Synergistic effects of tea catechin epigallocatechin gallate and antimycotics against oral Candida species

Identification of chicken-derived antibodies targeting the Candida albicans Als3 protein

Candida albicans is a major opportunistic pathogen, responsible for nearly half of clinical candidemia cases. The rising prevalence of azole-resistant Candida species represents a significant clinical challenge, underscoring the urgent need for alternative therapeutic strategies. Monoclonal antibody-based therapies have emerged as a promising and cost-effective approach to combating Candida infections. Agglutinin-like sequence protein 3 (Als3), a key cell surface protein of C. albicans, plays a pivotal role in adherence and biofilm formation, both of which are essential for its pathogenesis. In this study, recombinant Als3 protein was purified and utilized to immunize chickens, resulting in the production of Als3-specific immunoglobulin Y (IgY) antibodies. Two single-chain variable fragment (scFv) antibody libraries were subsequently constructed using phage display technology, yielding transformant counts of 5.3 × 107 and 2.8 × 107, respectively. Phage-based enzyme-linked immunosorbent assay (ELISA) revealed enhanced signals following bio-panning, enabling the identification and sequence validation of three scFv antibodies. These scFv antibodies exhibited strong binding activities to Als3, as confirmed through ELISA and western blot analyses. Binding affinities were determined to be ~ 10⁻⁸ M via serial titration ELISA and competitive ELISA. Additionally, the selected scFv antibodies specifically recognized endogenous Als3 protein in C. albicans, as demonstrated by western blot and cell-based ELISA assays. In conclusion, this study successfully generated and characterized high-affinity scFv antibodies targeting Als3, which exhibited exceptional specificity and binding activity. These findings highlight their potential as promising immunotherapeutic candidates for the treatment of C. albicans infections. KEY POINTS: • The Als3 protein of C. albicans is a critical biomarker and therapeutic target • Chicken-derived scFv antibodies against Als3 were developed via phage display • The scFv antibodies showed strong binding to endogenous Als3 in C. albicans.

The regulation of auxin receptor gene CsAFB2 by csn-miR393a confers resistance against Colletotrichum gloeosporioides in tea plants

Anthracnose, a severe disease caused by Colletotrichum, affects diverse crops and leads to significant economic losses through pronounced fruit/leaf lesions. MicroRNAs (miRNAs) play crucial roles in modulating gene expression in response to disease resistance, defence responses and plant immunity. However, the regulatory mechanisms of miRNAs in responses to Colletotrichum gloeosporioides remain unknown in tea plants. Our study revealed that csn-miR393a targets auxin receptor gene CsAFB2 during resistance to C. gloeosporioides in tea plants by comparing the resistant cultivar Zhongcha108 to the susceptible cultivar Longjing43. Through Nicotiana benthamiana leaf co-transformation assays, we demonstrated that csn-miR393a suppresses the expression of CsAFB2, and csn-miR393a target mimic blocks the function of csn-miR393a, leading to increase in the expression of CsAFB2. Repression of transcripts in tea leaves by antisense oligonucleotides demonstrated that csn-miR393a negatively affects the tea plant defence by regulating reactive oxygen species homoeostasis, PR gene expression and catechin accumulation. To further validate the regulatory mechanisms of csn-miR393a, we developed transgenic tea plants overexpressing CsAFB2, resulting in enhanced resistance responses against C. gloeosporioides. Additionally, transgenic N. benthamiana lines overexpressing a csn-miR393a target mimic provided further evidence that csn-miR393a negatively regulates the tea plant defence response against C. gloeosporioides by suppressing CsAFB2. Therefore, manipulating csn-miR393a or its target gene, CsAFB2, has the potential to strengthen the tea plant's resistance against tea anthracnose.

Active biodegradable bacterial cellulose films with potential to minimize the plastic pollution: Preparation, antibacterial application, and mechanism

Petroleum-based films have triggered a serious global pollution crisis because they are difficult to recycle, degrade, and reuse. Developing alternative sustainable active films represents a powerful strategy to address these issues. Here, a multifunctional biodegradable bacterial cellulose (BC) film incorporated with guanidine-based polymer (PHGH)/gallic acid (GA) was constructed (termed OBC-PHGH/GA). The resulting OBC-PHGH/GA film exhibited a highly interweaved nanofiber network structure with excellent tensile strength and ductility. The OBC-PHGH/GA film showed an excellent antibacterial effect against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) with inhibition efficiencies of ∼99.99 % compared with the OBC film. Moreover, the as-prepared film showed excellent UV-shielding, antioxidant, and antifungal activities, showing great potential in food packaging. More importantly, the OBC-PHGH/GA film can be degraded into safe and reusable sugars, demonstrating outstanding environmental friendliness and sustainability. This work provides a promising and unique strategy for designing and fabricating green active packaging materials.

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.

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.

Synergistic Effect of Plant Compounds in Combination with Conventional Antimicrobials against Biofilm of Staphylococcus aureus, Pseudomonas aeruginosa, and Candida spp

Bacterial and fungal biofilm has increased antibiotic resistance and plays an essential role in many persistent diseases. Biofilm-associated chronic infections are difficult to treat and reduce the efficacy of medical devices. This global problem has prompted extensive research to find alternative strategies to fight microbial chronic infections. Plant bioactive metabolites with antibiofilm activity are known to be potential resources to alleviate this problem. The phytochemical screening of some medicinal plants showed different active groups, such as stilbenes, tannins, alkaloids, terpenes, polyphenolics, flavonoids, lignans, quinones, and coumarins. Synergistic effects can be observed in the interaction between plant compounds and conventional drugs. This review analyses and summarises the current knowledge on the synergistic effects of plant metabolites in combination with conventional antimicrobials against biofilms of Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans. The synergism of conventional antimicrobials with plant compounds can modify and inhibit the mechanisms of acquired resistance, reduce undesirable effects, and obtain an appropriate therapeutic effect at lower doses. A deeper knowledge of these combinations and of their possible antibiofilm targets is needed to develop next-generation novel antimicrobials and/or improve current antimicrobials to fight drug-resistant infections attributed to biofilm.

Chitosan hydrogel modified with lanthanum as a drug delivery system for epigallocatechin gallate: Investigation of hydrogel - drug interaction by FT-IR and Raman spectroscopy

In the presented work, chitosan hydrogel modified with lanthanum was obtained for the first time. The hydrogel was used as a carrier in the controlled release of epigallocatechin gallate. The work proved the effectiveness of drug sorption by hydrogel and controlled release in simulated body fluids. The drug was released slowly and in a controlled manner from the carrier. The research techniques used in this work (FT-IR spectroscopy and imaging, Raman spectroscopy, SEM/EDS) allowed to confirm the successful retention of EGCG on the hydrogel surface. On the basis of the EDS mapping, it was possible to confirm the even distribution of the lanthanum ions. Using FT-IR imaging, we verified that the drug was evenly distributed on the entire surface of the prepared material. The antifungal effectiveness of the material has been proven on several types of fungi. The research proved that the prepared material is capable of long-term release of the active substance and has antifungal properties. As a result, the prepared material can be successfully used as an implantable hydrogel or a coating in, e.g. titanium implants.

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.

The role of catechin in electroporation of pancreatic cancer cells - Effects on pore formation and multidrug resistance proteins

Catechin is a bioflavonoid known for its anti-cancer properties. In the present study, we combined theoretical and experimental approaches to reveal the potential of catechin application in the electroporation (EP) or electrochemotherapy (ECT) of pancreatic cancer cells. The molecular dynamics simulations were implemented to examine the interactions of catechin with a model of a membrane, its influence on the membrane's thickness, and the impact of the catechin-membrane interaction on the pore formation. The data were confronted with experimental measurement of the threshold electric field required for permeabilization of pancreatic cancer cells to a fluorescent dye YO-PRO-1. Further, we examined the influence of catechin on cell viability following electroporation with cisplatin or calcium ions. Finally, we investigated the catechin impact on four proteins associated with multidrug resistance: P-glycoprotein, MRP1, BCRP, and LRP. We demonstrated that catechin may boost the effects of electroporation through various mechanisms: i) increasing the cell permeability prior to electroporation ii) increasing the electroporation threshold iii) sensitization of cells to chemotherapeutic compounds. We showed that catechin incubation influences mRNA levels and mitigates the immunoreactivity of Pgp, MRP1, BCRP, and LRP but these changes did not translate to the efficacy of electrochemotherapy.

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.

Natural Compounds: A Hopeful Promise as an Antibiofilm Agent Against Candida Species

The biofilm communities of Candida are resistant to various antifungal treatments. The ability of Candida to form biofilms on abiotic and biotic surfaces is considered one of the most important virulence factors of these fungi. Extracellular DNA and exopolysaccharides can lower the antifungal penetration to the deeper layers of the biofilms, which is a serious concern supported by the emergence of azole-resistant isolates and Candida strains with decreased antifungal susceptibility. Since the biofilms' resistance to common antifungal drugs has become more widespread in recent years, more investigations should be performed to develop novel, inexpensive, non-toxic, and effective treatment approaches for controlling biofilm-associated infections. Scientists have used various natural compounds for inhibiting and degrading Candida biofilms. Curcumin, cinnamaldehyde, eugenol, carvacrol, thymol, terpinen-4-ol, linalool, geraniol, cineole, saponin, camphor, borneol, camphene, carnosol, citronellol, coumarin, epigallocatechin gallate, eucalyptol, limonene, menthol, piperine, saponin, α-terpineol, β-pinene, and citral are the major natural compounds that have been used widely for the inhibition and destruction of Candida biofilms. These compounds suppress not only fungal adhesion and biofilm formation but also destroy mature biofilm communities of Candida. Additionally, these natural compounds interact with various cellular processes of Candida, such as ABC-transported mediated drug transport, cell cycle progression, mitochondrial activity, and ergosterol, chitin, and glucan biosynthesis. The use of various drug delivery platforms can enhance the antibiofilm efficacy of natural compounds. Therefore, these drug delivery platforms should be considered as potential candidates for coating catheters and other medical material surfaces. A future goal will be to develop natural compounds as antibiofilm agents that can be used to treat infections by multi-drug-resistant Candida biofilms. Since exact interactions of natural compounds and biofilm structures have not been elucidated, further in vitro toxicology and animal experiments are required. In this article, we have discussed various aspects of natural compound usage for inhibition and destruction of Candida biofilms, along with the methods and procedures that have been used for improving the efficacy of these compounds.

The antimicrobial and immunomodulatory effects of Ionophores for the treatment of human infection

Ionophores are a diverse class of synthetic and naturally occurring ion transporter compounds which demonstrate both direct and in-direct antimicrobial properties against a broad panel of bacterial, fungal, viral and parasitic pathogens. In addition, ionophores can regulate the host-immune response during communicable and non-communicable disease states. Although the clinical use of ionophores such as Amphotericin B, Bedaquiline and Ivermectin highlight the utility of ionophores in modern medicine, for many other ionophore compounds issues surrounding toxicity, bioavailability or lack of in vivo efficacy studies have hindered clinical development. The antimicrobial and immunomodulating properties of a range of compounds with characteristics of ionophores remain largely unexplored. As such, ionophores remain a latent therapeutic avenue to address both the global burden of antimicrobial resistance, and the unmet clinical need for new antimicrobial therapies. This review will provide an overview of the broad-spectrum antimicrobial and immunomodulatory properties of ionophores, and their potential uses in clinical medicine for combatting infection.

Synergistic effect of thymoquinone and nystatin in the treatment of oral candidiasis; an in vitro study

The effectiveness of antifungal agents may be insufficient against resistant strains in some cases of oral candidiasis. The aim of this study was to evaluate the antifungal effect of thymoquinone against Candidaalbicans, Candidatropicalis, Candidaglabrata and Candidakrusei strains and the synergistic antifungal activity of these strains in combination with nystatin. To evaluate in vitro antifungal activity and interactions between thymoquinone and nystatin, substances were tested against Candidaalbicans ATCC 10,231, C.tropicalis ATCC 750, C.krusei ATCC 6258 and C.glabrata ATCC 2001 standard strains both individually and combinationally via microdilution method. MIC and ΣFIC index value were analysed. The Kruskal Wallis test and Bonferroni test were used for statistical evaluations. Statistical significance was set at p < 0.05. A statistically significant difference was observed between the mean ranks of all Candida species and doses of thymoquinone, nystatin, and the combination thymoquinone-nystatin (p < 0.05). MIC values for thymoquinone were determined as 15 μg/mL for C.albicans, C.tropicalis and C.krusei while it was 30 μg/mL for C.glabrata. Moreover, MIC for nystatin was found as 1.875 μg/mL for C.albicans, C.tropicalis and C.krusei, whereas it was 7.5 μg/mL in C. glabrata. Interaction assays and ΣFIC index value revealed that, TQ and nystatin have a synergistic effect against to all strains. Thymoquinone was found to have antifungal activity on Candida species and synergistic effect when combined with nystatin.

Antifungal Activity of the Phenolic Compounds Ellagic Acid (EA) and Caffeic Acid Phenethyl Ester (CAPE) against Drug-Resistant Candida auris

Candida auris is an emerging healthcare-associated fungal pathogen that has become a serious global health threat. Current treatment options are limited due to drug resistance. New therapeutic strategies are required to target this organism and its pathogenicity. Plant polyphenols are structurally diverse compounds that present a vast range of biological properties. In the present study, plant-derived molecules ellagic acid (EA) and caffeic acid phenethyl ester (CAPE) were investigated for their antifungal and antivirulence activities against Candida auris. We also tested against C. albicans. The minimum inhibitory concentration (MIC) for EA ranged from 0.125 to 0.25 µg/mL and for CAPE ranged from 1 to 64 µg/mL against drug-resistant C. auris strains. Killing kinetics determined that after 4 h treatment with CAPE, there was a complete reduction of viable C. auris cells compared to fluconazole. Both compounds might act by modifying the fungal cell wall. CAPE significantly reduced the biomass and the metabolic activity of C. auris biofilm and impaired C. auris adhesion to cultured human epithelial cells. Furthermore, both compounds prolonged the survival rate of Galleria mellonella infected by C. auris (p = 0.0088 for EA at 32 mg/kg and p = 0.0028 for CAPE at 4 mg/kg). In addition, EA at 4 μg/mL prolonged the survival of C. albicans-infected Caenorhabditis elegans (p < 0.0001). CAPE was not able to prolong the survival of C. albicans-infected C. elegans. These findings highlight the antifungal and antivirulence effects of EA and CAPE against C. auris, and warrant further investigation as novel antifungal agents against drug-resistant infections.

Dual-targeted carbon-dot-drugs nanoassemblies for modulating Alzheimer's related amyloid-β aggregation and inhibiting fungal infection

Amyloid aggregation and fungal infection, especially amyloid beta (Aβ) peptide and Candida albicans are considered as two of the crucial pathogenic agents in Alzheimer's disease (AD). In this work, we propose an innovative treatment strategy for AD, targeting at not only Aβ aggregation but also Candida albicans infection. Here, a high-performance nanomaterial, namely gCDs-E, have been prepared by self-assembled of glycosylated carbon dots (gCDs) and epigallocatechin-3-gallate (EGCG). Surprisingly, gCDs-E can not only suppress the fibrillation of Aβ and disaggregate Aβ fibrils, but also effectively inhibit the activity of Candida albicans. More importantly, the prepared gCDs-E can effectively cut down the cytotoxicity of amyloid aggregations, and the cell viability reached to 99.2%. In addition, the capability of the gCDs-E for blood brain barrier (BBB) penetration was also observed using a normal mice model. Above all, the gCDs-E greatly cleaned Aβ deposition and improved memory impairment in APP/PS1 transgenic AD model mice, confirming its potential as therapeutic agent for AD treatment.

Role of agglutinin-like sequence protein 3 (Als3) in the structure and antifungal resistance of Candida albicans biofilms

Agglutinin-like sequence protein 3 (Als3) is a cell surface glycoprotein of Candida albicans that plays essential roles in the processes of adherence and biofilm formation in vitro. In this study, we focused on the contribution of Als3 to the structure and drug susceptibility of biofilms. The C. albicans wild-type (WT) strain DAY185, the als3Δ/Δ null strain and the als3Δ/Δ + pALS3 complemented strain were used. Colony-forming unit enumeration, crystal violet and cell surface hydrophobicity assays, scanning electron microscopy and confocal laser scanning microscopy coupled with analyses using COMSTAT software were performed to evaluate the biomass and architecture of the biofilms. The detailed architectural analysis showed a significant variation in the biofilm parameters of the als3Δ/Δ biofilms compared with those of the WT biofilms. Fluconazole, miconazole and amphotericin B were selected as the antifungal agents for the antimycotic susceptibility test, and increased susceptibility was found with the ALS3 deletion biofilms. A quantitative real-time polymerase chain reaction analysis showed downregulation of biofilm formation-related genes (ALS1, EFG1, HWP1 and CSH1) and drug resistance-related genes (ERG11, CDR1, CDR2 and MDR1) in the als3Δ/Δ biofilms. We concluded that Als3 contributes to biofilm formation by changing the biofilm architecture and is involved in the antifungal resistance of C. albicans biofilms.

Catechins as Model Bioactive Compounds for Biomedical Applications

Research regarding polyphenols has gained prominence over the years because of their potential as pharmacological nutrients. Most polyphenols are flavanols, commonly known as catechins, which are present in high amounts in green tea. Catechins are promising candidates in the field of biomedicine. The health benefits of catechins, notably their antioxidant effects, are related to their chemical structure and the total number of hydroxyl groups. In addition, catechins possess strong activities against several pathogens, including bacteria, viruses, parasites, and fungi. One major limitation of these compounds is low bioavailability. Catechins are poorly absorbed by intestinal barriers. Some protective mechanisms may be required to maintain or even increase the stability and bioavailability of these molecules within living organisms. Moreover, novel delivery systems, such as scaffolds, fibers, sponges, and capsules, have been proposed. This review focuses on the unique structures and bioactive properties of catechins and their role in inflammatory responses as well as provides a perspective on their use in future human health applications.

Pathogenesis and Clinical Relevance of Candida Biofilms in Vulvovaginal Candidiasis

The ability of Candida spp. to form biofilms is crucial for its pathogenicity, and thus, it should be considered an important virulence factor in vulvovaginal candidiasis (VVC) and recurrent VVC (RVVC). Its ability to generate biofilms is multifactorial and is generally believed to depend on the site of infection, species and strain involved, and the microenvironment in which the infection develops. Therefore, both cell surface proteins, such as Hwp1, Als1, and Als2, and the cell wall-related protein, Sun41, play a critical role in the adhesion and virulence of the biofilm. Immunological and pharmacological approaches have identified the NLRP3 inflammasome as a crucial molecular factor contributing to host immunopathology. In this context, we have earlier shown that Candida albicans associated with hyphae-secreted aspartyl proteinases (specifically SAP4-6) contribute to the immunopathology of the disease. Transcriptome profiling has revealed that non-coding transcripts regulate protein synthesis post-transcriptionally, which is important for the growth of Candida spp. Other studies have employed RNA sequencing to identify differences in the 1,245 Candida genes involved in surface and invasive cellular metabolism regulation. In vitro systems allow the simultaneous processing of a large number of samples, making them an ideal screening technique for estimating various physicochemical parameters, testing the activity of antimicrobial agents, and analyzing genes involved in biofilm formation and regulation (in situ) in specific strains. Murine VVC models are used to study C. albicans infection, especially in trials of novel treatments and to understand the cause(s) for resistance to conventional therapeutics. This review on the clinical relevance of Candida biofilms in VVC focuses on important advances in its genomics, transcriptomics, and proteomics. Moreover, recent experiments on the influence of biofilm formation on VVC or RVVC pathogenesis in laboratory animals have been discussed. A clear elucidation of one of the pathogenesis mechanisms employed by Candida biofilms in vulvovaginal candidiasis and its applications in clinical practice represents the most significant contribution of this manuscript.

Antifungal effect of tea extracts on Candida albicans

Determining whether tea extracts are effective in removing Candida albicans (C. albicans) from dentures is of interest. This study aimed to investigate the antifungal effect of tea extracts on C. albicans. One green tea (Anji white tea, AGW) and 2 oolong teas (Tie Guan Yin, TGY; Da Hong Pao, DHP) of different concentrations were tested. C. albicans suspensions were inoculated on the plates and the numbers of colony-forming units (CFU) in the culture medium were used to screen for the optimum tea extracts. Polymethyl methacrylate (PMMA) specimens that contained C. albicans biofilms were then treated with the tea extracts and the numbers of CFU were counted. The antifungal activities of the tea extracts were not significantly correlated with their catechin concentrations. Although AGW at 10.0 mg/mL and DHP at 2.5 mg/mL significantly inhibited C. albicans in the culture medium, the extracts failed to exert inhibitory effects against C. albicans biofilms on the PMMA surfaces.

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.

Looking for New Antifungal Drugs from Flavonoids: Impact of the Genetic Diversity of Candida albicans on the in-vitro Response

BACKGROUND

In an era in which antimicrobial resistance is increasing at an alarming pace, it is very important to find new antimicrobial agents effective against pathogenic microrganisms resistant to traditional treatments. Among the notable breakthroughs in the past years of research in natural-drug discovery, there is the identification and testing of flavonoids, a group of plant-derived substances capable of promoting many beneficial effects on humans. These compounds show different biological activities such as inhibition of neuroinflammation and tumor growth as well as antimicrobial activity against many microbial pathogens.

METHODS

We undertook a review of protocols and standard strains used in studies reporting the inhibitory effects of flavonoids against Candida albicans by focusing our attention on genetic characterization of the strains examined. Moreover, using the C. albicans MLST-database, we performed a phylogenetic analysis showing the genetic variation occurring in this species.

RESULTS

Today, we have enough information to estimate genetic diversity within microbial species and recent data revealed that most of fungal pathogens show complex population structures in which not a single isolate can be designated as representative of the entire taxon. This is especially true for the highly divergent fungal pathogen C. albicans, in which the assumption that one or few "standard strains" can represent the whole species is overly unrealistic and should be laid to rest.

CONCLUSION

The goal of this article is to shed light on the extent of genetic variation in C. albicans and how this phenomenon can largely influence the activity of flavonoids against this species.

Promising Alternative Therapeutics for Oral Candidiasis

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Candida is the main human fungal pathogen causing infections (candidiasis), mostly in the elderly and immunocompromised hosts. Even though Candida spp. is a member of the oral microbiota in symbiosis, in some circumstances, it can cause microbial imbalance leading to dysbiosis, resulting in oral diseases. Alternative therapies are urgently needed to treat oral candidiasis (usually associated to biofilms), as several antifungal drugs’ activity has been compromised. This has occurred especially due to an increasing occurrence of drugresistant in Candida spp. strains. The overuse of antifungal medications, systemic toxicity, cross-reactivity with other drugs and a presently low number of drug molecules with antifungal activity, have contributed to important clinical limitations.

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We undertook a structured search of bibliographic databases (PubMed Central, Elsevier’s ScienceDirect, SCOPUS and Springer’s SpringerLink) for peer-reviewed research literature using a focused review in the areas of alternatives to manage oral candidiasis. The keywords used were “candidiasis”, “oral candidiasis”, “biofilm + candida”, “alternative treatment”, “combination therapy + candida” and the reports from the last 10 to 15 years were considered for this review.

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This review identified several promising new approaches in the treatment of oral candidiasis: combination anti-Candida therapies, denture cleansers, mouth rinses as alternatives for disrupting candidal biofilms, natural compounds (e.g. honey, probiotics, plant extracts and essential oils) and photodynamic therapy.

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The findings of this review confirm the importance and the urgency of the development of efficacious therapies for oral candidal infections.

Plant-Derived Bioactives in Oral Mucosal Lesions: A Key Emphasis to Curcumin, Lycopene, Chamomile, Aloe vera, Green Tea and Coffee Properties

Oral mucosal lesions have many etiologies, including viral or bacterial infections, local trauma or irritation, systemic disorders, and even excessive alcohol and tobacco consumption. Folk knowledge on medicinal plants and phytochemicals in the treatment of oral mucosal lesions has gained special attention among the scientific community. Thus, this review aims to provide a brief overview on the traditional knowledge of plants in the treatment of oral mucosal lesions. This review was carried out consulting reports between 2008 and 2018 of PubMed (Medline), Web of Science, Embase, Scopus, Cochrane Database, Science Direct, and Google Scholar. The chosen keywords were plant, phytochemical, oral mucosa, leukoplakia, oral lichen planus and oral health. A special emphasis was given to certain plants (e.g., chamomile, Aloe vera, green tea, and coffea) and plant-derived bioactives (e.g., curcumin, lycopene) with anti-oral mucosal lesion activity. Finally, preclinical (in vitro and in vivo) and clinical studies examining both the safety and efficacy of medicinal plants and their derived phytochemicals were also carefully addressed.

Synergistic effects of tea polyphenol epigallocatechin 3-O-gallate and azole drugs against oral Candida isolates

BACKGROUND

The antifungal drug resistance has become an emerging problem in the management of candida infections worldwide. The objective of this study was to examine the efficacy of epigallocatechin 3-O-gallate (EGCG) alone and in combination with fluconazole/ketoconazole drugs against oral Candida isolates.

METHODS

Minimum inhibitory concentration (MIC) and minimum fungicidal concentrations (MFC) of EGCG against 60 oral Candida isolates and 4 ATCC strains were determined. Synergism of EGCG with azole drugs was evaluated by checkerboard micro-dilution method and calculated fractional inhibitory concentration index (FICI). Candida cells' ultrastructure was studied by electron microscopy.

RESULTS

MIC and MFC values of EGCG were in the range of 3.91-15.63 and 15.63-31.25μg/mL, respectively. Minimum biofilm inhibitory concentration (MBIC) range of EGCG (62.5-125μg/mL), was less than the ketoconazole (64-256μg/mL) and fluconazole (128-512μg/mL). The combination of EGCG with fluconazole/ketoconazole exhibited synergistic effects (ΣFICI≤0.50). EGCG with azole drugs showed high sensitivity against the tested isolates in growth curve assays. Against the biofilm, the susceptibility of fluconazole/ketoconazole significantly increased (3 to 5 fold), after combination with EGCG (MBIC/4) (P≤0.001). Electron microscopy of EGCG treated cells showed deformation of cell structure, ruptured cell wall and release of intracellular content. In molecular docking experiments, a strong interaction was observed between EGCG and fungal cell membrane molecule ergosterol.

CONCLUSION

We conclude that EGCG synergistically enhanced the antifungal potential of azole drugs. The synergistic potential of EGCG might be helpful in preventing the development of drug resistance, in lowering the drug dosage, and thus minimizing adverse effects.

Novel Approaches to the Control of Oral Microbial Biofilms

Effective management of biofilm-related oral infectious diseases is a global challenge. Oral biofilm presents increased resistance to antimicrobial agents and elevated virulence compared with planktonic bacteria. Antimicrobial agents, such as chlorhexidine, have proven effective in the disruption/inhibition of oral biofilm. However, the challenge of precisely and continuously eliminating the specific pathogens without disturbing the microbial ecology still exists, which is a major factor in determining the virulence of a multispecies microbial consortium and the consequent development of oral infectious diseases. Therefore, several novel approaches are being developed to inhibit biofilm virulence without necessarily inducing microbial dysbiosis of the oral cavity. Nanoparticles, such as pH-responsive enzyme-mimic nanoparticles, have been developed to specifically target the acidic niches within the oral biofilm where tooth demineralization readily occurs, in effect controlling dental caries. Quaternary ammonium salts (QAS) such as dimethylaminododecyl methacrylate (DMADDM), when incorporated into dental adhesives or resin composite, have also shown excellent and durable antimicrobial activity and thus could effectively inhibit the occurrence of secondary caries. In addition, custom-designed small molecules, natural products and their derivatives, as well as basic amino acids such as arginine, have demonstrated ecological effects by modulating the virulence of the oral biofilm without universally killing the commensal bacteria, indicating a promising approach to the management of oral infectious diseases such as dental caries and periodontal diseases. This article aims to introduce these novel approaches that have shown potential in the control of oral biofilm. These methods may be utilized in the near future to effectively promote the clinical management of oral infectious diseases and thus benefit oral health.

Green Tea Catechins: Their Use in Treating and Preventing Infectious Diseases

Green tea is one of the most popular drinks consumed worldwide. Produced mainly in Asian countries from the leaves of the Camellia sinensis plant, the potential health benefits have been widely studied. Recently, researchers have studied the ability of green tea to eradicate infectious agents and the ability to actually prevent infections. The important components in green tea that show antimicrobial properties are the catechins. The four main catechins that occur in green tea are (-)-epicatechin (EC), (-)-epicatechin-3-gallate (ECG), (-)-epigallocatechin (EGC), and (-)-epigallocatechin-3-gallate (EGCG). Of these catechins, EGCG and EGC are found in the highest amounts in green tea and have been the subject of most of the studies. These catechins have been shown to demonstrate a variety of antimicrobial properties, both to organisms affected and in mechanisms used. Consumption of green tea has been shown to distribute these compounds and/or their metabolites throughout the body, which allows for not only the possibility of treatment of infections but also the prevention of infections.

Growth Media Affect Assessment of Antimicrobial Activity of Plant-Derived Polyphenols

This study aimed to investigate the effects of different microbial growth media on the laboratory assessment of antimicrobial activity of natural polyphenolic compounds. The inhibition of the tea polyphenol EGCG on growth of selected oral microorganisms was evaluated in complex media and a protein-free chemically defined medium (CDM). Other antimicrobial agents (polyphenolic grape seed extract, plant alkaloid berberine, methyl salicylate, and chlorhexidine gluconate) were also tested in the study. The presence of proteins and their effects on the antimicrobial activity of EGCG were investigated by the addition of BSA to the CDM. The MICs of EGCG against test oral microorganisms were 4 to 64 times higher in complex media than in CDM. The polyphenolic grape seed extract exhibited similar discrepancies. However, the MICs of the nonpolyphenolic compounds (berberine, methyl salicylate, and chlorhexidine) were not significantly different between the two growth media. The MIC of EGCG against S. mutans UA159 in CDM with added BSA was 16 times higher than that in CDM alone. Therefore, nonproteinaceous CDM should be used to avoid interference of proteins with the active ingredients when testing the antimicrobial activity of plant-derived polyphenolic compounds against microorganisms. This will also minimize the discrepancies noted in results obtained by different investigators.

Plant phenolics and terpenoids as adjuvants of antibacterial and antifungal drugs

BACKGROUND

The intensive use of antibacterial and antifungal drugs has dramatically increased the microbial resistance and has led to a higher number of difficult-to-eradicate infections. Combination therapy with two or more antimicrobial drugs has emerged some years ago to overcome the issue, but it has proven to be not completely effective. Natural secondary metabolites of MW ≤ 500 represent promising adjuvants for antimicrobials and have been the object of several researches that have increased in the last two decades.

PURPOSE

The purpose of this Review is to do a literature search of the natural compounds that showed high enhancing capacity of antibacterials' and antifungals' effects against planktonic bacteria and fungi and to analyze which are the natural products most used in combination with a focus on polyphenols and terpenoids.

RESULTS

One hundred of papers were collected for reviewing. Fifty six (56) of them deal with combinations of low MW natural products with antibacterial drugs against planktonic bacteria and forty four (44) on natural products with antifungal drugs against planktonic fungi. Of the antibacterial adjuvants, 41 (73%) were either polyphenols (27; 48%) or terpenes (14; 25%). The remaining 15 papers (27%), deal with different class of natural products. Since most natural potentiators belong to the terpene or phenolic structural types, a more detailed description of the works dealing with these type of compounds is provided here. Bacterial and fungal resistance mechanisms, the modes of action of the main classes of antibacterial and antifungal drugs and the methodologies most used to assess the type of interactions in the combinations were included in the Review too.

CONCLUSIONS AND PERSPECTIVES

Several promising results on the potentiation effects of antifungals' and antibacterials' activities by low MW natural products mainly on polyphenols and terpenes were reported in the literature and, in spite of that most works included only in vitro assays, this knowledge opens a wide range of possibilities for the combination antimicrobial therapy. Further research including in vivo assays and clinical trials are required to determine the relevance of these antimicrobial enhancers in the clinical area and should be the focus of future studies in order to develop new antimicrobial combination agents that overpass the drawbacks of the existing antibiotics and antifungals in clinical use.

The synergistic potential of various teas, herbs and therapeutic drugs in health improvement: a review

Tea is one of the most widely consumed non-alcoholic beverages in the world next to water. It is classified as Camellia sinensis and non-Camellia sinensis (herbal teas). The common bioactive compounds found mainly in green teas are flavan-3-ols (catechins) (also called flavanols), proanthocyanidins (tannins) and flavonols. Black tea contains theaflavins and thearubigins and white tea contains l-theanine and gamma-aminobutyric acid (GABA), while herbal teas contain diverse polyphenols. Phytochemicals in tea exhibit antimicrobial, anti-diabetic and anti-cancer activities that are perceived to be helpful in managing chronic diseases linked to lifestyle. Many of these phytochemicals are reported to be biologically active when combined. Knowledge of the synergistic interactions of tea with other teas or herbs in terms of biological activities will be of benefit for therapeutic enhancement. There is evidence that various types of teas act synergistically in exhibiting health benefits to humans, improving consumer acceptance and economic value. Similar observations have been made when teas and herbs or medicinal drugs were combined. The aim of this review is to highlight potential beneficial synergies between combinations of different types of teas, tea and herbs, and tea and medicinal drugs. © 2017 Society of Chemical Industry.

Candida glabrata Biofilms: How Far Have We Come?

Infections caused by Candida species have been increasing in the last decades and can result in local or systemic infections, with high morbidity and mortality. After Candida albicans, Candida glabrata is one of the most prevalent pathogenic fungi in humans. In addition to the high antifungal drugs resistance and inability to form hyphae or secret hydrolases, C. glabrata retain many virulence factors that contribute to its extreme aggressiveness and result in a low therapeutic response and serious recurrent candidiasis, particularly biofilm formation ability. For their extraordinary organization, especially regarding the complex structure of the matrix, biofilms are very resistant to antifungal treatments. Thus, new approaches to the treatment of C. glabrata's biofilms are emerging. In this article, the knowledge available on C. glabrata's resistance will be highlighted, with a special focus on biofilms, as well as new therapeutic alternatives to control them.

Biofilm formation of the black yeast-like fungus Exophiala dermatitidis and its susceptibility to antiinfective agents

Various fungi have the ability to colonize surfaces and to form biofilms. Fungal biofilm-associated infections are frequently refractory to targeted treatment because of resistance to antifungal drugs. One fungus that frequently colonises the respiratory tract of cystic fibrosis (CF) patients is the opportunistic black yeast-like fungus Exophiala dermatitidis. We investigated the biofilm-forming ability of E. dermatitidis and its susceptibility to various antiinfective agents and natural compounds. We tested 58 E. dermatitidis isolates with a biofilm assay based on crystal violet staining. In addition, we used three isolates to examine the antibiofilm activity of voriconazole, micafungin, colistin, farnesol, and the plant derivatives 1,2,3,4,6-penta-O-galloyl-b-D-glucopyranose (PGG) and epigallocatechin-3-gallate (EGCG) with an XTT reduction assay. We analysed the effect of the agents on cell to surface adhesion, biofilm formation, and the mature biofilm. The biofilms were also investigated by confocal laser scan microscopy. We found that E. dermatitidis builds biofilm in a strain-specific manner. Invasive E. dermatitidis isolates form most biomass in biofilm. The antiinfective agents and the natural compounds exhibited poor antibiofilm activity. The greatest impact of the compounds was detected when they were added prior cell adhesion. These findings suggest that prevention may be more effective than treatment of biofilm-associated E. dermatitidis infections.

Antifungal effects of phytocompounds on Candida species alone and in combination with fluconazole

Invasive fungal infections caused by Candida spp. remain the most predominant nosocomial fungal infections. Owing to the increased use of antifungal agents, resistance of Candida spp. to antimycotics has emerged frequently, especially to fluconazole (FLC). To cope with this issue, new efforts have been dedicated to discovering novel antimycotics or new agents that can enhance the susceptibility of Candida spp. to existing antimycotics. The secondary metabolites of plants represent a large library of compounds that are important sources for new drugs or compounds suitable for further modification. Research on the anti-Candida activities of phytocompounds has been carried out in recent years and the results showed that a series of phytocompounds have anti-Candida properties, such as phenylpropanoids, flavonoids, terpenoids and alkaloids. Among these phytocompounds, some displayed potent antifungal activity, with minimum inhibitory concentrations (MICs) of ≤8 µg/mL, and several compounds were even more effective against drug-resistant Candida spp. than FLC or itraconazole (e.g. honokiol, magnolol and shikonin). Interestingly, quite a few phytocompounds not only displayed anti-Candida activity alone but also synergised with FLC against Candida spp., even leading to a reversal of FLC resistance. This review focuses on summarising the anti-Candida activities of phytocompounds as well as the interactions of phytocompounds with FLC. In addition, we briefly overview the synergistic mechanisms and present the structure of the antimycotic phytocompounds. Hopefully, this analysis will provide insight into antifungal agent discovery and new approaches against antifungal drug resistance.

Metabolic Changes of Caffeine in Tea Plant (Camellia sinensis (L.) O. Kuntze) as Defense Response to Colletotrichum fructicola

Tea plant (Camellia sinensis) is one of the most economically valuable crops in the world. Anthracnose can affect the growth of leaves and cause serious yield losses of tea. Tea plants are rich in secondary metabolites; however, their roles in resistance to anthracnose are unclear. Herein we compared the contents of total phenolics, catechins, and caffeine in two cultivars with different resistances to anthracnose during Colletotrichum fructicola infection. (-)-Epigallocatechin-3-gallate (EGCG), (+)-catechin (C), caffeine, and critical regulatory genes were induced in C. fructicola-resistant tissues. In vitro antifungal tests showed that caffeine more strongly inhibited mycelial growth than tea polyphenols and catechins. Both electron microscopy and bioactivity analysis results showed that caffeine can affect mycelial cell walls and plasma membranes. Through promoter sequences analysis, a number of stress response-related cis-acting elements were identified in S-adenosylmethionine synthetase and tea caffeine synthase. These results demonstrated that (-)-EGCG, (+)-C, and caffeine may be involved in the resistance of tea plants to anthracnose.

Review of flavonoids: A diverse group of natural compounds with anti-Candida albicans activity in vitro

Flavonoids are a subdivision of polyphenols, a versatile class of natural compounds that represent secondary metabolites from higher plants and are abundant in human diet. Various protective effects of flavonoids have been reported, including antimicrobial and antifungal activities. Due to the nature of oral candidiasis and the increased use of antifungal agents, several drug-resistant strains have emerged making it impractical to rely on one standard therapeutic regime. The aim of this review is to summarize the antifungal activity of some examples of the major subclasses of flavonoids in pure extract forms against C. albicans in vitro, as reported in literature over the past 10 years (2004-2015). In addition, this review outlines the potential mechanism of actions of flavonoids studied in vitro, which may contribute to a better understanding of flavonoids as multi-targets agents in the treatment and/or prevention of oral candidiasis in clinical settings.