Antifungal activity of amphotericin B, caspofungin and posaconazole on Candida albicans biofilms in intermediate and mature development phases

Anti-Candida activity and biocompatibility of silver nanoparticles associated with denture glaze: a new approach to the management of denture stomatitis

The association of silver nanoparticles (AgNps) to sealant agent Palaseal® can be a promising alternative for complete denture wearers who may develop denture stomatitis (DS). The study aimed to evaluate the anti-Candida and biocompatible potential of silver nanoparticles synthesized by three routes associated with denture glaze to prevent and/or treat oral candidiasis. Surface acrylic resin specimens were treated with different associations of glaze with AgNps (VER+AgUV, VER+AgTurk and VER+AgGm). As controls, specimens were treated with glaze+nystatin (VER+Nyst), glaze only (VER) or submerged in PBS (PBS). Afterwards, Candida albicans biofilm was developed for 24 h, 15 d and 30 d. Subsequently, the biofilm was quantified by CFU/mL, XTT assay and confocal laser scanning microscopy. Fibroblasts were submitted to conditioned medium with the same associations for 24, 48 and 72 h and LIVE/DEAD® viability test was carried out. Regardless of the period, there was a significant reduction (p < 0.01) of viable fungal cells load, as well as inhibition of fungal metabolic activity, in specimens treated with glaze+AgNps associations, compared to VER and PBS. The anti-Candida effects of the associations were similar to the VER+Nyst group, with emphasis on VER+AgGm, which showed the highest percentage values of non-viable fungal cells maintained over time. The associations did not prove toxicity to fibroblasts. The AgNps exerted antimicrobial activity against C. albicans biofilms and are biocompatible. The most effective results were achieved with the association of glaze+silver nanoparticles synthesized by the green chemistry method (AgGm), proving to be an innovative alternative in the management of DS.

Establishing Quantifiable Guidelines for Antimicrobial α/β-Peptide Design: A Partial Least-Squares Approach to Improve Antimicrobial Activity and Reduce Mammalian Cell Toxicity

Antimicrobial peptides (AMPs) are promising candidates to combat pathogens that are resistant to conventional antimicrobial drugs because they operate through mechanisms that involve membrane disruption. However, the use of AMPs in clinical settings has been limited, at least in part, by their susceptibility to proteolytic degradation and their lack of selectivity toward pathogenic microbes vs mammalian cells. We recently reported on the design of α- and β-peptide oligomers structurally templated upon the naturally occurring α-helical AMP aurein 1.2. These α/β-peptide oligomers are more proteolytically stable than aurein 1.2 and have several other attributes that render them attractive as alternatives to conventional AMPs. This study describes the influence of peptide physicochemical properties on the broad-spectrum activity of aurein 1.2-based α/β-peptide mimics against nine bacterial, fungal, and mammalian cell lines. We used a partial least-squares regression (PLSR)-supervised machine learning model to quantify and visualize relationships between experimentally determined physicochemical properties (e.g., hydrophobicity, charge, and helicity) and experimentally measured cell-type-specific activities of 21 peptides in a 149-member α/β-peptide library. Using this approach, we identified several peptides that were predicted to exhibit enhanced broad-spectrum selectivity, a measure that evaluates antimicrobial activity relative to mammalian cell toxicity compared to aurein 1.2. Experimental validation demonstrated high model predictive performance, and characterization of compounds with the highest broad-spectrum selectivity revealed peptide hydrophobicity, helicity, and helical rigidity to be strong predictors of broad-spectrum selectivity. The most selective peptide identified from the model prediction has more than a 13-fold improvement in broad-spectrum selectivity than that of aurein 1.2, demonstrating the ability of using PLSR models to identify quantitative structure-function relationships for nonstandard amino acid-containing peptides. Overall, this work establishes quantifiable guidelines for the rational design of helical antimicrobial α/β-peptides and identifies promising new α/β-peptides with significantly reduced mammalian toxicities and improved antifungal and antibacterial activities relative to aurein 1.2.

Silver nanoparticles in denture adhesive: An antimicrobial approach against Candida albicans

OBJECTIVE

To evaluate the antimicrobial potential of silver nanoparticles (Ag NPs) synthesized using three different routes (ultraviolet light, Turkevich, and green chemistry method using Glycine max extract) associated with COREGA® denture powder adhesive.

METHODS

Heat-cured acrylic resin specimens were treated with different Ag NPs associated with the adhesive (AD + Ag UV, AD + Ag Turk, and AD + Ag Gm groups). As controls, the specimens were treated with a combination of adhesive and nystatin (AD + Nyst group), only adhesive (AD group), or submerged on the surface of the specimens (PBS group). After the treatments, biofilms of C. albicans developed for 3, 6, and 12 h on the specimen surfaces. The biofilm was quantified using colony-forming units per milliliter, colorimetric assay, and confocal laser scanning microscopy.

RESULTS

Regardless of the period, we observed an inhibition of fungal load and a reduction in metabolic activity and biofilm mass in the resin specimens treated with the combinations AD/Ag NPs, compared to AD and PBS. The antimicrobial action of the AD + Turk and AD + Ag Gm groups was similar than that for the AD + Nyst group in all periods and viability tests, except for the biofilm mass (12 h).

CONCLUSIONS

The COREGA® adhesive with Ag NPs, mainly those synthesized using the Turkevich and Glycine max methods, showed excellent antimicrobial activity against C. albicans biofilms, maintained for up to 12 h.

CLINICAL SIGNIFICANCE

The association of Ag NPs to the adhesive can add preventive or therapeutic effects against denture stomatitis, to this prosthetic material.

Antifungal activity of designed α-helical antimicrobial peptides

Antimicrobial resistance (AMR) has become a major global health concern prompting the quest for new antibiotics with higher efficiency and less proneness to drug resistance. Antimicrobial peptides (AMPs) offer such properties and have therefore gained increasing attention as a new generation of antibiotics to overcome AMR. In an attempt to develop new highly selective and highly efficient antifungal peptides, a sequence (named At1) originating from the natural AMP Ponericin-W1 was used as a lead sequence for rational design of a series of short cationic antifungal peptides named At2-At12. The charge, hydrophobicity, and terminal amino acids of the peptides were modified in a systematic way to investigate the effect of such structural changes on the biological activity of the peptides. Among all the designed peptides, three peptides (coded as At3, At5 and At10) exhibited high antifungal activity without any significant hemolytic activity in human red blood cells. The higher selectivity of these peptides for fungal cells over human cells was further confirmed in cocultures of Candida albicans and human foreskin fibroblasts. These three peptides lacked any hydrophilic residues in their hydrophobic domain, contained lysine residues in their hydrophilic region and had an overall charge of 7+. They also had a higher helical content in microbial membrane mimicking DPPG SUVs than the rest of the peptides. The fungi did not develop any resistance to the designed antifungal peptides even after 25 generations indicating low AMR. At5 was also used in vivo for the treatment of wounds infected with Candida albicans in mice and showed superiority over fluconazole for treating infection and accelerating wound healing. There was an interplay between the hydrophobicity and positive charge density to determine the antifungal activity of the peptides. The results from this study suggest this class of antifungal peptides as promising candidates for antifungal drugs with high efficiency, high biocompatibility and low propensity for drug resistance.

Osteoarticular Mycoses

Osteoarticular mycoses are chronic debilitating infections that require extended courses of antifungal therapy and may warrant expert surgical intervention. As there has been no comprehensive review of these diseases, the International Consortium for Osteoarticular Mycoses prepared a definitive treatise for this important class of infections. Among the etiologies of osteoarticular mycoses are Candida spp., Aspergillus spp., Mucorales, dematiaceous fungi, non-Aspergillus hyaline molds, and endemic mycoses, including those caused by Histoplasma capsulatum, Blastomyces dermatitidis, and Coccidioides species. This review analyzes the history, epidemiology, pathogenesis, clinical manifestations, diagnostic approaches, inflammatory biomarkers, diagnostic imaging modalities, treatments, and outcomes of osteomyelitis and septic arthritis caused by these organisms. Candida osteomyelitis and Candida arthritis are associated with greater events of hematogenous dissemination than those of most other osteoarticular mycoses. Traumatic inoculation is more commonly associated with osteoarticular mycoses caused by Aspergillus and non-Aspergillus molds. Synovial fluid cultures are highly sensitive in the detection of Candida and Aspergillus arthritis. Relapsed infection, particularly in Candida arthritis, may develop in relation to an inadequate duration of therapy. Overall mortality reflects survival from disseminated infection and underlying host factors.

Antifungal Mechanisms of a Chinese Herbal Medicine, Cao Huang Gui Xiang, Against Candida Species

Cao Huang Gui Xiang (CHGX) formula, a Chinese herbal medicine, has been empirically used for the treatment of Candida infections. In the present study, we discovered that the CHGX showed potent antifungal activities against the major human fungal pathogen Candida albicans and other clinical Candida species. Besides, we indicated that CHGX had in vivo efficacy on treating C. albicans infection in mice without noticeable toxicity at the clinical therapeutic concentration. We then set out to investigate the antifungal mechanisms of CHGX against C. albicans. We found that CHGX played an important role in inhibiting biofilm formation and filament development, two critical virulence factors of C. albicans. We further demonstrated that CHGX disrupted cell membrane integrity, triggered the accumulation of reactive oxygen species (ROS) and consumption of adenosine triphosphate (ATP), followed by a rapid fungal cell death in C. albicans. Multiple pathways, including the conserved Ras1-cAMP pathway and mitochondrial protein Mcu1 are involved in CHGX-induced cell death. Our finding expands the understanding of antifungal mechanism of CHGX against C. albicans, and provides new insights in treating patients with Candida infections in clinical practice.

Super aggregated amphotericin B with a thermoreversible in situ gelling ophthalmic system for amoebic keratitis treatment

Acanthamoeba spp. are the causative agents of a sight-threatening infection of the cornea known as Acanthamoeba keratitis (AK). Amphotericin B - deoxycholate (AB) is used in the treatment of infectious keratitis, however, its topical administration has side effects as blepharitis, iritis, and painful instillation. In this context, the preheating of AB can decrease its toxicity by the formation of super aggregates (hAB). hAB associated with a thermoreversible in situ gelling ophthalmic system is a promising option due to the latter biocompatibility, low toxicity, and high residence time on the ocular surface. Our objective was to develop a topical ocular formulation of hAB for the treatment of AK. After heating at 70°C for 20 min, hAB was incorporated into a thermoreversible gelling system. The amebicidal activity of AB and hAB was evaluated against trophozoites and cysts of A. castellanii (ATCC 50492) and a regional clinical isolate (IC01). The results showed that the preheating of AB did not change the pharmacological action of the drug, with the amebicidal effect of AB and hAB under trophozoites and cysts of Acanthamoeba spp. The thermoreversible system remained stable, allowing the increase of drug retention time. For assessment of cytotoxicity, HUVEC (ATCC® CRL-1730) cells were challenged with AB and hAB for 48h. Cell viability was assessed, and hAB did not show cytotoxicity for HUVEC cells. As far as we know this was the first study that showed the preheated AB associated with a thermoreversible in situ gelling ophthalmic system as a promising system for topical ocular topical administration of hAB for AK therapy.

Secondary Metabolites from Food-Derived Yeasts Inhibit Virulence of Candida albicans

A sparse number of available antifungal drugs, therapeutic side effects, and drug resistance are major challenges in current antifungal therapy to treat Candida albicans-associated infections. Here, we describe two food-derived yeasts, Saccharomyces cerevisiae and Issatchenkia occidentalis, that inhibit virulence traits of C. albicans, including hyphal morphogenesis, biofilm formation, and adhesion to intestinal epithelial cells. These yeasts also protect the model host Caenorhabditis elegans from C. albicans infection. We demonstrate that the protective activity is primarily retained in the secretome of the beneficial yeasts, and the protection they provide as a physical barrier is negligible. S. cerevisiae aro8 aro9 mutant analysis demonstrate that phenylethanol and tryptophol are necessary for protection, and experiments with commercially procured compounds indicate that they are sufficient to inhibit C. albicans virulence. We propose food-derived yeasts as an alternative or combination therapy to conventional antifungal therapy for C. albicans infection. IMPORTANCE The gut microbiome, primarily established by food, is complex and contributes to the health of the host. Molecular mechanisms that regulate microbial interactions and host health remain unclear. Here, we show that the pathogen C. albicans interacts with food-derived beneficial yeasts in the gut of the microscopic worm, C. elegans, forming a simple microbiome. C. albicans can colonize the worm gut, compromising the worm's health, and exposure to the food-derived yeasts ameliorates this effect protecting the nematode host. We identify small molecules from food-derived yeasts that are necessary and sufficient to inhibit multiple virulence traits of C. albicans and protect the nematode host. The nematode gut faithfully recapitulates a mammalian intestine. This could be an effective alternative or combination therapy for C. albicans infection.

CDATA[Recent Advances in the Development of 1,2,3-Triazole-containing Derivatives as Potential Antifungal Agents and Inhibitors of Lanoster ol 14α-Demethylase

1,2,3-Triazole, a five-membered heterocyclic nucleus, is widely recognized as a key chromophore of great value in medicinal chemistry for delivering compounds possessing innumerable biological activities, including antimicrobial, antitubercular, antidiabetic, antiviral, antitumor, antioxidants, and anti-inflammatory activities. Mainly, in the past years, diverse conjugates carrying this biologically valuable core have been reported due to their attractive fungicidal potential and potent effects on various infective targets. Hence, hybridization of 1,2,3-triazole with other antimicrobial pharmacophores appears to be a judicious strategy to develop new effective anti-fungal candidates to combat the emergence of drug-sensitive and drug-resistant infectious diseases. Thus, the current review highlights the recent advances of this promising category of 1,2,3-triazole-containing hybrids incorporating diverse varieties of bioactive heterocycles such as conozole, coumarin, imidazole, benzimidazole, pyrazole, indole, oxindole, chromene, pyrane, quinazoline, chalcone, isoflavone, carbohydrates, and amides. It underlies their inhibition behavior against a wide array of infectious fungal species during 2015-2020.

[AmBisome, three challenges: Candida auris infection, central nervous system infection, and biofilm-associated infection]

The treatment of invasive fungal infections remains a challenge, both for the diagnosis and for the need of providing the appropriate antifungal therapy. Candida auris is a pathogenic yeast that is responsible for hospital outbreaks, especially in intensive care units; it is characterized by a high resistance to the antifungal agents and can become multidrug-resistant. At present, the recommended antifungal agents for the invasive infections with this pathogen are echinocandins, always after carrying out an antifungal susceptibility testing. In case of no clinical response or persistent candidemia, the addition of liposomal amphotericin B or isavuconazole may be considered. Both fungal infection of the central nervous system and that associated with biomedical devices remain rare entities affecting mainly immunocompromised patients. However, an increase in their incidence in recent years, along with high morbidity and mortality, has been shown. The treatment of these infections is conditioned by the limited knowledge of the pharmacokinetic properties of antifungals. A better understanding of the pharmacokinetic and pharmacodynamic parameters of the different antifungals is essential to determine the efficacy of the antifungal agents in the treatment of these infections.

Fibrin Biopolymer Incorporated with Antimicrobial Agents: A Proposal for Coating Denture Bases

The characteristics of the denture base surface, in combination with the oral environment, promote the colonization and development of Candida albicans biofilm, which is the main cause of denture stomatitis. This study evaluated the effectiveness of fibrin biopolymer with digluconate chlorhexidine or Punica granatum alcoholic extract to prevent C. albicans biofilm. Conventional heat polymerized and pre-polymerized poly(methyl methacrylate) (PMMA) circular specimens (10 × 2 mm) were fabricated (n = 504) and randomly divided into groups: no treatment (control—CT), fibrin biopolymer coating (FB), fibrin biopolymer with P. granatum (FBPg), or digluconate of chlorhexidine (FBCh) coating. The specimens were inoculated with C. albicans SC5314 (1 × 10⁷ cells/mL) and incubated for 24, 48, and 72 h. Crystal violet and colony-forming unit assays were used to quantify the total biofilm biomass and biofilm-living cells. A qualitative analysis was performed using confocal laser scanning microscopy. Data obtained are expressed as means and standard deviations and were statistically analyzed using a three-way analysis of variance (α = 0.05). The FBPg and FBCh groups inhibited the growth of C. albicans biofilm in both PMMA materials analyzed, with FBCh performing better in all periods evaluated (p < 0.0001). The colony forming unit (CFU) assay showed that the FB group favored the C. albicans biofilm growth at 24 h and 48 h (p < 0.0001), with no differences with CT group at 72 h (p = 0.790). All groups showed an enhancement in biofilm development up to 72 h (p < 0.0001), except the FBCh group (p = 0.100). No statistical differences were found between the PMMA base materials (p > 0.050), except in the FB group (p < 0.0001). Fibrin biopolymer, albeit a scaffold for the growth of C. albicans, when combined with chlorhexidine digluconate or P. granatum, demonstrated excellent performance as a drug delivery system, preventing and controlling the formation of denture biofilm.

Proposal for a microcosm biofilm model for the study of vulvovaginal candidiasis

This study proposes a microcosm biofilm (MiB) model for the study of vulvovaginal candidiasis (VVC). Different conditions that mimic the vaginal environment were tested for MiB formation. The best growth conditions were obtained with samples incubated in vaginal fluid simulator medium pH 4.5 at 35 °C under a microaerophilic atmosphere. MiBs were evaluated for growth kinetics, fluconazole susceptibility and morphology. Samples containing high numbers of bacteria were analyzed for metagenomics. At 48 h, MiBs presented a higher cell density (CFU ml^-1), a higher biomass and tolerance to fluconazole than their corresponding monospecies biofilms. Morphological analysis of MiBs revealed blastoconidia preferentially adhered to epithelial cells. Abundant Lactobacillus spp. were detected in two clinical samples; their MiBs showed a lower biomass and a higher fluconazole susceptibility. The proposed model proved to be a useful tool for the study of the complex microbial relationship in the vaginal environment, and may help to find new strategies for VVC control.

Inhibitory effect of novel Eugenol Tosylate Congeners on pathogenicity of Candida albicans

BACKGROUND

The global prevalence of fungal diseases is increasing rapidly, which affects more than a billion people every year with significant mortality rate. On the other hand, the development of new drugs to treat these fungal infections is slow, while the current antifungal therapy is insufficient and associated with adverse side effects and emerging multidrug resistance. Therefore, development of novel antifungal drugs with least or no toxicity and multi-target mechanisms of action is an immediate priority. Natural products have long been known to possess antimicrobial activities and are source of new drugs. Currently, modifying natural products to synthesize derivatives/analogues are of great scientific focus for discovering novel drugs with improved potency and safety. Modifications in eugenol to synthesize eugenol derivatives with enhanced antifungal activity have already been reported.

METHODS

In this study, three most active novel eugenol tosylate congeners (ETC-5, ETC-6 and ETC-7) were selected from our previous study to investigate their effect on major virulence factors of Candida albicans which include adherence, morphogenesis, hydrolytic enzymes secretion, biofilm formation and on expression of genes related to these virulence factors. Adherence and biofilm formation were studied by alamarBlue dye and XTT reduction assays respectively, hydrolytic enzyme secretion was evaluated by plate assays. Further, morphological transition was monitored microscopically and RT-qPCR was used to assess the gene expression levels.

RESULTS

ETCs significantly inhibited adherence in C. albicans with an inhibition range of 16-66%, and completely inhibited the morphogenesis at MIC values. Inhibition of proteinase and phospholipase activity was in the range of 2-48% and 8-34% respectively. Test compounds also significantly inhibit biofilm formation in C. albicans in the range of 7-77%. Furthermore, RT-qPCR results indicated a significant down regulation in expression levels of genes (ALS1, ALS2, ALS3, ALS9, CPH1, HWP1, SAP1, SAP2, SAP3 and PLB1) in C. albicans cells after treated with ETCs.

CONCLUSION

The results indicated that these novel ETCs target major virulence factors of C. albicans and avert this commensal microbe to turn into pathogenic. However, further in-depth studies may facilitate the mechanisms involved by ETCs in targeting these virulence factors.

Candida Biofilms: An Update on Developmental Mechanisms and Therapeutic Challenges

Fungi of the genus Candida are important etiological agents of superficial and life-threatening infections in individuals with a compromised immune system. One of the main characteristics of Candida is its ability to form highly drug tolerance biofilms in the human host. Biofilms are a dynamic community of multiple cell types whose formation over time is orchestrated by a network of transcription regulators. In this brief review, we provide an update of the processes involved in biofilm formation by Candida spp. (formation, treatment, and control), as well as the transcriptional circuitry that regulates its development and interactions with other microorganisms. Candida albicans is known to build mixed species biofilms with other Candida species and with various other bacterial species in different host niches. Taken together, these properties play a key role in Candida pathogenesis. In addition, this review gathers recent studies with new insights and perspectives for the treatment and control of Candida biofilms.

A Paradigm Shift in the Development of Anti-Candida Drugs

BACKGROUND

The considerable increase in the incidence of Candida infection in recent times has prompted the use of numerous antifungal agents, which has resulted in the development of resistance towards various antifungal agents. With rising Candida infections, the need for design and development of novel antifungal agents is in great demand. However, new therapeutic approaches are very essential in preventing the mortality rate and improving the patient outcome in those suffering from Candida infections.

OBJECTIVE

The present review objective is to describe the burden, types of Candidiasis, mechanism of action of antifungal agents and its resistance and the current novel approaches used to combat candidiasis.

METHODS

We have collected and analyzed 135 different peer-reviewed literature studies pertinent to candidiasis. In this review, we have compiled the major findings from these studies.

RESULTS AND CONCLUSION

The review describes the concerns related to candidiasis, its current treatment strategy, resistance mechanisms and imminent ways to tackle the problem. The review explored that natural plant extracts and essential oils could act as sources of newer therapeutic agents, however, the focus was on novel strategies, such as combinational therapy, new antibodies, utilization of photodynamic therapy and adaptive transfer primed immune cells with emphasis on the development of effective vaccination.

The Synergism of the Small Molecule ENOblock and Fluconazole Against Fluconazole-Resistant Candida albicans

Candida albicans is the most common opportunistic fungal pathogen which can cause life-threatening bloodstream infections known as candidaemia. It is very important to discover new drugs and targets for the treatment of candidaemia. In this study, we first investigated the combination antifungal effects of the small molecule ENOblock and fluconazole (FLC) against FLC-resistant C. albicans. A checkerboard microdilution assay showed that ENOblock has a significant synergistic effect in combination with FLC against FLC-resistant C. albicans. The time-kill curve further confirmed the synergism of this compound with FLC against FLC-resistant C. albicans. Moreover, we demonstrated the significant inhibitory effects of ENOblock alone and in combination with FLC against C. albicans hypha and biofilm formation. Furthermore, the XTT assay showed that ENOblock has relatively low toxicity to human umbilical vein endothelial cells. The in vivo antifungal efficacy of ENOblock was further assessed in a murine model of systemic C. albicans infection. Although ENOblock alone was not sufficient to treat C. albicans infection, the combination of FLC and ENOblock showed significant in vivo activity against FLC-resistant C. albicans. Finally, using surface plasmon resonance analysis as well as an inhibition assay, we determined that ENOblock directly interacted with CaEno1 and significantly inhibited the transglutaminase activity of this enzyme, which is involved in the growth and morphogenesis of C. albicans. In summary, these results demonstrate the synergistic effects of FLC and ENOblock against FLC-resistant C. albicans, and indicate that inhibition of the transglutaminase activity of CaEno1 by ENOblock might confer an advantage for the synergism of FLC and ENOblock, suggesting the potential of ENOblock as a new antifungal candidate.

Inhibition of Biofilm Formation by Candida albicans and Polymicrobial Microorganisms by Nepodin via Hyphal-Growth Suppression

Candida albicans is an opportunistic pathogenic yeast and is responsible for candidiasis. It readily colonizes host tissues and implant devices, and forms biofilms, which play an important role in pathogenesis and drug resistance. In this study, the antibiofilm, antihyphal, and antivirulence activities of nepodin, isolated from Rumex japonicus roots, were investigated against a fluconazole-resistant C. albicans strain and against polymicrobial-microorganism-biofilm formation. Nepodin effectively inhibited C. albicans biofilm formation without affecting its planktonic cell growth. Also, Rumex-root extract and nepodin both inhibited hyphal growth and cell aggregation of C. albicans. Interestingly, nepodin also showed antibiofilm activities against Candida glabrata, Candida parapsilosis, Staphylococcus aureus, and Acinetobacter baumannii strains and against dual biofilms of C. albicans and S. aureus or A. baumannii but not against Pseudomonas aeruginosa. Transcriptomic analysis performed by RNA-seq and qRT-PCR showed nepodin repressed the expression of several hypha- and biofilm-related genes (ECE1, HGT10, HWP1, and UME6) and increased the expression of several transport genes (CDR4, CDR11, and TPO2), which supported phenotypic changes. Moreover, nepodin reduced C. albicans virulence in a nematode-infection model and exhibited minimal cytotoxicity against the nematode and an animal cell line. These results demonstrate that nepodin and Rumex-root extract might be useful for controlling C. albicans infections and multispecies biofilms.

Effect of Shikonin Against Candida albicans Biofilms

Candidiasis is often associated with the formation of biofilms. Candida albicans biofilms are inherently resistant to many clinical antifungal agents and have increasingly been found to be the sources of C. albicans infections. Novel antifungal agents against C. albicans biofilms are urgently needed. The aim of this study was to investigate the effect of shikonin (SK) against C. albicans biofilms and to clarify the underlying mechanisms. XTT reduction assay showed that SK could not only inhibit the formation of biofilms but also destroy the maintenance of mature biofilms. In a mouse vulvovaginal candidiasis (VVC) model, the fungal burden was remarkably reduced upon SK treatment. Further study showed that SK could inhibit hyphae formation and reduce cellular surface hydrophobicity (CSH). Real-time reverse transcription-PCR analysis revealed that several hypha- and adhesion-specific genes were differentially expressed in SK-treated biofilm, including the downregulation of ECE1, HWP1, EFG1, CPH1, RAS1, ALS1, ALS3, CSH1 and upregulation of TUP1, NRG1, BCR1. Moreover, SK induced the production of farnesol, a quorum sensing molecule, and exogenous addition of farnesol enhanced the antibiofilm activity of SK. Taken together, these results indicated that SK could be a favorable antifungal agent in the clinical management of C. albicans biofilms.

Efficacy of 7-benzyloxyindole and other halogenated indoles to inhibit Candida albicans biofilm and hyphal formation

Certain pathogenic bacteria and yeast form biofilms on biotic and abiotic surfaces including medical devices and implants. Hence, the development of antibiofilm coating materials becomes relevant. The virulence of those colonizing pathogens can be reduced by inhibiting biofilm formation rather than killing pathogens using excessive amounts of antimicrobials, which is touted as one of the main reasons for the development of drug resistance. Candida albicans is an opportunistic fungal pathogen, and the transition of yeast cells to hyphal cells is believed to be a crucial virulence factor. Previous studies have shown that indole and its derivatives possess antivirulence properties against various bacterial pathogens. In this study, we used various indole derivatives to investigate biofilm-inhibiting activity against C. albicans. Our study revealed that 7-benzyloxyindole, 4-fluoroindole and 5-iodoindole effectively inhibited biofilm formation compared to the antifungal agent fluconazole. Particularly, 7-benzyloxyindole at 0.02 mM (4.5 μg ml-1 ) significantly reduced C. albicans biofilm formation, but had no effect on planktonic cells, and this finding was confirmed by a 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) assay and three-dimensional confocal laser scanning microscopy. Scanning electron microscopy analyses revealed that 7-benzyloxyindole effectively inhibited hyphal formation, which explains biofilm inhibition. Transcriptomic analysis showed that 7-benzyloxyindole downregulated the expressions of several hypha/biofilm-related genes (ALS3, ECE1, HWP1 and RBT1). A C. albicans-infected Caenorhabditis elegans model system was used to confirm the antivirulence efficacy of 7-benzyloxyindole.

(1-aryloxy-2-hydroxypropyl)-phenylpiperazine derivatives suppress Candida albicans virulence by interfering with morphological transition

Clinical treatment of Candida albicans infections has become more difficult due to the limited development of antifungal agents and the rapid emergence of drug resistance. In this study, we demonstrate the synthesis of a series of piperazine derivatives and the evaluation of their inhibitory activity against C. albicans virulence. Thirty-four (1-aryloxy-2-hydroxypropyl)-phenylpiperazine derivatives, including 25 new compounds, were synthesized and assessed for their efficacy against the physiology and pathogenesis of C. albicans. Several compounds strongly inhibited the morphological transition and virulence of C. albicans cells, although they did not influence the growth rate of the fungal pathogen. A leading novel compound, (1-(4-ethoxyphenyl)-4-(1-biphenylol-2-hydroxypropyl)-piperazine), significantly attenuated C. albicans virulence by interfering with the process of hyphal development, but it showed no cytotoxicity against human cells at a micromolar level. These findings suggest that (1-aryloxy-2-hydroxypropyl)-phenylpiperazine derivatives could potentially be developed as novel therapeutic agents for the clinical treatment of C. albicans infections by interfering with morphological transition and virulence.

Antibiofilm and Antivirulence Activities of 6-Gingerol and 6-Shogaol Against Candida albicans Due to Hyphal Inhibition

Candida albicans is an opportunistic pathogen and responsible for candidiasis. C. albicans readily forms biofilms on various biotic and abiotic surfaces, and these biofilms can cause local and systemic infections. C. albicans biofilms are more resistant than its free yeast to antifungal agents and less affected by host immune responses. Transition of yeast cells to hyphal cells is required for biofilm formation and is believed to be a crucial virulence factor. In this study, six components of ginger were investigated for antibiofilm and antivirulence activities against a fluconazole-resistant C. albicans strain. It was found 6-gingerol, 8-gingerol, and 6-shogaol effectively inhibited biofilm formation. In particular, 6-shogaol at 10 μg/ml significantly reduced C. albicans biofilm formation but had no effect on planktonic cell growth. Also, 6-gingerol and 6-shogaol inhibited hyphal growth in embedded colonies and free-living planktonic cells, and prevented cell aggregation. Furthermore, 6-gingerol and 6-shogaol reduced C. albicans virulence in a nematode infection model without causing toxicity at the tested concentrations. Transcriptomic analysis using RNA-seq and qRT-PCR showed 6-gingerol and 6-shogaol induced several transporters (CDR1, CDR2, and RTA3), but repressed the expressions of several hypha/biofilm related genes (ECE1 and HWP1), which supported observed phenotypic changes. These results highlight the antibiofilm and antivirulence activities of the ginger components, 6-gingerol and 6-shogaol, against a drug resistant C. albicans strain.

In vitro activities of antifungals alone and in combination with tigecycline against Candida albicans biofilms

Background

Candida may form biofilms, which are thought to underlie the most recalcitrant infections.

Methods

In this study, activities of antifungal agents alone and in combination with tigecycline against planktonic cells and mature and developing biofilms of Candida albicans isolates were evaluated.

Results

Amphotericin B and echinocandins were found to be the most effective agents against mature biofilms, whereas the least effective agent was fluconazole. Furthermore, the most effective anti-fungal monotherapies against biofilm formation were amphotericin B and anidulafungin, and the least effective monotherapy was itraconazole. The combination of tigecycline and amphotericin B yielded synergistic effects, whereas combinations containing itraconazole yielded antagonist effects against planktonic cells. The combination of tigecycline and caspofungin exhibited maximum efficacy against mature biofilms, whereas combinations containing itraconazole exhibited minimal effects. Combinations of tigecycline with amphotericin B or anidulafungin were highly effective against C. albicans biofilm formation.

Discussion

In summary, tigecycline was highly active against C. albicans particularly when combined with amphotericin B and echinocandins.

What Could Be the Role of Antifungal Lock-Solutions? From Bench to Bedside

Candidemia related to the presence of a biofilm are often reported in patients with vascular catheters. Once they are mature, biofilms are persistent infectious reservoirs, and the yeasts dispersed from biofilms can cause infections. Sessile yeasts typically display increased levels of resistance to most antimicrobial agents and systemic treatments usually fail to eradicate previously formed fungal biofilms. In a curative strategy, antifungal lock therapy may help to sterilize catheters, with very high concentrations of antifungal agents, which are not compatible with systemic use. This strategy has been studied by several authors in in vitro and in vivo studies, and more rarely, in clinical settings for adult and paediatric patients. Our study aims to assess the efficacy of the antifungal solutions used for lock therapy and demonstrated by the different teams.

Biofilm-forming capacity of blood-borne Candida albicans strains and effects of antifungal agents

Infections related to Candida albicans biofilms and subsequent antifungal resistance have become more common with the increased use of indwelling medical devices. Regimens for preventing fungal biofilm formation are needed, particularly in high-risk patients. In this study, we investigated the biofilm formation rate of multiple strains of Candida albicans (n=162 clinical isolates), their antifungal susceptibility patterns, and the efficacy of certain antifungals for preventing biofilm formation. Biofilm formation was graded using a modified Christensen's 96-well plate method. We further analyzed 30 randomly chosen intense biofilm-forming isolates using the XTT method. Minimum biofilm inhibition concentrations (MBIC) of caspofungin, micafungin, anidulafungin, fluconazole, voriconazole, posaconazole, itraconazole, and amphotericin B were determined using the modified Calgary biofilm method. In addition, the inhibitory effects of antifungal agents on biofilm formation were investigated. Our study showed weak, moderate, and extensive biofilm formation in 29% (n=47), 38% (n=61), and 23% (n=37) of the isolates, respectively. We found that echinocandins had the lowest MBIC values and that itraconazole inhibited biofilm formation in more isolates (26/32; 81.3%) than other tested agents. In conclusion, echinocandins were most effective against formed biofilms, while itraconazole was most effective for preventing biofilm formation. Standardized methods are needed for biofilm antifungal sensitivity tests when determining the treatment and prophylaxis of C. albicans infections.

Anti-biofilm activity of a sophorolipid-amphotericin B niosomal formulation against Candida albicans

Sophorolipids (SLs) have gained interest in the pharmaceutical industries due to their anti-microbial, anti-adhesive and anti-biofilm properties. In the present study, the production of SL was increased by using low-cost media components. The potential of a SL-based niosomal formulation of amphotericin B (AmB) was determined against biofilm of the opportunistic fungal pathogen Candida albicans. In-house prepared SL-AmB niosomes were characterized by different microscopic techniques. The mean entrapment efficiency of AmB within SL-AmB niosome was 63.20% ± 3.86. The cytotoxicity of SL-AmB on mature C. albicans biofilm was compared with an expensive, marketed drug, viz. phosome (a liposomal formulation of AmB). Fewer hyphae were observed in C. albicans biofilm treated with SL-AmB niosome whereas more budding cells were found in phosome treated biofilm. The present study has established the affordable production of SL and the suitability of this approach for delivery of poorly soluble drugs such as AmB against candidiasis infections.

Activity of Sanguinarine against Candida albicans Biofilms

Candida albicans biofilms show resistance to many clinical antifungal agents and play a considerable contributing role in the process of C. albicans infections. New antifungal agents against C. albicans biofilms are sorely needed. The aim of this study was to evaluate sanguinarine (SAN) for its activity against Candida albicans biofilms and explore the underlying mechanism. The MIC₅₀ of SAN was 3.2 μg/ml, while ≥0.8 μg/ml of SAN could suppress C. albicans biofilms. Further study revealed that ≥0.8 μg/ml of SAN could decrease cellular surface hydrophobicity (CSH) and inhibited hypha formation. Real-time reverse transcription-PCR (RT-PCR) results indicated that the exposure of C. albicans to SAN suppressed the expression of some adhesion- and hypha-specific/essential genes related to the cyclic AMP (cAMP) pathway, including ALS3, HWP1, ECE1, HGC1, and CYR1 Consistently, the endogenous cAMP level of C. albicans was downregulated after SAN treatment, and the addition of cAMP rescued the SAN-induced filamentation defect. In addition, SAN showed relatively low toxicity to human umbilical vein endothelial cells, the 50% inhibitory concentration (IC₅₀) being 7.8 μg/ml. Collectively, the results show that SAN exhibits strong activity against C. albicans biofilms, and the activity was associated with its inhibitory effect on adhesion and hypha formation due to cAMP pathway suppression.

The Structure-Activity Relationship of Pterostilbene Against Candida albicans Biofilms

Candida albicans biofilms contribute to invasive infections and dramatic drug resistance, and anti-biofilm agents are urgently needed in the clinic. Pterostilbene (PTE) is a natural plant product with potentials to be developed as an anti-biofilm agent. In this study, we evaluated the structure-activity relationship (SAR) of PTE analogues against C. albicans biofilms. XTT (Sodium 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide inner salt) reduction assay was used to evaluate the activity of the analogues against C. albicans biofilms. Knowing that hyphal formation is essential for C. albicans biofilms, anti-hyphal assay was further carried out. By comparing a series of compounds tested in this study, we found that compounds with para-hydroxy (–OH) in partition A exhibited better activity than those with other substituents in the para position, and the double bond in partition B and meta-dimethoxy (–OCH₃) in partition C both contributed to the best activity. Consistent results were obtained by anti-hyphal assay. Collectively, para-hydroxy (–OH), double bond and meta-dimethoxy (–OCH₃) are all needed for the best activity of PTE against C. albicans biofilms.

Future therapies targeted towards eliminating Candida biofilms and associated infections

INTRODUCTION

Candida species are common human commensals and cause either superficial or invasive opportunistic infections. The biofilm form of candida as opposed to its suspended, planktonic form, is predominantly associated with these infections. Alternative or adjunctive therapies are urgently needed to manage Candida infections as the currently available short arsenal of antifungal drugs has been compromised due to their systemic toxicity, cross-reactivity with other drugs, and above all, by the emergence of drug-resistant Candida species due to irrational drug use. Areas covered: Combination anti-Candida therapies, antifungal lock therapy, denture cleansers, and mouth rinses have all been proposed as alternatives for disrupting candidal biofilms on different substrates. Other suggested approaches for the management of candidiasis include the use of natural compounds, such as probiotics, plants extracts and oils, antifungal quorum sensing molecules, anti-Candida antibodies and vaccines, cytokine therapy, transfer of primed immune cells, photodynamic therapy, and nanoparticles. Expert commentary: The sparsity of currently available antifungals and the plethora of proposed anti-candidal therapies is a distinct indication of the urgent necessity to develop efficacious therapies for candidal infections. Alternative drug delivery approaches, such as probiotics, reviewed here is likely to be a reality in clinical settings in the not too distant future.

Antifungal peptides: To be or not to be membrane active

Most antifungal peptides (AFPs), if not all, have membrane activity, while some also have alternative targets. Fungal membranes share many characteristics with mammalian membranes with only a few differences, such as differences in sphingolipids, phosphatidylinositol (PI) content and the main sterol is ergosterol. Fungal membranes are also more negative and a better target for cationic AFPs. Targeting just the fungal membrane lipids such as phosphatidylinositol and/or ergosterol by AFPs often translates into mammalian cell toxicity. Conversely, a specific AFP target in the fungal pathogen, such as glucosylceramide, mannosyldiinositol phosphorylceramide or a fungal protein target translates into high pathogen selectivity. However, a lower target concentration, absence or change in the specific fungal target can naturally lead to resistance, although such resistance in turn could result in reduced pathogen virulence. The question is then to be or not to be membrane active - what is the best choice for a successful AFP? In this review we deliberate on this question by focusing on the recent advances in our knowledge on how natural AFPs target fungi.

The clinical importance of fungal biofilms

Fungal biofilms have become an increasingly important clinical problem. The widespread use of antibiotics, frequent use of indwelling medical devices, and a trend toward increased patient immunosuppression have resulted in a creation of opportunity for clinically important yeasts and molds to form biofilms. This review will discuss the diversity and importance of fungal biofilms in the context of clinical medicine, provide novel insights into the clinical management of fungal biofilm infection, present evidence why these structures are recalcitrant to antifungal therapy, and discuss how our knowledge and understanding may lead to novel therapeutic intervention.

Antifungals: Mechanism of Action and Drug Resistance

There are currently few antifungals in use which show efficacy against fungal diseases. These antifungals mostly target specific components of fungal plasma membrane or its biosynthetic pathways. However, more recent class of antifungals in use is echinocandins which target the fungal cell wall components. The availability of mostly fungistatic antifungals in clinical use, often led to the development of tolerance to these very drugs by the pathogenic fungal species. Thus, the development of clinical multidrug resistance (MDR) leads to higher tolerance to drugs and its emergence is helped by multiple mechanisms. MDR is indeed a multifactorial phenomenon wherein a resistant organism possesses several mechanisms which contribute to display reduced susceptibility to not only single drug in use but also show collateral resistance to several drugs. Considering the limited availability of antifungals in use and the emergence of MDR in fungal infections, there is a continuous need for the development of novel broad spectrum antifungal drugs with better efficacy. Here, we briefly present an overview of the current understanding of the antifungal drugs in use, their mechanism of action and the emerging possible novel antifungal drugs with great promise.

Antifungal activity of cathelicidin peptides against planktonic and biofilm cultures of Candida species isolated from vaginal infections

Vulvovaginal candidiasis (VVC) is a frequent gynecological condition caused by Candida albicans and a few non-albicans Candida spp. It has a significant impact on the quality of life of the affected women also due to a considerable incidence of recurrent infections that are difficult to treat. The formation of fungal biofilm may contribute to the problematic management of recurrent VVC due to the intrinsic resistance of sessile cells to the currently available antifungals. Thus, alternative approaches for the prevention and control of biofilm-related infections are urgently needed. In this regard, the cationic antimicrobial peptides (AMPs) of the innate immunity are potential candidates for the development of novel antimicrobials as many of them display activity against biofilm formed by various microbial species. In the present study, we investigated the in vitro antifungal activities of the cathelicidin peptides LL-37 and BMAP-28 against pathogenic Candida spp. also including C. albicans, isolated from vaginal infections, and against C. albicans SC5314 as a reference strain. The antimicrobial activity was evaluated against planktonic and biofilm-grown Candida cells by using microdilution susceptibility and XTT [2,3-bis(2-methoxy-4-nitro-5-sulfo-phenyl)-2H-tetrazolium-5-carboxanilide] reduction assays and, in the case of established biofilms, also by CFU enumeration and fluorescence microscopy. BMAP-28 was effective against planktonically grown yeasts in standard medium (MIC range, 2-32μM), and against isolates of C. albicans and Candida krusei in synthetic vaginal simulated fluid (MIC range 8-32μM, depending on the pH of the medium). Established 48-h old biofilms formed by C. albicans SC5314 and C. albicans and C. krusei isolates were 70-90% inhibited within 24h incubation with 16μM BMAP-28. As shown by propidium dye uptake and CFU enumeration, BMAP-28 at 32μM killed sessile C. albicans SC5314 by membrane permeabilization with a faster killing kinetics compared to 32μM miconazole (80-85% reduced biofilm viability in 90min vs 48h). In addition, BMAP-28 at 16μM prevented Candida biofilm formation on polystyrene and medical grade silicone surfaces by causing a >90% reduction in the viability of planktonic cells in 30min. LL-37 was overall less effective than BMAP-28 against planktonic Candida spp. (MIC range 4-≥64μM), and was ineffective against established Candida biofilms. However, LL-37 at 64μM prevented Candida biofilm development by inhibiting cell adhesion to polystyrene and silicone surfaces. Finally, Candida adhesion was strongly inhibited when silicone was pre-coated with a layer of BMAP-28 or LL-37, encouraging further studies for the development of peptide-based antimicrobial coatings.

Synthesis, morphology and antifungal activity of nano-particulated amphotericin-B, ketoconazole and thymoquinone against Candida albicans yeasts and Candida biofilm

In the current study, nano-particulated drugs-Amphotericin-B, Ketoconazole and Thymoquinone (an active ingredient of Nigella sativa)-were prepared using the ball milling technique, and their particle sizes were examined by transmission electron microscopy (TEM) and using a particle size analyzer. The grain sizes of the prepared compounds were found in between 5 to 20 nm, and exhibited quasi-spherical morphology. The antifungal activity of each nano-particulated drug was investigated in vitro against Candida albicans yeasts and Candida biofilm, and compared with their micro-structured conventional forms. Nano-sized drugs were found to be two to four times more effective in disinfecting both the Candida yeasts and Candida biofilm. The study is a first of its kind as nano-forms of drugs have not been studied against Candida and Candida biofilm before. Further investigations are required for the determination of the clinical significance of the nano-formulation of antifungal substances.

Novel strategies to fight Candida species infection

In recent years, there has been a significant increase in the incidence of human fungal infections. The increase in cases of infection caused by Candida species, and the consequent excessive use of antimicrobials, has favored the emergence of resistance to conventional antifungal agents over the past decades. Consequently, Candida infections morbidity and mortality are also increasing. Therefore, new approaches are needed to improve the outcome of patients suffering from Candida infections, because it seems unlikely that the established standard treatments will drastically lower the morbidity of mucocutaneous Candida infections and the high mortality associated with invasive candidiasis. This review aims to present the last advances in the traditional antifungal therapy, and present an overview of novel strategies that are being explored for the treatment of Candida infections, with a special focus on combined antifungal agents, antifungal therapies with alternative compounds (plant extracts and essential oils), adjuvant immunotherapy, photodynamic therapy and laser therapy.

Synergistic activity of the tyrocidines, antimicrobial cyclodecapeptides from Bacillus aneurinolyticus, with amphotericin B and caspofungin against Candida albicans biofilms

Tyrocidines are cationic cyclodecapeptides from Bacillus aneurinolyticus that are characterized by potent antibacterial and antimalarial activities. In this study, we show that various tyrocidines have significant activity against planktonic Candida albicans in the low-micromolar range. These tyrocidines also prevented C. albicans biofilm formation in vitro. Studies with the membrane-impermeable dye propidium iodide showed that the tyrocidines disrupt the membrane integrity of mature C. albicans biofilm cells. This membrane activity correlated with the permeabilization and rapid lysis of model fungal membranes containing phosphatidylcholine and ergosterol (70:30 ratio) induced by the tyrocidines. The tyrocidines exhibited pronounced synergistic biofilm-eradicating activity in combination with two key antifungal drugs, amphotericin B and caspofungin. Using a Caenorhabditis elegans infection model, we found that tyrocidine A potentiated the activity of caspofungin. Therefore, tyrocidines are promising candidates for further research as antifungal drugs and as agents for combinatorial treatment.

Mechanisms of Candida biofilm drug resistance

Candida commonly adheres to implanted medical devices, growing as a resilient biofilm capable of withstanding extraordinarily high antifungal concentrations. As currently available antifungals have minimal activity against biofilms, new drugs to treat these recalcitrant infections are urgently needed. Recent investigations have begun to shed light on the mechanisms behind the profound resistance associated with the biofilm mode of growth. This resistance appears to be multifactorial, involving both mechanisms similar to conventional, planktonic antifungal resistance, such as increased efflux pump activity, as well as mechanisms specific to the biofilm lifestyle. A unique biofilm property is the production of an extracellular matrix. Two components of this material, β-glucan and extracellular DNA, promote biofilm resistance to multiple antifungals. Biofilm formation also engages several stress response pathways that impair the activity of azole drugs. Resistance within a biofilm is often heterogeneous, with the development of a subpopulation of resistant persister cells. In this article we review the molecular mechanisms underlying Candida biofilm antifungal resistance and their relative contributions during various growth phases.

Reactive oxygen species-inducing antifungal agents and their activity against fungal biofilms

Invasive fungal infections are associated with very high mortality rates ranging from 20–90% for opportunistic fungal pathogens such as Candida albicans, Cryptococcus neoformans and Aspergillus fumigatus. Fungal resistance to antimycotic treatment can be genotypic (due to resistant strains) as well as phenotypic (due to more resistant fungal lifestyles, such as biofilms). With regard to the latter, biofilms are considered to be critical in the development of invasive fungal infections. However, there are only very few antimycotics, such as miconazole (azoles), echinocandins and liposomal formulations of amphotericin B (polyenes), which are also effective against fungal biofilms. Interestingly, these antimycotics all induce reactive oxygen species (ROS) in fungal (biofilm) cells. This review provides an overview of the different classes of antimycotics and novel antifungal compounds that induce ROS in fungal planktonic and biofilm cells. Moreover, different strategies to further enhance the antibiofilm activity of such ROS-inducing antimycotics will be discussed.

The effect of antifungal combination on transcripts of a subset of drug-resistance genes in clinical isolates of Candida species induced biofilms

Biofilm formation is often associated with increased Candida resistance toward antifungal agents. Therefore, the current study aimed to assess the incidence of biofilm formation among Candida isolates and to investigate the effect of high doses of fluconazole {FLC}, voriconazole {VOC} and amphotericin B {AMB}, singly and in combination on mature biofilms. Moreover, it aimed to assess the expression of selected genes (CDR1, KRE1 and SKN1) responsible for Candida biofilm resistance. The study included 49 patients; samples were collected from the King Khalid Hospital, Riyadh, Saudi Arabia. Isolates were prepared for biofilm formation and quantification using 0.4% (w/v) crystal violet. Minimum Inhibitory concentration (MIC) and fractional inhibitory concentration (FIC) were conducted by the broth microdilution method. Biofilm eradication was evaluated using counting, XTT stain intensity and observed under the inverted microscope. Selected genes were evaluated in Candida biofilms under the effect of antifungal exposure using QPCR. The major isolates were Candida albicans (65.3%) followed by Candida tropicalis and Candida glabrata. 77.6% of the strains were biofilm formers. AMB showed susceptibility in 87.8% of isolates, followed by VOC (77.6%) and FLC (67.3%). MIC50 and MIC90 were (0.03, 0.125), (0.5, 8), (2, >128) μg/ml for AMB, VOC and FLC, respectively. 34.7% and 18.4% of the isolates were antagonistic to AMB/FLC and AMB/VOC, respectively. Mature biofilms of ten selected isolates were found resistant to FLC (1000 μg/ml). VOR and AMB concentration required to inhibit biofilm formation was 16-250 fold higher than the MIC for planktonic cells. Isolates showed significant reduction with antifungal combination when compared with the untreated controls (p value ⩽ 0.01), or using fluconazole alone (p value ⩽ 0.05). High doses of the antifungals were employed to assess the effect on the persisters' selected gene expression. Marked over expression of SKN1 and to a lesser extent KRE1 was noticed among the mature biofilms treated with AMB alone or in combination after 1 h of exposure, and SKN1 expression was even more sharply induced after 24 h. No statistically significant over expression of CDR1 was observed in biofilms after exposure to high doses of FLC, VOC or any of the combinations used.

Characterization of biofilm formation and the role of BCR1 in clinical isolates of Candida parapsilosis

In Candida parapsilosis, biofilm formation is considered to be a major virulence factor. Previously, we determined the ability of 33 clinical isolates causing bloodstream infection to form biofilms and identified three distinct groups of biofilm-forming strains (negative, low, and high). Here, we establish two different biofilm structures among strains forming large amounts of biofilm in which strains with complex spider-like structures formed robust biofilms on different surface materials with increased resistance to fluconazole. Surprisingly, the transcription factor Bcr1, required for biofilm formation in Candida albicans and C. parapsilosis, has an essential role only in strains with low capacity for biofilm formation. Although BCR1 leads to the formation of more and longer pseudohyphae, it was not required for initial adhesion and formation of mature biofilms in strains with a high level of biofilm formation. Furthermore, an additional phenotype affected by BCR1 was the switch in colony morphology from rough to crepe, but only in strains forming high levels of biofilm. All bcr1Δ/Δ mutants showed increased proteolytic activity and increased susceptibility to the antimicrobial peptides protamine and RP-1 compared to corresponding wild-type and complemented strains. Taken together, our results demonstrate that biofilm formation in clinical isolates of C. parapsilosis is both dependent and independent of BCR1, but even in strains which showed a BCR1-independent biofilm phenotype, BCR1 has alternative physiological functions.

Effect of tetrandrine against Candida albicans biofilms

Candida albicans is the most common human fungal pathogen and has a high propensity to develop biofilms that are resistant to traditional antifungal agents. In this study, we investigated the effect of tetrandrine (TET) on growth, biofilm formation and yeast-to-hypha transition of C. albicans. We characterized the inhibitory effect of TET on hyphal growth and addressed its possible mechanism of action. Treatment of TET at a low concentration without affecting fungal growth inhibited hyphal growth in both liquid and solid Spider media. Real-time RT-PCR revealed that TET down-regulated the expression of hypha-specific genes ECE1, ALS3 and HWP1, and abrogated the induction of EFG1 and RAS1, regulators of hyphal growth. Addition of cAMP restored the normal phenotype of the SC5314 strain. These results indicate that TET may inhibit hyphal growth through the Ras1p-cAMP-PKA pathway. In vivo, at a range of concentrations from 4 mg/L to 32 mg/L, TET prolonged the survival of C. albicans-infected Caenorhabditis elegans significantly. This study provides useful information for the development of new strategies to reduce the incidence of C. albicans biofilm-associated infections.

Candida albicans biofilm chip (CaBChip) for high-throughput antifungal drug screening

Candida albicans remains the main etiological agent of candidiasis, which currently represents the fourth most common nosocomial bloodstream infection in US hospitals. These opportunistic infections pose a growing threat for an increasing number of compromised individuals, and carry unacceptably high mortality rates. This is in part due to the limited arsenal of antifungal drugs, but also to the emergence of resistance against the most commonly used antifungal agents. Further complicating treatment is the fact that a majority of manifestations of candidiasis are associated with the formation of biofilms, and cells within these biofilms show increased levels of resistance to most clinically-used antifungal agents. Here we describe the development of a high-density microarray that consists of C. albicans nano-biofilms, which we have named CaBChip. Briefly, a robotic microarrayer is used to print yeast cells of C. albicans onto a solid substrate. During printing, the yeast cells are enclosed in a three dimensional matrix using a volume as low as 50 nL and immobilized on a glass substrate with a suitable coating. After initial printing, the slides are incubated at 37 °C for 24 hours to allow for biofilm development. During this period the spots grow into fully developed "nano-biofilms" that display typical structural and phenotypic characteristics associated with mature C. albicans biofilms (i.e. morphological complexity, three dimensional architecture and drug resistance). Overall, the CaBChip is composed of ~750 equivalent and spatially distinct biofilms; with the additional advantage that multiple chips can be printed and processed simultaneously. Cell viability is estimated by measuring the fluorescent intensity of FUN1 metabolic stain using a microarray scanner. This fungal chip is ideally suited for use in true high-throughput screening for antifungal drug discovery. Compared to current standards (i.e. the 96-well microtiter plate model of biofilm formation), the main advantages of the fungal biofilm chip are automation, miniaturization, savings in amount and cost of reagents and analyses time, as well as the elimination of labor intensive steps. We believe that such chip will significantly speed up the antifungal drug discovery process.

Biofilm Formation of Candida spp. Isolates from Patients at a Cardiothoracic Intensive Care Unit

Invasive Candida infections in seriously ill patients are rare but associated with high mortality, while Candida colonization of the mucocuteneous surfaces is common in patients admitted to intensive care units. To investigate biofilm formation as a possible virulence factor, we analyzed the biofilm formation of 128 non-invasive isolates from long-term ICU patients and that of 106 invasive bloodstream isolates. Candida biofilms were quantified by the percent transmittance (%Tbloc) method. Crystal Violet (CV) staining was used as marker of biofilm thickness, and XTT assay was used as a marker of the metabolic activity of Candida cells. The ability of biofilm formation was 99.2% in the non-invasive isolates versus 96.2% in the bloodstream isolates (%Tbloc vs.%Tbloc not significant). However, high biofilm production (%Tbloc, ≥35) was more frequent among the non-invasive isolates compared to the bloodstream isolates (78.1 vs. 72.5, p<0.001).