application of Essential Oils as Potential Therapeutic Candidates for Candida-Related Infections

Candidiasis (oral, vulvovaginal, or systemic bloodstream infections) are important human fungal infections associated with a high global prevalence in otherwise healthy adults but are also opportunistic infections in immunocompromised patients. With the recent discovery of the multidrug resistant—and often difficult to treat—Candida auris, as well as the rising costs associated with hospitalisations and the treatment of infections caused by Candida species, there is an urgent need to develop effective therapeutics against these pathogenic yeasts. Essential oils have been documented for many years as treatments for different ailments and are widely known and utilised in alternative and complementary therapies, including treating microbial infections. This review highlights knowledge from research on the effects of medicinal plants, and in particular, essential oils, as potential treatments against different Candida species. Studies have been evaluated that describe the experimental approaches used in investigating the anticandidal effects of essential oils (in vivo and in vitro), the established mode of action of the different compounds against different Candida species, the effect of a combination of essential oils with other compounds as potential therapies, and the evidence from clinical trial studies.

In vitro and in vivo anti-Candida activity of citral in combination with fluconazole

Background

The ability of Candida to develop biofilms on inert surfaces or living tissues favors recalcitrant and chronic candidiasis associated, in many instances, with resistance to current antifungal therapy.

Aim

The aim of this study was to evaluate the antifungal activity of citral, a phytocompound present in lemongrass essential oil, in monotherapy and combined with fluconazole against azole-resistant Candida planktonic cells and biofilms. The effect of citral combined with fluconazole was also analysed with regard to the expression of fluconazole resistance-associated genes in Candida albicans and the effectiveness of the combination therapy in a Caenorhabditis elegans model of candidiasis.

Results

Citral reduced biofilm formation at initial stages and the metabolic activity of the mature biofilm. The combination of citral with fluconazole was synergistic, with a significant increase in the survival of C. elegans infected with Candida. RNA analysis revealed a reduction of the expression of the efflux pump encoded by MDR1, leading to a greater effect of fluconazole.

Conclusion

Citral in monotherapy and in combination with fluconazole could represent an interesting therapy to treat recalcitrant Candida infections associated to biofilms.

The newly synthesized thiazole derivatives as potential antifungal compounds against Candida albicans

Abstract

Recently, the occurrence of candidiasis has increased dramatically, especially in immunocompromised patients. Additionally, their treatment is often ineffective due to the resistance of yeasts to antimycotics. Therefore, there is a need to search for new antifungals. A series of nine newly synthesized thiazole derivatives containing the cyclopropane system, showing promising activity against Candida spp., has been further investigated. We decided to verify their antifungal activity towards clinical Candida albicans isolated from the oral cavity of patients with hematological malignancies and investigate the mode of action on fungal cell, the effect of combination with the selected antimycotics, toxicity to erythrocytes, and lipophilicity. These studies were performed by the broth microdilution method, test with sorbitol and ergosterol, checkerboard technique, erythrocyte lysis assay, and reversed phase thin-layer chromatography, respectively. All derivatives showed very strong activity (similar and even higher than nystatin) against all C. albicans isolates with minimal inhibitory concentration (MIC) = 0.008–7.81 µg/mL Their mechanism of action may be related to action within the fungal cell wall structure and/or within the cell membrane. The interactions between the derivatives and the selected antimycotics (nystatin, chlorhexidine, and thymol) showed additive effect only in the case of combination some of them and thymol. The erythrocyte lysis assay confirmed the low cytotoxicity of these compounds as compared to nystatin. The high lipophilicity of the derivatives was related with their high antifungal activity. The present studies confirm that the studied thiazole derivatives containing the cyclopropane system appear to be a very promising group of compounds in treatment of infections caused by C. albicans. However, this requires further studies in vivo.

Key points

• The newly thiazoles showed high antifungal activity and some of them — additive effect in combination with thymol.

• Their mode of action may be related with the influence on the structure of the fungal cell wall and/or the cell membrane.

• The low cytotoxicity against erythrocytes and high lipophilicity of these derivatives are their additional good properties.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-021-11477-7.

Citral derivative activates cell cycle arrest and apoptosis signaling pathways in Candida albicans by generating oxidative stress

For combating life-threatening infections caused by Candida albicans there is an urgent requirement of new antifungal agents with a targeted activity and low host cytotoxicity. Manipulating the mechanistic basis of cell death decision in yeast may provide an alternative approach for future antifungal therapeutics. Herein, the effect of an active citral derivative (Cd1) over the physiology of cell death in C. albicans was assessed. The viability of C. albicans SC5314 cells was determined by broth microdilution assay. The crucial morphological changes and apoptotic markers in Cd1-exposed yeast cells were analyzed. Subsequently the results confirmed that Cd1 arrested growth and caused death in yeast cells. Furthermore, this molecule inhibited antioxidant enzymes that resulted in production of reactive oxygen species. DNA fragmentation and condensation, phosphatidylserine exposure at the outer leaflet of cell membrane, mitochondrial disintegration as well as accumulation of cells at G2/M phase of the cell cycle were recorded. Altogether, this derivative induced apoptotic-type cell death in C. albicans SC5314.

Synthesis and Physicochemical Characterization of Novel Dicyclopropyl-Thiazole Compounds as Nontoxic and Promising Antifungals

There is a need to search for new antifungals, especially for the treatment of the invasive Candida infections, caused mainly by C. albicans. These infections are steadily increasing at an alarming rate, mostly among immunocompromised patients. The newly synthesized compounds (3a-3k) were characterized by physicochemical parameters and investigated for antimicrobial activity using the microdilution broth method to estimate minimal inhibitory concentration (MIC). Additionally, their antibiofilm activity and mode of action together with the effect on the membrane permeability in C. albicans were investigated. Biofilm biomass and its metabolic activity were quantitatively measured using crystal violet (CV) staining and tetrazolium salt (XTT) reduction assay. The cytotoxic effect on normal human lung fibroblasts and haemolytic effect were also evaluated. The results showed differential activity of the compounds against yeasts (MIC = 0.24-500 µg/mL) and bacteria (MIC = 125-1000 µg/mL). Most compounds possessed strong antifungal activity (MIC = 0.24-7.81 µg/mL). The compounds 3b, 3c and 3e, showed no inhibitory (at 1/2 × MIC) and eradication (at 8 × MIC) effect on C. albicans biofilm. Only slight decrease in the biofilm metabolic activity was observed for compound 3b. Moreover, the studied compounds increased the permeability of the membrane/cell wall of C. albicans and their mode of action may be related to action within the fungal cell wall structure and/or within the cell membrane. It is worth noting that the compounds had no cytotoxicity effect on pulmonary fibroblasts and erythrocytes at concentrations showing anticandidal activity. The present studies in vitro confirm that these derivatives appear to be a very promising group of antifungals for further preclinical studies.

Citral and geraniol induce necrotic and apoptotic cell death on Saccharomyces cerevisiae

Essential oils and their main components, monoterpenes, have been proven to be important alternatives for the control of pathogenic and spoiling microorganisms, but the mode of action of these compounds is poorly understood. This work aimed to determine the mode of action of citral and geraniol on the model yeast Saccharomyces cerevisiae using a flow cytometry approach. Exponentially growing yeast cells were treated with different concentrations of citral and geraniol for 3 h, and evaluated for cell wall susceptibility to glucanase, membrane integrity, reactive oxygen species (ROS) accumulation, mitochondrial membrane potential, and metacaspase activity. Results provide strong evidence that citral and geraniol acute fungicidal activity against Saccharomyces cells involves the loss of membrane and cell wall integrity resulting in a dose-dependent apoptotic/necrotic cell death. However, yeast cells that escape this first cell membrane disruption, particularly evident on sub-lethal concentration, die by metacaspase-mediated apoptosis induced by the accumulation of intracellular ROS. The deleted mutant on the yca1 gene showed high tolerance to citral and geraniol.

Antimicrobial Activity of Lemongrass Essential Oil (Cymbopogon flexuosus) and Its Active Component Citral Against Dual-Species Biofilms of Staphylococcus aureus and Candida Species

Compared to mono-species biofilm, biofilms formed by cross-kingdom pathogens are more refractory to conventional antibiotics, thus complicating clinical treatment and causing significant morbidity. Lemongrass essential oil and its bioactive component citral were previously demonstrated to possess strong antimicrobial efficacy against pathogenic bacteria and fungi. However, their effects on polymicrobial biofilms remain to be determined. In this study, the efficacy of lemongrass (Cymbopogon flexuosus) essential oil and its bioactive part citral against dual-species biofilms formed by Staphylococcus aureus and Candida species was evaluated in vitro. Biofilm staining and viability test showed both lemongrass essential oil and citral were able to reduce biofilm biomass and cell viability of each species in the biofilm. Microscopic examinations showed these agents interfered with adhesive characteristics of each species and disrupted biofilm matrix through counteracting nucleic acids, proteins and carbohydrates in the biofilm. Moreover, transcriptional analyses indicated citral downregulated hyphal adhesins and virulent factors of Candida albicans, while also reducing expression of genes involved in quorum sensing, peptidoglycan and fatty acids biosynthesis of S. aureus. Taken together, our results demonstrate the potential of lemongrass essential oil and citral as promising agents against polymicrobial biofilms as well as the underlying mechanisms of their activity in this setting.

Differential Antifungal Efficiency of Geraniol and Citral

Terpenoids such as geraniol and citral are known to have antibacterial, antifungal and anti-cancerous properties; however, their mechanism of action is least understood. In this study, the antifungal mechanism of monoterpene alcohol (geraniol) and monoterpene aldehyde (citral) was studied using Saccharomyces cerevisiae throughout 120 h duration and over a maximum tolerable dosage of 0.5% (v/v). Cell growth studies using optical density readings at 600 nm (ODλ=600nm), Cell viability using MTT assay, Na+/K+ leakage into media, osmotic stress using flame photometry, detection of metabolites like dehydroergosterol (DHE), H2O2 using fluorescence spectroscopy, changes in functional group analysis using FT-IR, elemental analysis using EDAX, DNA damage using gel electrophoresis and cellular structural changes using SEM were carried out. Growth inhibition studies using ODλ=600nm and MTT assays suggest that both geraniol and citral inhibited the growth kinetics significantly up to 0.1% v/v at and significantly increased beyond 0.1% at all the studied time points. Both the monoterpenoids induced the osmotic stress in S. cerevisiae measured as a change in reduction in pH, [H]+ concentration, with elevation in [Na]+ and [K]+ leakage into the media. Geraniol treatment reduced the levels of metabolites, dehydroergosterol (DHE) and H2O2, in a time-dependent manner whereas citral only affected their levels at 120 h. Energy dispersive X - ray spectroscopy (EDAX) studies suggest that both the monoterpenoids treatment differentially modulated the cellular elemental contents. Geraniol (0.03% v/v) and not the citral treatment induced DNA damage. Cellular structural analysis showed that both monoterpenoids have differential damaging effects to S. cerevisiae. This study shows that having an aldehyde and alcohol group on the terpenoids strongly affect the anti-fungal activity.

Ionic Liquid-Promoted Synthesis of Novel Chromone-Pyrimidine Coupled Derivatives, Antimicrobial Analysis, Enzyme Assay, Docking Study and Toxicity Study

Herein, we report an environmentally friendly, rapid, and convenient ionic liquid ([Et₃NH][HSO₄])-promoted facile synthesis of ethyl 4-(6-substituted-4-oxo-4H-chromen-3-yl)-6-methyl-2-thioxo/oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate derivatives 4(a–f) and 4-(6-substituted-4-oxo-4H-chromen-3-yl)-6-methyl-2-thioxo/oxo-1,2,3,4-tetrahydropyrimidine-5- carbohydrazide derivatives 6(a–f). All the synthesized derivatives 4(a–f) and 6(a–f) were evaluated for their in vitro antifungal and antibacterial activity, by method recommended by National Committee for Clinical Laboratory Standards (NCCLS). The compound 6c bearing a fluoro group on the chromone ring and oxygen and a hydrazino group (–NHNH₂) on the pyrimidine ring, was found to be the most potent antibacterial compound amongst the synthesized derivatives. The compound 6f bearing a methoxy group (–OCH₃) on the chromone ring and sulphur group on the pyrimidine ring, was found to exhibit equipotent antifungal activity when compared with the standard drug miconazole. A d-alanine-d-alanine ligase (DdlB) enzyme assay study and an ergosterol extraction and quantitation assay study were performed to predict the mode of action of the synthesized compounds. A molecular docking study was performed to predict the binding interactions with receptors and mode of action of the synthesized derivatives. Further, analysis of the ADMET parameters for the synthesized compounds has shown that these compounds have good oral drug-like properties and can be developed as oral drug candidates. To establish the antimicrobial selectivity and safety, the most active compounds 6c and 6f were further tested for cytotoxicity against the human cancer cell line HeLa and were found to be non-cytotoxic in nature. An in vivo acute oral toxicity study was also performed for the most active compounds 6c and 6f and the results indicated that the compounds are non-toxic in nature.

Antifungal Activity of Essential Oils against Candida albicans Strains Isolated from Users of Dental Prostheses

Objective

The objective of this study was to analyze the antifungal activity of citral, selected by screening natural products, against Candida albicans isolates from subjects who use dental prostheses.

Methodology

Screening of essential oils, including those from Mentha piperita L. (Briq), Origanum vulgare, and Zingiber officinale L., and the phytoconstituents citral and limonene, to select an appropriate natural product. Citral, which mediated the best antifungal response, was selected for biological assays. The minimum inhibitory concentrations (MICs) and minimum fungicidal concentrations (MFCs) for citral and nystatin were determined by the microdilution method. Micromorphological analyses, time-kill curve, and modulation tests were performed.

Results

The MIC and MFC of citral were established as 32 μg/mL, consistent with fungicidal activity. The clinical strains were resistant to nystatin. Citral caused micromorphological alteration in the strains. In the time-kill curve, the growth of the clinical strain was reduction in growth equal to 3 log₁₀ colony-forming units per milliliter after exposure to the MIC and MIC × 2 of citral for 2 h. Citral did not modulate the resistance of the studied strains to nystatin.

Conclusion

This study revealed the potential of citral as a fungicidal agent and highlighted the resistance of clinical strains of C. albicans to nystatin.

Facile Synthesis of Novel Coumarin Derivatives, Antimicrobial Analysis, Enzyme Assay, Docking Study, ADMET Prediction and Toxicity Study

The work reports the synthesis under solvent-free condition using the ionic liquid [Et₃NH][HSO₄] as a catalyst of fifteen novel 3-((dicyclohexylamino)(substituted phenyl/heteryl)-methyl)-4-hydroxy-2H-chromen-2-onederivatives 4a-o as potential antimicrobial agents. The structures of the synthesized compounds were confirmed by IR, ¹H-NMR, ¹³C-NMR, mass spectral studies and elemental analyses. All the synthesized compounds were evaluated for their in vitro antifungal and antibacterial activity. The compound 4k bearing 4-hydroxy-3-ethoxy group on the phenyl ring was found to be the most active antifungal agent. The compound 4e bearing a 2,4-difluoro group on the phenyl ring was found to be the most active antibacterial agent. The mode of action of the most promising antifungal compound 4k was established by an ergosterol extraction and quantitation assay. From the assay it was found that 4k acts by inhibition of ergosterol biosynthesis in C. albicans. Molecular docking studies revealed a highly spontaneous binding ability of the tested compounds to the active site of lanosterol 14α-demethylase, which suggests that the tested compounds inhibit the synthesis of this enzyme. The synthesized compounds were analyzed for in silico ADMET properties to establish oral drug like behavior and showed satisfactory results. To establish the antimicrobial selectivity and safety, the most active compounds 4e and 4k were further tested for cytotoxicity against human cancer cell line HeLa and were found to be non-cytotoxic in nature. An in vivo acute oral toxicity study was also performed for the most active compounds 4e and 4k and results indicated that the compounds are non-toxic.

Investigating the antifungal activity and mechanism(s) of geraniol against Candida albicans strains

Candida albicans can be a yeast that is a commensal on the human body but can cause opportunistic or pathogenic infections. Candida infections may create serious health problems and as a result has initiated a search for new drugs with an antifungal action. Geraniol is an acyclic monoterpene alcohol with known pharmacological properties, including antimicrobial activity. The aim of this work was to evaluate the antifungal activity and mechanism(s) of geraniol against C. albicans strains. The minimum inhibitory concentration (MIC) was determined through broth microdilution techniques. We investigated possible geraniol activity on the fungal cell wall (sorbitol protect effect), cell membrane (geraniol to ergosterol binding), the time-kill curve, and its biological activity on the yeast's morphology. Amphotericin B was used as control, and all tests were performed in duplicate. The MIC of geraniol was 16 μg/ml (for 90% of isolates) but its probable mechanism of action did not involve the cell wall and ergosterol binding. In the morphological interference assay, we observed that the product inhibited pseudohyphae and chlamydoconidia formation. Time-dependent kill curve assay demonstrated that the fungicidal activity for MIC × 2 started at 2 h for the ATCC 76485 strain, and at 4 h for the LM-70 strain. Geraniol showed in vitro antifungal potential against strains of C. albicans but did not involve action on the cell wall or ergosterol. This study contributes to the development of new antifungal drugs, especially against Candida spp.

Evaluation of Antifungal Activity and Mechanism of Action of Citral against Candida albicans

Candida albicans is a yeast that commensally inhabits the human body and can cause opportunistic or pathogenic infections. Objective. To investigate the antifungal activity of citral against C. albicans. Methodology. The minimum inhibitory concentration (MIC) and the minimum fungicidal concentration (MFC) were determined by the broth microdilution techniques. We also investigated possible citral action on cell walls (0.8 M sorbitol), cell membranes (citral to ergosterol binding), the time-kill curve, and biological activity on the yeast's morphology. Results. The MIC and MFC of citral were, respectively, 64 µg/mL and 256 µg/mL. Involvement with the cell wall and ergosterol binding were excluded as possible mechanisms of action. In the morphological interference assay, it was observed that the product inhibited pseudohyphae and chlamydoconidia formation. The MIC and the MFC of citral required only 4 hours of exposure to effectively kill 99.9% of the inoculum. Conclusion. Citral showed in vitro antifungal potential against strains of C. albicans. Citral's mechanism of action does not involve the cell wall or ergosterol, and further study is needed to completely describe its effects before being used in the future as a component of new antifungals.