Synergistic effect of the flavonoid catechin, quercetin, or epigallocatechin gallate with fluconazole induces apoptosis in Candida tropicalis resistant to fluconazole

Enhancement of ROS Production by Catechin Is a Primary Effect of Increased Azole Efficacy in Nakaseomyces glabratus (Candida glabrata) Cells Lacking the ERG6 Gene

Fungal infections have become an important public health problem. Currently, there are only three available classes of antifungals for the treatment of invasive infections. Two of them, azoles and polyenes, target the synthesis of ergosterol or bind to sterols. A promising strategy to improve current therapies is the use of natural compounds in combinational therapies with the existing antifungals. In this work, we analyzed the changes in the susceptibility of the mutant strain of Nakaseomyces glabratus (Candida glabrata) lacking the ERG6 gene (encoding the sterol C-24 methyltransferase in ergosterol biosynthesis) in the presence of catechin and antifungal azoles. The reduced content of ergosterol in the Cgerg6Δ mutant resulted in the increased tolerance of the mutant cells to both azoles and polyenes. The combination of catechin with fluconazole or miconazole led to the growth inhibition of the azole-resistant Cgerg6Δ mutant strain. In the presence of catechin and miconazole, the Cgerg6Δ mutant fails to properly activate the expression of genes encoding the transcription factors CgYap1p and CgMsn4p, as well as the gene expression of CgCTA1, which are involved in oxidative stress response and lead to the intracellular accumulation of ROS. Finally, we show that catechin administration reduces mortality in a Galleria mellonella model infected with C. glabrata. Our work thus supports the use of catechin in combination therapies for fungal infections and shows that the CgERG6 gene could be a potential new drug target.

Nitrogen-Containing Flavonoids-Preparation and Biological Activity

In this work, we report the application of Buchwald-Hartwig amination for the preparation of new derivatives of quercetin and luteolin. Our investigation delves into the impact of aniline moiety on antioxidant, and anti-inflammatory activity, cytotoxicity, and the ability of flavonoids to modulate drug-resistance mechanisms in bacteria. The anti-inflammatory activity disappeared after the introduction of aniline into the flavonoids and the cytotoxicity remained low. Although the ability of quercetin and luteolin to modulate bacterial resistance to antibiotics has already been published, this is the first report on the molecular mechanism of this process. Both flavonoids attenuate erythromycin resistance by suppressing the ribosomal methyltransferase encoded by the ermA gene in Staphylococcus aureus. Notably, 4-(trifluoromethyl)anilino quercetin emerged as a potent ErmA inhibitor, likely by interacting with the RNA-binding pocket of ErmA. Additionally, both 4-fluoroanilino derivatives effectively impended the staphylococcal efflux system. All the prepared derivatives exhibited superior activity in modulating gentamicin resistance in S. aureus compared to the parent compounds. Overall, the incorporation of substituted anilines into the flavonoid core significantly enhanced its ability to combat multidrug resistance in bacteria.

The Molecular Mechanisms and Therapeutic Potential of Cranberry, D-Mannose, and Flavonoids against Infectious Diseases: The Example of Urinary Tract Infections

The treatment of infectious diseases typically includes the administration of anti-infectives; however, the increasing rates of antimicrobial resistance (AMR) have led to attempts to develop other modalities, such as antimicrobial peptides, nanotechnology, bacteriophages, and natural products. Natural products offer a viable alternative due to their potential affordability, ease of access, and diverse biological activities. Flavonoids, a class of natural polyphenols, demonstrate broad anti-infective properties against viruses, bacteria, fungi, and parasites. Their mechanisms of action include disruption of microbial membranes, inhibition of nucleic acid synthesis, and interference with bacterial enzymes. This review explores the potential of natural compounds, such as flavonoids, as an alternative therapeutic approach to combat infectious diseases. Moreover, it discusses some commonly used natural products, such as cranberry and D-mannose, to manage urinary tract infections (UTIs). Cranberry products and D-mannose both, yet differently, inhibit the adhesion of uropathogenic bacteria to the urothelium, thus reducing the likelihood of UTI occurrence. Some studies, with methodological limitations and small patient samples, provide some encouraging results suggesting the use of these substances in the prevention of recurrent UTIs. While further research is needed to determine optimal dosages, bioavailability, and potential side effects, natural compounds hold promise as a complementary or alternative therapeutic strategy in the fight against infectious diseases.

Bioprospecting, Synergistic Antifungal and Toxicological Aspects of the Hydroxychalcones and Their Association with Azole Derivates against Candida spp. for Treating Vulvovaginal Candidiasis

Vulvovaginal candidiasis (VVC) remains a prevalent fungal disease, characterized by challenges, such as increased fungal resistance, side effects of current treatments, and the rising prevalence of non-albicans Candida spp. naturally more resistant. This study aimed to propose a novel therapeutic approach by investigating the antifungal properties and toxicity of 2-hydroxychalcone (2-HC) and 3'-hydroxychalcone (3'-HC), both alone and in combination with fluconazole (FCZ) and clotrimazole (CTZ). A lipid carrier (LC) was also developed to deliver these molecules. The study evaluated in vitro anti-Candida activity against five Candida species and assessed cytotoxicity in the C33-A cell line. The safety and therapeutic efficacy of in vivo were tested using an alternative animal model, Galleria mellonella. The results showed antifungal activity of 2-HC and 3'-HC, ranging from 7.8 to 31.2 as fungistatic and 15.6 to 125.0 mg/L as fungicide effect, with cell viability above 80% from a concentration of 9.3 mg/L (2-HC). Synergistic and partially synergistic interactions of these chalcones with FCZ and CTZ demonstrated significant improvement in antifungal activity, with MIC values ranging from 0.06 to 62.5 mg/L. Some combinations reduced cytotoxicity, achieving 100% cell viability in many interactions. Additionally, two LCs with suitable properties for intravaginal application were developed. These formulations demonstrated promising therapeutic efficacy and low toxicity in Galleria mellonella assays. These results suggest the potential of this approach in developing new therapies for VVC.

Globospiramine Exhibits Inhibitory and Fungicidal Effects against Candida albicans via Apoptotic Mechanisms

Candidiasis is considered an emerging public health concern because of the occurrence of drug-resistant Candida strains and the lack of an available structurally diverse antifungal drug armamentarium. The indole alkaloid globospiramine from the anticandidal Philippine medicinal plant Voacanga globosa exhibits a variety of biological activities; however, its antifungal properties remain to be explored. In this study, we report the in vitro anticandidal activities of globospiramine against two clinically relevant Candida species (C. albicans and C. tropicalis) and the exploration of its possible target proteins using in silico methods. Thus, the colony-forming unit (CFU) viability assay revealed time- and concentration-dependent anticandidal effects of the alkaloid along with a decrease in the number of viable CFUs by almost 50% at 60 min after treatment. The results of the MIC and MFC assays indicated inhibitory and fungicidal effects of globospiramine against C. albicans (MIC = 8 µg/mL; MFC = 8 µg/mL) and potential fungistatic effects against C. tropicalis at lower concentrations (MIC = 4 µg/mL; MFC > 64 µg/mL). The FAM-FLICA poly-caspase assay showed metacaspase activation in C. albicans cells at concentrations of 16 and 8 µg/mL, which agreed well with the MIC and MFC values. Molecular docking and molecular dynamics simulation experiments suggested globospiramine to bind strongly with 1,3-β-glucan synthase and Als3 adhesin-enzymes indirectly involved in apoptosis-driven candidal inhibition.

A mechanism study on the synergistic effects of rifapentine and fluconazole against fluconazole-resistant Candida albicans in vitro

Candida albicans (C. albicans) is one of the most common clinical isolates of systemic fungal infection. Long-term and inappropriate use of antifungal drugs can cause fungal resistance, which poses a great challenge to the clinical treatment of fungal infections. The combination of antifungal drugs and non-antifungal drugs to overcome the problem of fungal resistance has become a research hotspot in recent years. Our previous study found that the combination of rifapentine (RFT) and fluconazole (FLC) has a significant synergistic against FLC-resistant C. albicans. The present study aimed to further verify the synergistic effect between FLC and RFT against the FLC-resistant C. albicans 100, and explore the underlying mechanism. The growth curve and spot assay test not only showed the synergistic effect of FLC and RFT on FLC-resistant C. albicans in vitro but exhibited a dose-dependent effect on RFT, indicating that RFT may play a principal role in the synergic effect of the two drugs. Flow cytometry showed that the combined use of RFT and FLC arrested cells in the G2/M phase, inhibiting the normal division and proliferation of FLC-resistant C. albicans. Transmission electron microscopy (TEM) demonstrated that FLC at a low concentration could still cause a certain degree of damage to the cell membrane in the FLC-resistant C. albicans, as represented by irregular morphologic changes and some defects observed in the cell membrane. When FLC was used in combination with RFT, the nuclear membrane was dissolved and the nucleus was condensed into a mass. Detection of the intracellular drug concentration of fungi revealed that the intracellular concentration of RFT was 31-195 fold that of RFT alone when it was concomitantly used with FLC. This indicated that FLC could significantly increase the concentration of RFT in cells, which may be due to the damage caused to the fungal cell membrane by FLC. In short, the present study revealed a synergistic mechanism in the combined use of RFT and FLC, which may provide a novel strategy for the clinical treatment of FLC-resistant C. albicans.

Specifically Targeting Metacaspases of Candida: A New Therapeutic Opportunity

The World Health Organization (WHO) recently published a list of fungal priority pathogens, including Candida albicans and C. auris. The increased level of resistance of Candida is raising concern, considering the availability of only four classes of medicine. The WHO is seeking novel agent classes with different targets and mechanisms of action. Targeting Candida metacaspases to control intrinsic cell death could provide new therapeutic opportunities for invasive candidiasis. In this review, we provide the available evidence for Candida cell death, describe Candida metacaspases, and discuss the potential of Candida metacaspases to offer a new specific target. Targeting Candida cell death has good scientific rationale given that the fungicidal activity of many marketed antifungals is mediated, among others, by cell death triggering. But none of the available antifungals are specifically activating Candida metacaspases, making this target a new therapeutic opportunity for non-susceptible isolates. It is expected that antifungals based on the activation of fungi metacaspases will have a broad spectrum of action, as metacaspases have been described in many fungi, including filamentous fungi. Considering this original mechanism of action, it could be of great interest to combine these new antifungal candidates with existing antifungals. This approach would help to avoid the development of antifungal resistance, which is especially increasing in Candida.

The Changes in Metabolites, Quality Components, and Antioxidant Activity of Tea (Camellia sinensis) Infected with Exobasidium vexans by Applying UPLC-MS/MS-Based Widely Targeted Metabolome and Biochemical Analysis

Blister blight infection with Exobasidium vexans is one of the most destructive foliar diseases that seriously affect the quality and yield of tea. This research investigated the metabolite changes of healthy and infected leaves on tea cultivar 'Fuding Dabaicha' and further explored the potential antimicrobial substances against E. vexans infection. In total, 1,166 compounds were identified during the entire course of an infection, among which 73 different common compounds were significantly accumulated involved in the important antimicrobial substances of flavonoids and phenolic acids, including kaempferol (3,5,7,4'-tetrahydroxyflavone), kaempferol-3-O-sophoroside-7-O-glucoside, phloretin, 2,4,6-trihydroxybenzoic acid, galloylprocyanidin B4, and procyanidin C1 3'-O-gallate, which indicated that these metabolites might positively dominate resistance to E. vexans. Furthermore, relevant biological pathways, such as the flavone and flavonol biosynthesis, flavonoid biosynthesis, and phenylpropane pathways, were more closely related to resistance to E. vexans. Additionally, total flavonoids, phenolics, alkaloids, and terpenoids contributing to antimicrobial and antioxidant capacity were significantly altered during four different infection periods, especially the Leaf_S2 stage (the second stage of infection), in which the most concentration accumulated. The leaves affected by E. vexans infection at the second stage had the relatively highest antioxidant activity. Accordingly, this study provides a theoretical support for and comprehensive insights into the effects on the metabolite changes, tea quality components, and antioxidant activity of blister blight caused by E. vexans.

The elucidation of the multimodal action of the investigational anti-Candida lipopeptide (AF4) lead from Bacillus subtilis

Background: Candida species are the main etiological agents for candidiasis, and Candida albicans are the most common infectious species. Candida species' growing resistance to conventional therapies necessitates more research into novel antifungal agents. Antifungal peptides isolated from microorganisms have potential applications as novel therapeutics. AF4 a Bacillus-derived lipopeptide demonstrating broad-spectrum antifungal activity has been investigated for its ability to cause cell death in Candida species via membrane damage and oxidative stress. Methods: Using biophysical techniques, the secondary structure of the AF4 lipopeptide was identified. Scanning electron microscopy and confocal microscopy with fluorescent dyes were performed to visualise the effect of the lipopeptide. The membrane disruption and permeabilization were assessed using the 1,6-diphenyl hexatriene (DPH) fluorescence assay and flow cytometric (FC) assessment of propidium iodide (PI) uptake, respectively. The reactive oxygen species levels were estimated using the FC assessment. The induction of apoptosis and DNA damage were studied using Annexin V-FITC/PI and DAPI. Results: Bacillus-derived antifungal variant AF4 was found to have structural features typical of lipopeptides. Microscopy imaging revealed that AF4 damages the surface of treated cells and results in membrane permeabilization, facilitating the uptake of the fluorescent dyes. A loss of membrane integrity was observed in cells treated with AF4 due to a decrease in DPH fluorescence and a dose-dependent increase in PI uptake. Cell damage was also determined from the log reduction of viable cells treated with AF4. AF4 treatment also caused elevated ROS levels, induced phosphatidylserine externalisation, late-stage apoptosis, and alterations to nuclear morphology revealed by DAPI fluorescence. Conclusion: Collectively, the mode of action studies revealed that AF4 acts primarily on the cell membrane of C. albicans and has the potential to act as an antifungal drug candidate.

Catechin potentiates the antifungal effect of miconazole in Candida glabrata

The rising number of invasive fungal infections caused by drug-resistant Candida strains is one of the greatest challenges for the development of novel antifungal strategies. The scarcity of available antifungals has drawn attention to the potential of natural products as antifungals and in combinational therapies. One of these is catechins-polyphenolic compounds-flavanols, found in a variety of plants. In this work, we evaluated the changes in the susceptibility of Candida glabrata strain characterized at the laboratory level and clinical isolates using the combination of catechin and antifungal azoles. Catechin alone had no antifungal activity within the concentration range tested. Its use in combination with miconazole resulted in complete inhibition of growth in the sensitive C. glabrata isolate and a significant growth reduction in the azole resistant C. glabrata clinical isolate. Simultaneous use of catechin and miconazole leads to increased intracellular ROS generation. The enhanced susceptibility of C. glabrata clinical isolates to miconazole by catechin was accompanied with the intracellular accumulation of ROS and changes in the plasma membrane permeability, as measured using fluorescence anisotropy, affecting the function of plasma membrane proteins.

Quercetin protects against Aspergillus fumigatus keratitis by reducing fungal load and inhibiting TLR-4 induced inflammatory response

PURPOSE

To investigate the antifungal and anti-inflammatory effects of quercetin in Aspergillus fumigatus (A. fumigatus) keratitis.

METHODS

Draize eye test was performed in mice to evaluate the toxicity of quercetin, and the antifungal effects on A. fumigatus were assessed via scanning electron microscopy (SEM), propidium iodide uptake, and adherence assay. In fungal keratitis (FK) mouse models, immunostaining was performed for investigating toll-like receptor 4 (TLR-4) expression and macrophage infiltration. Real-time PCR, ELISA, and Western blot were used to evaluate the expression of pro-inflammatory factors IL-1β, TNF-α, and IL-6 in infected RAW264.7 cells. Cells were also treated with TLR-4 siRNA or agonist CRX-527 to investigate mechanisms underlying the anti-inflammatory activity of quercetin.

RESULTS

Quercetin at 32 μM was non-toxic to corneal epithelial and significantly inhibited A. fumigatus growth and adhesion, and also altered the structure and reduced the number of mycelia. Quercetin significantly reduced macrophage infiltration in the mouse cornea, and attenuated the expression of TLR-4 in the corneal epithelium and stroma of mice with keratitis caused by A. fumigatus. In RAW264.7 cells infected by A. fumigatus, quercetin downregulated TLR-4 along with pro-inflammatory factors IL-1β, TNF-α, and IL-6. RAW cells with TLR-4 knockdown had reduced expression of factors after A. fumigatus infection, which was decreased even further with quercetin treatment. In contrast, cells with CRX-527 had elevated inflammatory factors compared to control, which was significantly attenuated in the presence of quercetin.

CONCLUSION

Quercetin plays a protective role in mouse A. fumigatus keratitis by inhibiting fungal load, disrupting hyphae structure, macrophage infiltration, and suppressing inflammation response in macrophages via TLR-4 mediated signaling pathway.

Functional Characterization of a Bacillus-Derived Novel Broad-Spectrum Antifungal Lipopeptide Variant against Candida tropicalis and Candida auris and Unravelling Its Mode of Action

Limited treatment options, recalcitrance, and resistance to existing therapeutics encourage the discovery of novel antifungal leads for alternative therapeutics. Antifungal lipopeptides have emerged as potential candidates for developing new and alternative antifungal therapies. In our previous studies, we isolated and identified the lipopeptide variant AF4 and purified it to homogeneity via chromatography from the cell-free supernatant of Bacillus subtilis. AF4 was found to have broad-spectrum antifungal activity against more than 110 fungal isolates. In this study, we found that clinical isolates of Candida tropicalis and Candida auris exposed to AF4 exhibited low MICs of 4 to 8 mg/L. Time-kill assays indicated the in vitro pharmacodynamic potential of AF4. Biocompatibility assays demonstrated ~75% cell viability at 8 mg/L of AF4, indicating the lipopeptide's minimally cytotoxic nature. In lipopeptide-treated C. tropicalis and C. auris cells, scanning electron microscopy revealed damage to the cell surface, while confocal microscopy with acridine orange(AO)/propidium iodide (PI) and FUN-1 indicated permeabilization of the cell membrane, and DNA damage upon DAPI (4',6-diamidino-2-phenylindole) staining. These observations were corroborated using flow cytometry (FC) in which propidium iodide, 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA), and rhodamine 123 (Rh123) staining of cells treated with AF4 revealed loss of membrane integrity, increased reactive oxygen species (ROS) production, and mitochondrial membrane dysfunction, respectively. Membrane perturbation was also observed in the 1,6-diphenyl-1,3,5-hexatriene (DPH) fluorescence study and the interaction with ergosterol was observed by an ergosterol binding assay. Decreased membrane dipole potential also indicated the probable binding of lipopeptide to the cell membrane. Collectively, these findings describe the mode of action of AF4 against fungal isolates by membrane disruption and ROS generation, demonstrating its antifungal potency. IMPORTANCE C. tropicalis is a major concern for candidiasis in India and C. auris has emerged as a resistant yeast causing difficult-to-treat infections. Currently, amphotericin B (AMB) and 5-flucytosine (5-FC) are the main therapeutics for systemic fungal infections; however, the nephrotoxicity of AMB and resistance to 5-FC is a serious concern. Antifungal lead molecules with low adverse effects are the need of the hour. In this study, we briefly describe the antifungal potential of the AF4 lipopeptide and its mode of action using microscopy, flow cytometry, and fluorescence-based assays. Our investigation reveals the basic mode of action of the investigated lipopeptide. This lipopeptide with broad-spectrum antifungal potency is apparently membrane-active, and there is a smaller chance that organisms exposed to such a compound will develop drug resistance. It could potentially act as a lead molecule for the development of an alternative antifungal agent to combat candidiasis.

Effects of green tea extract epigallocatechin-3-gallate (EGCG) on oral disease-associated microbes: a review

For thousands of years, caries, periodontitis and mucosal diseases, which are closely related to oral microorganisms, have always affected human health and quality of life. These complex microbiota present in different parts of the mouth can cause chronic infections in the oral cavity under certain conditions, some of which can also lead to acute and systemic diseases. With the mutation of related microorganisms and the continuous emergence of drug-resistant strains, in order to prevent and treat related diseases, in addition to the innovation of diagnosis and treatment technology, the development of new antimicrobial drugs is also important. Catechins are polyphenolic compounds in green tea, some of which are reported to provide health benefits for a variety of diseases. Studies have shown that epigallocatechin-3-gallate (EGCG) is the most abundant and effective active ingredient in green tea catechins, which acts against a variety of gram-positive and negative bacteria, as well as some fungi and viruses. This review aims to summarize the research progress on the activity of EGCG against common oral disease-associated organisms and discuss the mechanisms of these actions, hoping to provide new medication strategies for the prevention and treatment of oral infectious diseases, the future research of EGCG and its translation into clinical practice are also discussed.

Bioactivity and Therapeutic Potential of Kaempferol and Quercetin: New Insights for Plant and Human Health

Plant secondary metabolites, especially flavonoids, are major metabolites widely found in plants that play several key roles in plant defence and signalling in response to stress conditions. The most studied among these flavonoids are kaempferol and quercetin due to their anti-oxidative potential and their key roles in the defence system, making them more critical for plant adaptation in stress environments. Kaempferol and quercetin in plants have great therapeutic potential for human health. Despite being well-studied, some of their functional aspects regarding plants and human health need further evaluation. This review summarizes the emerging potential of kaempferol and quercetin in terms of antimicrobial activity, bioavailability and bioactivity in the human body as well as in the regulation of plant defence in response to stresses and as a signalling molecule in terms of hormonal modulation under stress conditions. We also evaluated the safe use of both metabolites in the pharmaceutical industry.

Antifungal Activity of Mexican Propolis on Clinical Isolates of Candida Species

Infections caused by micro-organisms of the genus Candida are becoming a growing health problem worldwide. These fungi are opportunistic commensals that can produce infections—clinically known as candidiasis—in immunocompromised individuals. The indiscriminate use of different anti-fungal treatments has triggered the resistance of Candida species to currently used therapies. In this sense, propolis has been shown to have potent antimicrobial properties and thus can be used as an approach for the inhibition of Candida species. Therefore, this work aims to evaluate the anti-Candida effects of a propolis extract obtained from the north of Mexico on clinical isolates of Candida species. Candida species were specifically identified from oral lesions, and both the qualitative and quantitative anti-Candida effects of the Mexican propolis were evaluated, as well as its inhibitory effect on C. albicans isolate’s germ tube growth and chemical composition. Three Candida species were identified, and our results indicated that the inhibition halos of the propolis ranged from 7.6 to 21.43 mm, while that of the MFC and FC₅₀ ranged from 0.312 to 1.25 and 0.014 to 0.244 mg/mL, respectively. Moreover, the propolis was found to inhibit germ tube formation (IC₅₀ ranging from 0.030 to 1.291 mg/mL). Chemical composition analysis indicated the presence of flavonoids, including pinocembrin, baicalein, pinobanksin chalcone, rhamnetin, and biochanin A, in the Mexican propolis extract. In summary, our work shows that Mexican propolis presents significant anti-Candida effects related to its chemical composition, and also inhibits germ tube growth. Other Candida species virulence factors should be investigated in future research in order to determine the mechanisms associated with antifungal effects against them.

Application of Phytochemicals To Combat Fungal Pathogens of Pulses: An Approach toward Inhibition of Fungal Propagation and Invasin Activity

The present study represented an innovative strategy for inactivating the secreted invasins (lignocellulolytic enzymes) of fungal phytopathogens using natural phytochemicals to combat fungal infection to the pulses. A fungal pathogen (Aspergillus niger SKP1) was isolated from the white lentil (Vigna mungo), which has the ability to synthesize different lignocellulolytic enzymes. An in silico docking study elucidated that quercetin, naringin, epigallocatechin gallate, curcumin, and cinnamic acid were the prime efficient phytochemicals to inhibit the activity of fungal invasive enzymes like endoglucanase, endo-1,4-β-xylanase, and glucoamylase. Considering this observation, extracted phytochemicals in different mixtures were applied to prevent growth of the isolated pathogen under in situ experimental studies. The minimal inhibitory concentrations (MIC₅₀) and minimal fungicidal concentration (MFC₅₀) values of the first mixture (naringenin, epicatechin gallate, and cinnamic acid) and second mixture (quercetin and curcumin) were 170 and 220 mg/L and 320 and 380 mg/L, respectively. The studied phytochemicals were established to be cytosafe when compared to the commercial fungicides. The seeds of the white lentil were subjected to 1 year of long-term storage with the two aforementioned combinatorial phytochemicals. Subsequent morphological and physiological analyses revealed the complete protection of the stored seeds from the fungal infection. The present work has enough potentiality for the storage of pulses using natural preservatives that circumvent the adverse effect of the chemical preservatives on the ecosystem.

Phytochemical Analysis and Antifungal Potentiating Activity of Extracts from Loquat (Eriobotrya japonica) against Cryptococcus neoformans Clinical Isolates

Eriobotrya japonica (loquat) has been used in African traditional medicine with numerous beneficial health effects. The extracts from loquat contain several bioactive compounds with a plethora of pharmacological properties. However, a scientific study on the activity against the aetiological agent of cryptococcosis has not yet been reported. Therefore, this study aimed to investigate the antifungal potential of various extracts from Eriobotrya japonica against clinical isolates of Cryptococcus neoformans. Quantitative and qualitative phytochemical analyses of extracts were made by following standard procedures. The broth microdilution method and the checkerboard methods were used to determine the antifungal activity and the combination of extracts with antifungals drugs. The methanol extract of seeds and the hexane extract of leaves exhibited the best significant antifungal activity with MIC values of 32 µg/mL. Furthermore, the combination of both extracts with nystatin and clotrimazole showed synergistic interactions with a 32-fold reduction in the MIC values of nystatin. Our findings indicate that Eriobotrya japonica extracts are a potential source of new antifungals that could be developed for use in the treatment of cryptococcosis. The anticryptococcal and antifungal activities potentiating activity of the studied extracts indicate their potential in the management of cryptococcosis. Further study should be considered to identify the bioactive principles against Cryptococcus neoformans.

Antimicrobial Activity of Quercetin: An Approach to Its Mechanistic Principle

Quercetin, an essential plant flavonoid, possesses a variety of pharmacological activities. Extensive literature investigates its antimicrobial activity and possible mechanism of action. Quercetin has been shown to inhibit the growth of different Gram-positive and Gram-negative bacteria as well as fungi and viruses. The mechanism of its antimicrobial action includes cell membrane damage, change of membrane permeability, inhibition of synthesis of nucleic acids and proteins, reduction of expression of virulence factors, mitochondrial dysfunction, and preventing biofilm formation. Quercetin has also been shown to inhibit the growth of various drug-resistant microorganisms, thereby suggesting its use as a potent antimicrobial agent against drug-resistant strains. Furthermore, certain structural modifications of quercetin have sometimes been shown to enhance its antimicrobial activity compared to that of the parent molecule. In this review, we have summarized the antimicrobial activity of quercetin with a special focus on its mechanistic principle. Therefore, this review will provide further insights into the scientific understanding of quercetin’s mechanism of action, and the implications for its use as a clinically relevant antimicrobial agent.

Efficacy of Flavonoids in Combating Fluconazole Resistant Oral Candidiasis

BACKGROUND

Candida is an opportunistic fungus often present in the oral mucosa. In the compromised immune system, it may become pathogenic and cause oral candidiasis. This infection is more common with Candida albicans; though, non-albicans Candida spp also have significant relevance. Current treatment guidelines include polyenes, azoles and echinocandins, where fluconazole is the primary therapeutic option. However, both inherited and acquired resistance to fluconazole is exhaustively reported. The development of resistance has resulted in the worsening of the original and re-emergence of new fungal diseases. Thus, the development of an anti-candidiasis therapy with a satisfactory outcome is the urgent need of the hour.

OBJECTIVE

This review article aims to stimulate the research in establishing the synergistic efficacy of various flavonoids with fluconazole to combat the resistance and develop an effective pharmacotherapy for the treatment of oral candidiasis. Further, in this article, we discuss in detail the mechanisms of action of fluconazole, along with the molecular basis of development of resistance in Candida species.

METHOD

PubMed and other databases were used for literature search.

RESULTS

The designing of natural drugs from the plant- derived phytochemicals are the promising alternates in modern medicine. The challenge today is the development of alternative anti- oral candidiasis drugs with increased efficacy, bioavailability and better outcome which can combat azole resistance. Identifying the flavonoids with potential antifungal action at low concentrations seems to meet the challenges.

CONCLUSION

Phyto-active constituents, either alone or in combination with conventional antibiotics may be an effective approach to deal with global antimicrobial resistance. The efficacy of herbal therapy for decades suggests that bacteria, fungi, and viruses may have a reduced ability to adapt and resistance to these natural antimicrobial regimes.

An ethnopharmacological review on the therapeutical properties of flavonoids and their mechanisms of actions: A comprehensive review based on up to date knowledge

Flavonoids -a class of low molecular weight secondary metabolites- are ubiquitous and cornucopia throughout the plant kingdom. Structurally, the main structure consists of C6-C3-C6 rings with different substitution patterns so that many sub-classes are obtained, for example: flavonols, flavonolignans, flavonoid glycosides, flavans, anthocyanidins, aurones, anthocyanidins, flavones, neoflavonoids, chalcones, isoflavones, flavones and flavanones. Flavonoids are evaluated to have drug like nature since they possess different therapeutic activities, and can act as cardioprotective, antiviral, antidiabetic, anti-inflammatory, antibacterial, anticancer, and also work against Alzheimer's disease and others. However, information on the relationship between their structure and biological activity is scarce. Therefore, the present review tries to summarize all the therapeutic activities of flavonoids, their mechanisms of action and the structure activity relationship.

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Latest updated ethnopharmacological review of the therapeutic effects of flavonoids.

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Flavonoids are attracting attention because of their therapeutic properties.

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Flavonoids are valuable candidates for drug development against many dangerous diseases.

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This overview summarizes the most important therapeutic effect and mechanism of action of flavonoids.

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General knowledge about the structure activity relationship of flavonoids is summarized.

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Substitution of chemical groups in the structure of flavonoids can significantly change their biological and chemical properties.

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The chemical properties of the basic flavonoid structure should be considered in a drug-based structural program.

OUP accepted manuscript

Candida auris is an emerging, multi drug resistant fungal pathogen that has caused infectious outbreaks in over 45 countries since its first isolation over a decade ago, leading to in-hospital crude mortality rates as high as 72%. The fungus is also acclimated to disinfection procedures and persists for weeks in nosocomial ecosystems. Alarmingly, the outbreaks of C. auris infections in Coronavirus Disease-2019 (COVID-19) patients have also been reported. The pathogenicity, drug resistance and global spread of C. auris have led to an urgent exploration of novel, candidate antifungal agents for C. auris therapeutics. This narrative review codifies the emerging data on the following new/emerging antifungal compounds and strategies: antimicrobial peptides, combinational therapy, immunotherapy, metals and nano particles, natural compounds, and repurposed drugs. Encouragingly, a vast majority of these exhibit excellent anti- C. auris properties, with promising drugs now in the pipeline in various stages of development. Nevertheless, further research on the modes of action, toxicity, and the dosage of the new formulations are warranted. Studies are needed with representation from all five C. auris clades, so as to produce data of grater relevance, and broader significance and validity.

Eucalyptol/ β-cyclodextrin inclusion complex loaded gellan/PVA nanofibers as antifungal drug delivery system

Fungal infections pose a serious threat to humankind due to the toxicity of conventional antifungal therapy and continuous emerging incidence of multidrug resistance. Essential oils fascinated researchers because of their broad antimicrobial activity and minimal cytotoxicity. However, hydrophobic, volatile and low water solubility of essential oils hinder their applications in pharmaceutical industries. Therefore, in this study we have loaded eucalyptol/ β-cyclodextrin inclusion complex to gellan/polyvinyl alcohol nanofibers (EPNF) to eradicate Candida albicans and Candida glabrata biofilms. The electrospun nanofibers characterized by various physicochemical techniques and it was observed that EPNF possess highly hydrophilic surface property that facilitate rapid drug release. EPNF inhibited approximately 70% biofilm of C. albicans and C. glabrata. Time kill results depicted that eucalyptol (EPTL) encapsulation in the nanofibers prolonged its antifungal activity than the pure EPTL. Electron microscopy studies revealed that EPNF disrupted the cell surface of Candida. Collectively the current study suggested nanofiber encapsulation enhanced antibiofilm activity of eucalyptol and these nanoscale systems can serve as an alternative therapeutic strategy to treat fungal infections. Further, the developed nanofibrous materials can be applied as cost effective coating agent for biomedical implants.

Antifungal Activity of Extracts, Fractions, and Constituents from Coccoloba cowellii Leaves

Coccoloba cowellii Britton (Polygonaceae, order Caryophyllales) is an endemic and critically endangered plant species that only grows in the municipality of Camagüey, a province of Cuba. A preliminary investigation of its total methanolic extract led to the discovery of promising antifungal activity. In this study, a bioassay-guided fractionation allowed the isolation of quercetin and four methoxyflavonoids: 3-O-methylquercetin, myricetin 3,3′,4′-trimethyl ether, 6-methoxymyricetin 3,4′-dimethyl ether, and 6-methoxymyricetin 3,3′,4′-trimethyl ether. The leaf extract, fractions, and compounds were tested against various fungi and showed strong in vitro antifungal activity against Cryptococcus neoformans and various Candida spp. with no cytotoxicity (CC₅₀ > 64.0 µg/mL) on MRC-5 SV2 cells, determined by a resazurin assay. A Candida albicans SC5314 antibiofilm assay indicated that the antifungal activity of C. cowellii extracts and constituents is mainly targeted to planktonic cells. The total methanolic extract showed higher and broader activity compared with the fractions and mixture of compounds.

Nanotechnological Innovations Enhancing the Topical Therapeutic Efficacy of Quercetin: A Succinct Review

Nanotechnology is currently a hot topic in dermatology and nutraceutical/cosmeceutical delivery, owing to the advantages it provides in terms of enhancing the skin permeation of drugs, as well as increasing their therapeutic efficacy in the treatment of different dermatological diseases. There is also a great interest in the topical delivery of nutraceuticals; which are natural compounds with both therapeutic and cosmetic benefits, in order to overcome the side effects of topically applied chemical drugs. Quercetin is a key nutraceutical with topical antioxidant and anti-inflammatory properties which was reported to be effective in the treatment of different dermatological diseases, however, its topical therapeutic activity is hindered by its poor skin penetration. This review highlights the topical applications of quercetin, and summarizes the nanocarrier-based solutions to its percutaneous delivery challenges.

Synergistic potential of nutraceuticals: mechanisms and prospects for futuristic medicine

Nutraceuticals are valued for their therapeutic effects and numerous health benefits. In recent years, several studies have demonstrated their superior performances when co-delivered; the concept of synergism has been established for various bioactives. Apart from improvements in the bioavailability of partnering compounds, this approach can protect the radical scavenging potential and biological effects of individual compounds. In this review, the intricate mechanisms that promote synergistic effects when bioactive compounds are co-delivered are detailed. Importantly, a range of potential medical applications that have been established through such synergistic effects is presented, emphasizing recent developments in this field. Also, a section has been devoted to highlighting perspectives on co-encapsulation at the nanoscale for improved synergistic benefits. While prospects for the treatment of chronic diseases are well-demonstrated, several challenges and safety concerns remain, and these have been discussed, providing recommendations for future research.

Azole-triphenylphosphonium conjugates combat antifungal resistance and alleviate the development of drug-resistance

Azole antifungals are commonly used to treat fungal infections but have resulted in the occurrence of drug resistance. Therefore, developing azole derivatives (AZDs) that can both combat established drug-resistant fungal strains and evade drug resistance is of great importance. In this study, we synthesized a series of AZDs with a fluconazole (FLC) skeleton conjugated with a mitochondria-targeting triphenylphosphonium cation (TPP⁺). These AZDs displayed potent activity against both azole-sensitive and azole-resistant Candida strains without eliciting obvious resistance. Moreover, two representative AZDs, 20 and 25, exerted synergistic antifungal activity with Hsp90 inhibitors against C. albicans strains resistant to the combination treatment of FLC and Hsp90 inhibitors. AZD 25, which had minimal cytotoxicity, was effective in preventing C. albicans biofilm formation. Mechanistic investigation revealed that AZD 25 inhibited the biosynthesis of the fungal membrane component ergosterol and interfered with mitochondrial function. Our findings provide an alternative approach to address fungal resistance problems.

Synergistic antifungal effects of curcumin derivatives as fungal biofilm inhibitors with fluconazole

Lack of novel antifungal agents and severe drug resistance has led to high incidence and associated mortality of invasive fungal infections. To tackle the challenges, novel antifungal agents with anti-resistant potency are highly desirable. Thus, derivatives of curcumin were synthesized to restore the effectiveness of fluconazole (FLC) against FLC-resistant Candida spp. and structure-activity relationships were then discussed. Some novel derivatives showed promising features as novel antifungal lead compounds. Of them, compound 4 showed good alone or synergistic antifungal activity against FLC-resistant Candida spp. Moreover, compound 4 was proven as a potent inhibitor of Candida albicans biofilm formation and yeast-to-hypha morphological transition whether used alone or in combination with FLC, which was further confirmed by the inhibitory effect on cellular surface hydrophobicity of C. albicans. Compound 4 also inhibits intracellular ATP production of C. albicans and disrupts membrane permeability of C. albicans when used in combination with FLC. The results highlighted the potential of curcumin derivatives to overcome fluconazole-related and biofilm-related drug resistance.

Evaluation of the antifungal activity in vitro of midazolam against fluconazole-resistant Candida spp. isolates

Aim: The purpose of this study was to evaluate the antifungal activity of midazolam, alone and in association with azoles, against isolates of clinical Candida spp. in planktonic and biofilm form. Materials & methods: The antifungal activity was observed using the broth microdilution technique. Flow cytometry tests were performed to investigate the probable mechanism of action and the comet test and cytotoxicity test were applied to evaluate DNA damage. Results: Midazolam (MIDAZ) showed antifungal activity against planktonic cells (125-250 μg/ml) and reduced the viability of Candida spp. biofilms (125 a 2500 μg/ml). The interaction of MIDAZ against Candida spp. biofilms was observed through scanning electron microscopy, causing alteration of their appearance. Therefore, MIDAZ has antifungal potential against Candida spp.

Quercetin: Its Main Pharmacological Activity and Potential Application in Clinical Medicine

Quercetin is a flavonoid compound widely present in plants and exhibits a variety of biological activities. Research on quercetin has shown its potential for medical application. In this research, we elucidate its antioxidant mechanism and the broad-spectrum antibacterial and antiparasite properties; summarise its potential application in antioncology and cardiovascular protection and anti-immunosuppression treatment; and demonstrate its ability to alleviate the toxicity of mycotoxins. This research is expected to offer some insights and inspirations for the further study of quercetin, its properties, and the scientific basis for its better application in clinical practice.

Metabolic Profile of Scytalidium parasiticum-Ganoderma boninense Co-Cultures Revealed the Alkaloids, Flavonoids and Fatty Acids that Contribute to Anti-Ganoderma Activity

In solving the issue of basal stem rot diseases caused by Ganoderma, an investigation of Scytalidium parasiticum as a biological control agent that suppresses Ganoderma infection has gained our interest, as it is more environmentally friendly. Recently, the fungal co-cultivation has emerged as a promising method to discover novel antimicrobial metabolites. In this study, an established technique of co-culturing Scytalidium parasiticum and Ganoderma boninense was applied to produce and induce metabolites that have antifungal activity against G. boninense. The crude extract from the co-culture media was applied to a High Performance Liquid Chromatography (HPLC) preparative column to isolate the bioactive compounds, which were tested against G. boninense. The fractions that showed inhibition against G. boninense were sent for a Liquid Chromatography-Time of Flight-Mass Spectrometry (LC-TOF-MS) analysis to further identify the compounds that were responsible for the microbicidal activity. Interestingly, we found that eudistomin I, naringenin 7-O-beta-D-glucoside and penipanoid A, which were present in different abundances in all the active fractions, except in the control, could be the antimicrobial metabolites. In addition, the abundance of fatty acids, such as oleic acid and stearamide in the active fraction, also enhanced the antimicrobial activity. This comprehensive metabolomics study could be used as the basis for isolating biocontrol compounds to be applied in oil palm fields to combat a Ganoderma infection.

UPLC-MS-QTOF analysis and antifungal activity of Cumaru (Amburana cearensis)

This study was aimed at investigating the phytochemical constituents, antifungal properties and antibiotic-modifying activity of the aqueous crude extract and fractions of Amburana cearensis seeds (CEFAC). The CEFAC were chemically characterized by LC-MS/MS-QTOF. In addition, the antifungal activity was assayed by the microdilution method against strains of Candida albicans. The phytochemical profile of CEFAC exhibited phenolic compounds, organic acids, and polyphenols. The results of the assessment of antifungal activity reveled an IC₅₀ ranging from 45.6 to 2048 µg/mL. Interestingly, when CEFAC was associated with Fluconazole, we evidenced a decreased IC₅₀ (1.81-11.9 µg/mL), suggesting a synergism with antibiotic. It was possible to identify in the crude extract and fractions several phenolic compounds, organic acids, and some polyphenols in positive ionization mode. These results suggest that CEFAC may present compounds with the ability to interact and act synergistically with antimicrobial drugs, highlighting its potential as an alternative source for the development of new antimicrobial agents.

The Pharmacological Activity, Biochemical Properties, and Pharmacokinetics of the Major Natural Polyphenolic Flavonoid: Quercetin

Flavonoids are a class of natural substances present in plants, fruits, vegetables, wine, bulbs, bark, stems, roots, and tea. Several attempts are being made to isolate such natural products, which are popular for their health benefits. Flavonoids are now seen as an essential component in a number of cosmetic, pharmaceutical, and medicinal formulations. Quercetin is the major polyphenolic flavonoid found in food products, including berries, apples, cauliflower, tea, cabbage, nuts, and onions that have traditionally been treated as anticancer and antiviral, and used for the treatment of allergic, metabolic, and inflammatory disorders, eye and cardiovascular diseases, and arthritis. Pharmacologically, quercetin has been examined against various microorganisms and parasites, including pathogenic bacteria, viruses, and Plasmodium, Babesia, and Theileria parasites. Additionally, it has shown beneficial effects against Alzheimer’s disease (AD), and this activity is due to its inhibitory effect against acetylcholinesterase. It has also been documented to possess antioxidant, antifungal, anti-carcinogenic, hepatoprotective, and cytotoxic activity. Quercetin has been documented to accumulate in the lungs, liver, kidneys, and small intestines, with lower levels seen in the brain, heart, and spleen, and it is extracted through the renal, fecal, and respiratory systems. The current review examines the pharmacokinetics, as well as the toxic and biological activities of quercetin.

Synergistic effects of ketamine and azole derivatives on Candida spp. resistance to fluconazole

The emergence of Candida spp. with resistance to antifungal molecules, mainly the azole class, is an increasing complication in hospitals around the globe. Aim: In the present research, we evaluated the synergistic effects of ketamine with two azole derivatives, itraconazole and fluconazole, on strains of Candida spp. to fluconazole. Materials & methods: The drug synergy was evaluated by quantifying the fractional inhibitory concentration index and by fluorescence microscopy and flow cytometry techniques. Results: Our achievements showed a synergistic effect between ketamine in addition to the two antifungal agents (fluconazole and itraconazole) against planktonic cells and biofilms of Candida spp. Conclusion: This combination promoted alteration of membrane integrity, generation of reactive oxygen species, damage to and DNA and externalization of phosphatidylserine.

Antifungal and Antivirulence Activities of Hydroalcoholic Extract and Fractions of Platonia insignis Leaves against Vaginal Isolates of Candida Species

Vulvovaginal candidiasis is a common fungal infection in women. In this study, Platonia insignis hydroalcoholic extract (PiHE) and its fractions were evaluated for antifungal and antivirulence activities against vaginal Candida species. Dichloromethane (DCMF) and ethyl acetate fractions (EAF) obtained from PiHE effectively inhibited the pathogen. Electrospray ionization mass spectrometry was used for identifying the main compounds in extracts. Minimal inhibitory and fungicidal concentrations (MIC and MFC, respectively) were determined by a broth microdilution assay. Furthermore, we evaluated the effect of the extract and fractions on the virulence properties of Candida albicans, and their cytotoxicity effect was determined on RAW 264.7 cells. Compounds found in extracts were flavonoid glycosides, mainly derivatives of quercetin and myricetin. Extracts showed antifungal potential, with the lowest MIC value for EAF (1.3 mg/mL) and inhibited Candida adherence and biofilm formation. EAF disrupted 48 h biofilms with an inhibition rate of more than 90%. The extract and its fractions exhibited no cytotoxicity. The antifungal effects were attributed to the ability of these extracts to alter the mitochondrial membrane potential for the release of pro-apoptotic factors in the cytosol. In conclusion, our data suggest that PiHE and EAF could act as novel candidates for the development of new therapeutic treatments against fungal infections.

In vitro Antibiotic and Modulatory Activity of Mesosphaerum suaveolens (L.) Kuntze against Candida strains

The emergence of fungal resistance to commercial drugs has been a major problem for the WHO. In this context, research with natural products is promising in the discovery of new active substances. Thus, this work evaluated the antifungal effect of a medicinal plant (i.e., Mesosphaerum suaveolens) against strains of the genus Candida, tested the combined effect with the drug fluconazole, and, finally, determined the phenolic constituents present in the species. Initially, aqueous extracts of leaves (AELMs) and aerial parts (AEAPMs) of the species were prepared. For microbiological assays, the minimum fungicidal concentration was determined by broth microdilution, and the combined effect of fluconazole extracts were verified by sub-inhibitory microdilution concentrations (CFM/8) followed by spectrophotometric readings which were used to determine the IC50. HPLC detected the presence of flavonoids and phenolic acids, detecting eight compounds present in the samples of which caffeic acid and quercetin were major components. The AELMs modulated fluconazole activity since it decreased fluconazole's IC50 from 7.8 µg/mL to an IC50 of 4.7 µg/mL (CA LM 77) and from 28.8 µg/mL to 18.26 µg/mL (CA INCQS 40006) for the C. albicans strains. The AEAPMs were able to potentiate the effect of fluconazole more effectively than the AELMs. Such an effect was significant for the 16 µg/mL concentration for CA LM 77 and 32 µg/mL for CA INCQS 40006. The AEAPMs as well as the AELMs presented clinically relevant activities for C. tropicalis strains. For the C. tropicalis LM 23 strain, the AEPMs obtained an IC50 of 25 µg/mL and the AELMs an IC50 of 359.9 µg/mL.

Anti-Fungal Efficacy and Mechanisms of Flavonoids

The prevalence of fungal infections is growing at an alarming pace and the pathogenesis is still not clearly understood. Recurrence of these fungal diseases is often due to their evolutionary avoidance of antifungal resistance. The development of suitable novel antimicrobial agents for fungal diseases continues to be a major problem in the current clinical field. Hence, it is urgently necessary to develop surrogate agents that are more effective than conventional available drugs. Among the remarkable innovations from earlier investigations on natural-drugs, flavonoids are a group of plant-derived substances capable of promoting many valuable effects on humans. The identification of flavonoids with possible antifungal effects at small concentrations or in synergistic combinations could help to overcome this problem. A combination of flavonoids with available drugs is an excellent approach to reduce the side effects and toxicity. This review focuses on various naturally occurring flavonoids and their antifungal activities, modes of action, and synergetic use in combination with conventional drugs.

Evaluation of the Antifungal Activity of the Licania Rigida Leaf Ethanolic Extract against Biofilms Formed by Candida Sp. Isolates in Acrylic Resin Discs

Candida sp. treatment has become a challenge due to the formation of biofilms which favor resistance to conventional antifungals, making the search for new compounds necessary. The objective of this study was to identify the composition of the Licania rigida Benth. leaf ethanolic extract and to verify its antifungal activity against Candida sp. and its biofilms. The composition identification was performed using the ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS/MS) technique. The antifungal activity of extract and fluconazole against planktonic cells and biofilms was verified through the minimum inhibitory concentration (MIC) following biofilm induction and quantification in acrylic resin discs by reducing tetrazolic salt, with all isolates forming biofilms within 48 h. Six constituents were identified in the extract, and the compounds identified are derivatives from phenolic compounds such as flavonoids (epi) gallocatechin Dimer, epigallocatechin and gallocatechin, Myricetin-O-hexoside, Myricitrin, and Quercetin-O-rhamnoside. The extract reduced biofilm formation in some of the strains analyzed, namely C. tropicalis URM5732, C. krusei INCQS40042, and C. krusei URM6352. This reduction was also observed in the treatment with fluconazole with some of the analyzed strains. The extract showed significant antifungal and anti-biofilm activities with some of the strains tested.

Exploration of Medicinal Plants as Sources of Novel Anticandidal Drugs

BACKGROUND

Human infections associated with skin and mucosal surfaces, mainly in tropical and sub-tropical parts of the world. During the last decade, there have been an increasing numbers of cases of fungal infections in immunocompromised patients, coupled with an increase in the number of incidences of drug resistance and toxicity to anti fungal agents. Hence, there is a dire need for safe, potent and affordable new antifungal drugs for the efficient management of candidal infections with minimum or no side effects.

INTRODUCTION

Candidiasis represents a critical problem to human health and a serious concern worldwide. Due to the development of drug resistance, there is a need for new antifungal agents. Therefore, we reviewed the different medicinal plants as sources of novel anticandidal drugs.

METHODS

The comprehensive and detailed literature on medicinal plants was carried out using different databases, such as Google Scholar, PubMed, and Science Direct and all the relevant information from the articles were analyzed and included.

RESULTS

Relevant Publications up to the end of November 2018, reporting anticandidal activity of medicinal plants has been included in the present review. In the present study, we have reviewed in the light of SAR and mechanisms of action of those plants whose extracts or phytomolecules are active against candida strains.

CONCLUSION

This article reviewed natural anticandidal drugs of plant origin and also summarized the potent antifungal bioactivity against fungal strains. Besides, mechanism of action of these potent active plant molecules was also explored for a comparative study. We concluded that the studied active plant molecules exhibit potential antifungal activity against resistant fungal strains.

Effects of the Natural Peptide Crotamine from a South American Rattlesnake on Candida auris, an Emergent Multidrug Antifungal Resistant Human Pathogen

Invasive Candida infections are an important growing medical concern and treatment options are limited to a few antifungal drug classes, with limited efficacies depending on the infecting organism. In this scenario, invasive infections caused by multiresistant Candida auris are emerging in several places around the world as important healthcare-associated infections. As antimicrobial peptides (AMPs) exert their activities primarily through mechanisms involving membrane disruption, they have a lower chance of inducing drug resistance than general chemical antimicrobials. Interestingly, we previously described the potent candicidal effect of a rattlesnake AMP, crotamine, against standard and treatment-resistant clinical isolates, with no hemolytic activity. We evaluated the antifungal susceptibility of several Candida spp. strains cultured from different patients by using the Clinical and Laboratory Standards Institute (CLSI) microdilution assay, and the antifungal activity of native crotamine was evaluated by a microbial growth inhibition microdilution assay. Although all Candida isolates evaluated here showed resistance to amphotericin B and fluconazole, crotamine (40–80 µM) exhibited in vitro activity against most isolates tested. We suggest that this native polypeptide from the South American rattlesnake Crotalus durissus terrificus has potential as a structural model for the generation of a new class of antimicrobial compounds with the power to fight against multiresistant Candida spp.

Anti-biofilm and cytoprotective activities of quercetin against Pseudomonas aeruginosa isolates

Increase in infection with multidrug resistant Pseudomonas aeruginosa is a serious global challenge in healthcare. Pseudomonas aeruginosa is capable of causing human infection in various sites and complicates the infection due to its virulence factors. This study was aimed to investigate the effect of quercetin, a dietary flavonoid against the virulence factors of P. aeruginosa and its cell protective effects on epithelial cells. Bactericidal activity, anti-biofilm activity and effect on different virulence factors were carried out using standard methods by using five P. aeruginosa isolates. Cytotoxicity and cell protective effect of quercetin was evaluated by trypan blue dye exclusion assay. All the tested isolates were completely inhibited (100%) by quercetin at a concentration of 500 μg ml^-1 . It showed significant (P < 0·05) inhibitory effect on virulence factors including biofilm formation and showed significant protective effect on HEK 293T cells infected with P. aeruginosa strains. This study supports the role of quercetin against P. aeruginosa, by inhibiting virulence factors as well as its cytoprotective activity during bacterial infection either by attenuating the virulence or providing direct protective effect to the host cells. SIGNIFICANCE AND IMPACT OF THE STUDY: The increase in infections caused by opportunistic pathogen Pseudomonas aeruginosa is a serious concern in the health care system. This study describes the beneficial effects of a dietary flavonoid, quercetin against pathogenic P. aeruginosa strains and its protective effect against the P. aeruginosa infection in HEK 293T cells in vitro.

Antifungal effects of the flavonoids kaempferol and quercetin: a possible alternative for the control of fungal biofilms

This study aimed to determine the minimum inhibitory concentration (MIC) of kaempferol and quercetin against planktonic and biofilm forms of the Candida parapsilosis complex. Initially, nine C. parapsilosis sensu stricto, nine C. orthopsilosis and nine C. metapsilosis strains were used. Planktonic susceptibility to kaempferol and quercetin was assessed. Growing and mature biofilms were then exposed to the flavonoids at MIC or 10xMIC, respectively, and theywere also analyzed by confocal laser scanning microscopy. The MIC ranges were 32-128 µg ml^-1 for kaempferol and 0.5-16 µg ml^-1 for quercetin. Kaempferol and quercetin decreased (P < 0.05) the metabolic activity and biomass of growing biofilms of the C. parapsilosis complex. As for mature biofilms, the metabolic effects of the flavonoids varied, according to the cryptic species, but kaempferol caused an overall reduction in biofilm biomass. Microscopic analyses showed restructuring of biofilms after flavonoid exposure. These results highlight the potential use of these compounds as sustainable resources for the control of fungal biofilms.