Effect of growth rate on resistance of Candida albicans biofilms to antifungal agents

A ketogenic diet enhances fluconazole efficacy in murine models of systemic fungal infection

Invasive fungal infections are a significant public health concern, with mortality rates ranging from 20% to 85% despite current treatments. Therefore, we examined whether a ketogenic diet could serve as a successful treatment intervention in murine models of Cryptococcus neoformans and Candida albicans infection in combination with fluconazole-a low-cost, readily available antifungal therapy. The ketogenic diet is a high-fat, low-carbohydrate diet that promotes fatty acid oxidation as an alternative to glycolysis through the production of ketone bodies. In this series of experiments, mice fed a ketogenic diet prior to infection with C. neoformans and treated with fluconazole had a significant decrease in fungal burden in both the brain (mean 2.66 ± 0.289 log10 reduction) and lung (mean 1.72 ± 0.399 log10 reduction) compared to fluconazole treatment on a conventional diet. During C. albicans infection, kidney fungal burden of mice in the keto-fluconazole combination group was significantly decreased compared to fluconazole alone (2.37 ± 0.770 log10-reduction). Along with higher concentrations of fluconazole in the plasma and brain tissue, fluconazole efficacy was maximized at a significantly lower concentration on a keto diet compared to a conventional diet, indicating a dramatic effect on fluconazole pharmacodynamics. Our findings indicate that a ketogenic diet potentiates the effect of fluconazole at multiple body sites during both C. neoformans and C. albicans infection and could have practical and promising treatment implications.IMPORTANCEInvasive fungal infections cause over 2.5 million deaths per year around the world. Treatments for fungal infections are limited, and there is a significant need to develop strategies to enhance antifungal efficacy, combat antifungal resistance, and mitigate treatment side effects. We determined that a high-fat, low-carbohydrate ketogenic diet significantly potentiated the therapeutic effect of fluconazole, which resulted in a substantial decrease in tissue fungal burden of both C. neoformans and C. albicans in experimental animal models. We believe this work is the first of its kind to demonstrate that diet can dramatically influence the treatment of fungal infections. These results highlight a novel strategy of antifungal drug enhancement and emphasize the need for future investigation into dietary effects on antifungal drug activity.

Antifungal drug resistance in Candida: a special emphasis on amphotericin B

Invasive fungal infections in humans caused by several Candida species, increased considerably in immunocompromised or critically ill patients, resulting in substantial morbidity and mortality. Candida albicans is the most prevalent species, although the frequency of these organisms varies greatly according to geographic region. Infections with C. albicans and non-albicans Candida species have become more common, especially in the past 20 years, as a result of aging, immunosuppressive medication use, endocrine disorders, malnourishment, extended use of medical equipment, and an increase in immunogenic diseases. Despite C. albicans being the species most frequently associated with human infections, C. glabrata, C. parapsilosis, C. tropicalis, and C. krusei also have been identified. Several antifungal drugs with different modes of action are approved for use in clinical settings to treat fungal infections. However, due to the common eukaryotic structure of humans and fungi, only a limited number of antifungal drugs are available for therapeutic use. Furthermore, drug resistance in Candida species has emerged as a result of the growing use of currently available antifungal drugs against fungal infections. Amphotericin B (AmB), a polyene class of antifungal drugs, is mainly used for the treatment of serious systemic fungal infections. AmB interacts with fungal plasma membrane ergosterol, triggering cellular ion leakage via pore formation, or extracting the ergosterol from the plasma membrane inducing cellular death. AmB resistance is primarily caused by changes in the content or structure of ergosterol. This review summarizes the antifungal drug resistance exhibited by Candida species, with a special focus on AmB.

Cellular Attributes of Candida albicans Biofilm-Associated in Resistance Against Multidrug and Host Immune System

One of the ubiquitous hospital-acquired infections is associated with Candida albicans fungus. Usually, this commensal fungus causes no harm to its human host, as it lives mutually with mucosal/epithelial tissue surface cells. Nevertheless, due to the activity of various immune weakening factors, this commensal starts reinforcing its virulence attributes with filamentation/hyphal growth and building an absolute microcolony composed of yeast, hyphal, and pseudohyphal cells, which is suspended in an extracellular gel-like polymeric substance (EPS) called biofilms. This polymeric substance is the mixture of the secreted compounds from C. albicans as well as several host cell proteins. Indeed, the presence of these host factors makes their identification and differentiation process difficult by host immune components. The gel-like texture of the EPS makes it sticky, which adsorbs most of the extracolonial compounds traversing through it that aid in penetration hindrance. All these factors further contribute to the multidrug resistance phenotype of C. albicans biofilm that is spotlighted in this article. The mechanisms it employs to escape the host immune system are also addressed effectively. The article focuses on cellular and molecular determinants involved in the resistance of C. albicans biofilm against multidrug and the host immune system.

Resistance profiles to antifungal agents in Candida albicans isolated from human oral cavities: systematic review and meta-analysis

Aim

To identify the antifungal susceptibility profile of Candida spp. isolated from the human oral cavity was assessed with meta-analyses of observational studies that collected samples from the oral cavity of human subjects.

Material and methods

Isolated Candida albicans tested by E-test®; disk diffusion test; microdilution and macrodilution; Sensititre YeastOne; and/or FungiTest. Search strategies were conducted on the MEDLINE, Embase, CINAHL, Dentistry, and Oral Sciences, Central, Scopus, and LILACS databases, and gray literature sources. Articles were initially screened by title and then their abstracts. Articles that met the conditions for inclusion were read in full, followed by data extraction. A descriptive analysis was conducted of each study, and the data were tabulated. A first meta-analysis was conducted to assess the resistance of antifungals regardless of systemic comorbidities. An additional stratified analysis was conducted by systemic comorbidity groups for the outcome “resistance” to the antifungals.

Results

When not grouping Candida albicans isolates by systemic conditions, the lowest resistance rates to the antifungals tested were observed for amphotericin B, nystatin, flucytosine, and caspofungin. In contrast, the highest resistance rates were observed for miconazole and econazole. There was a high degree of heterogeneity and low resistance in general in all analyses, except for the “several associated comorbidities” group, which had high resistance rates.

Conclusions

Clinical C. albicans isolates had low antifungal resistance.

Clinical relevance

The presence of concomitant systemic comorbidities appears to be an essential factor that should be considered when evaluating resistance to antifungals for oral isolates.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00784-022-04716-2.

Amphiphilic hyperbranched polyglycerol nanoarchitectures for Amphotericin B delivery in Candida infections

Although Amphotericin B (AMB) is considered the most effective anti-mycotic agent for treating Candida infections, its clinical use is limited due to its high toxicity. To address this issue, we developed cholesterol-based dendritic micelles of hyperbranched polyglycerol (HPG), including cholesterol-cored HPG (Chol-HPG) and cholesterol end-capped HPG (HPG@Chol), for AMB delivery. The findings suggested that the presence of cholesterol moieties could control AMB loading and release properties. Dendritic micelles inhibited AMB hemolysis and cytotoxicity in HEK 293 and RAW 264.7 cell lines while increasing antifungal activity against C. albicans biofilm formation. Furthermore, significantly lower levels of renal and liver toxicity biomarkers compared to Fungizone® ensured AMB-incorporated dendritic micelle biosafety, which was confirmed by histopathological evaluations. Overall, the Chol-HPG and HPG@Chol dendritic micelles may be a viable alternative to commercially available AMB formulations as well as an effective delivery system for other poorly soluble antifungal agents.

Antifungal Susceptibility of Candida albicans Isolated from Tongue and Subgingival Biofilm of Periodontitis Patients

The subgingival biofilm, as the most complex microbial community, has been proven to be reservoir of Candida spp. The main concept of this study was to investigate if there is a difference between the sensitivity of Candida albicans (C. albicans) isolated from tongue and subgingival areas of periodontitis patients to antifungal agents. The aim of the study was to determine: (1) the distribution of different Candida species in the tongue and subgingival samples of periodontitis patients; (2) the susceptibility of Candida albicans strains from tongue and subgingival biofilm to the effects of commonly used antifungal agents: fluconazole, amphotericin B and itraconazole; (3) the correlation between the susceptibility of Candida albicans and clinical periodontal parameters. Tongue and subgingival biofilm samples of periodontitis subjects (N = 163) were examined. Susceptibility was tested when the same Candida species was isolated from both sites (17 subjects). Candida spp. were isolated in 23.3% of tongue and 21.5% of the subgingival samples. All isolates were susceptible to amphotericin B, while 64.71% of tongue and 52.94% of subgingival isolates were susceptible to fluconazole. A low frequency of itraconazole susceptibility was observed for tongue (17.64%) and subgingival isolates (11.76%). The correlations between full-mouth plaque score and Minimal Inhibitory Concentration (MIC) for tongue isolates were strongly positive for all antimycotics. Positive correlation was also observed between moderate periodontal destruction and MICs for tongue and subgingival isolates. The susceptibility of C. albicans to antifungals correlate with oral hygiene and moderate periodontal destruction. There is no difference in antifungal susceptibility between tongue and subgingival isolates.

Antifungal Exposure and Resistance Development: Defining Minimal Selective Antifungal Concentrations and Testing Methodologies

This scoping review aims to summarise the current understanding of selection for antifungal resistance (AFR) and to compare and contrast this with selection for antibacterial resistance, which has received more research attention. AFR is an emerging global threat to human health, associated with high mortality rates, absence of effective surveillance systems and with few alternative treatment options available. Clinical AFR is well documented, with additional settings increasingly being recognised to play a role in the evolution and spread of AFR. The environment, for example, harbours diverse fungal communities that are regularly exposed to antifungal micropollutants, potentially increasing AFR selection risk. The direct application of effect concentrations of azole fungicides to agricultural crops and the incomplete removal of pharmaceutical antifungals in wastewater treatment systems are of particular concern. Currently, environmental risk assessment (ERA) guidelines do not require assessment of antifungal agents in terms of their ability to drive AFR development, and there are no established experimental tools to determine antifungal selective concentrations. Without data to interpret the selective risk of antifungals, our ability to effectively inform safe environmental thresholds is severely limited. In this review, potential methods to generate antifungal selective concentration data are proposed, informed by approaches used to determine antibacterial minimal selective concentrations. Such data can be considered in the development of regulatory guidelines that aim to reduce selection for AFR.

Effects of Methyl, Ester, and Amine Surface Groups on Microbial Activity and Communities in Nitrifying Biofilms

The objective of this study was to determine how different attachment surface chemistries affected the initial and long-term performance and microbial populations of nitrifying biofilms under well-controlled hydrodynamic mixing conditions. While much previous research has focused on the effects of surface properties such as hydrophobicity on bacterial attachment in pure cultures, this study evaluated the effects of specific functional groups on mixed culture composition and functional behavior. Three surfaces with varying hydrophobicity and charge were evaluated for biofilm community development and performance: unmodified poly(dimethylsiloxane) (PDMS), which included terminal methyl groups and was relatively hydrophobic (P-Methyl), PDMS silanized with ester groups (P-Ester), which was uncharged and relatively hydrophilic, and PDMS modified with amine groups (P-Amine), which possessed a positive charge and was the most hydrophilic. The surface chemistries of the three attachment surfaces were characterized by contact angle goniometry, Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). These surfaces were inoculated with dilute activated sludge, and biofilms were grown in rotating annular bioreactors for 80 days, with experimental triplicates. Nitrification rates increased most rapidly in P-Amine biofilm reactors, and their biofilm communities contained significantly more Nitrosomonas (p < 0.05) than those on the other surfaces in early growth stages (days 40-50). From days 50-60, the P-Amine surface biofilm had significantly higher nitrate production rates than the P-Methyl and P-Ester biofilms. The biofilms grown on the P-Amine and P-Methyl surfaces were significantly (p < 0.05) more diverse than the P-Ester biofilms, containing higher relative abundances of the order Rhizobiales, including a significantly higher abundance of the nitrifying genus Nitrobacter (p < 0.05), which coincided with higher rates of nitrate generation. Conversely, biofilms grown on the uncharged hydrophilic P-Ester surface were consistently less productive and had lower diversity than biofilms on the other surfaces. These results indicate that surface chemistry may be a useful design parameter to improve the performance of nitrifying biofilm systems for wastewater treatment and that surface chemistry affects mixed biofilm community composition.

Virulence Factors as Promoters of Chronic Vulvovaginal Candidosis: A Review

INTRODUCTION

The vast majority of the species of the genus Candida spp. is commensal in humans; however, some are opportunistic pathogens that can cause infection, called candidosis. Among the different types of candidosis, we highlight the vulvovaginal (VVC) which can occur in two main clinical variants: chronic (cVVC) and episodic or sporadic. The incidence of cVVC has been worrying the scientific community, promoting the research on genotypic and phenotypic causes of its occurrence. We summarize important findings on factors that favor chronic vulvovaginal candidosis with respect to molecular epidemiology and the expression of various virulence factors, while clarifying the terminology involving these infections.

AIM AND METHODOLOGY

The aim of this review was to gather research that linked virulence factors to VVC and its persistence and recurrence, using two databases (Pubmed and Google Scholar). Predisposing factors in women for the occurrence of cVVC and some studies that refer new preventive and alternative therapies were also included, where appropriate.

RESULTS AND DISCUSSION

Several studies have been shedding light on the increasing number of persistence and recurrences of VVC. The expression of virulence factors has been related to both chronic forms of VVC and antifungal resistance. Other studies report mutations occurring in the genome of Candida spp. during the infection phase which may be important indications for new therapies. The introduction of preventive therapies and new therapies has revealed great importance and is also highlighted here.

Development of a novel denture care agent with highly active enzyme, arazyme

BACKGROUND

The importance of efficient denture deposit removal and oral hygiene has been further underscored by the continuous increase of denture wearers. Denture hygiene management has also become an important aspect associated with denture-induced stomatitis. This study aims to evaluate the denture cleaning effect of arazyme, the metalloprotease produced from the Serratia proteamaculans HY-3. We performed growth inhibition tests against oral opportunistic pathogens to be used as a potential oral health care agent.

METHODS

The proteolytic activities of arazyme was evaluated over broad ranges of temperature, pH, and denture components compared to those of subtilisin in commercially available denture cleansers. The washing effects of arazyme were also measured by using homogeneously soiled EMPA 105 cottons. To investigate the denture cleaning capability of arazyme, artificially contaminated dentures were treated with arazyme, subtilisin (Everlase 6.0T), and Polident®, respectively. The growth kinetics of Candida albicans, Enterococcus faecalis, Staphylococcus epidermis, and Streptococcus mutans were evaluated in the presence of different concentrations of arazyme to estimate the prevention effects of arazyme against major oral opportunistic pathogens.

RESULTS

Arazyme showed strong proteolytic activities over wide temperature and pH ranges compared with the serine protease of the subtilisin family. Arazyme demonstrated efficient removal and decomposition of artificially contaminated dentures and showed explicit washing effects against soiled cottons. Moreover arazyme inhibited the growth of oral opportunistic pathogens, including C. albicans, E. faecalis, S. epidermis, and S. mutans, with more than 80% inhibition against C. albicans, the major cause of denture stomatitis, with 250 mg/mL arazyme.

CONCLUSIONS

Arazyme shows promise as a biological oral health care agent with effective cleaning and antimicrobial activities and is a potential source for developing novel denture care agents.

Computational Drug Repurposing Resources and Approaches for Discovering Novel Antifungal Drugs against Candida albicans N-Myristoyl Transferase

Candida albicans is a yeast that is an opportunistic fungal pathogen and also identified as ubiquitous polymorphic species that is mainly linked with major fungal infections in humans, particularly in the immunocompromised patients including transplant recipients, chemotherapy patients, HIV-infected patients as well as in low-birth-weight infants. Systemic Candida infections have a high mortality rate of around 29 to 76%. For reducing its infection, limited drugs are existing such as caspofungin, fluconazole, terbinafine, and amphotericin B, etc. which contain unlikable side effects and also toxic. This review intends to utilize advanced bioinformatics technologies such as Molecular docking, Scaffold hopping, Virtual screening, Pharmacophore modeling, Molecular dynamics (MD) simulation for the development of potentially new drug candidates with a drug-repurpose approach against Candida albicans within a limited time frame and also cost reductive.

Sixty years of Amphotericin B: An Overview of the Main Antifungal Agent Used to Treat Invasive Fungal Infections

Introduced in the late 1950s, polyenes represent the oldest family of antifungal drugs. The discovery of amphotericin B and its therapeutic uses is considered one of the most important scientific milestones of the twentieth century . Despite its toxic potential, it remains useful in the treatment of invasive fungal diseases owing to its broad spectrum of activity, low resistance rate, and excellent clinical and pharmacological action. The well-reported and defined toxicity of the conventional drug has meant that much attention has been paid to the development of new products that could minimize this effect. As a result, lipid-based formulations of amphotericin B have emerged and, even keeping the active principle in common, present distinct characteristics that may influence therapeutic results. This study presents an overview of the pharmacological properties of the different formulations for systemic use of amphotericin B available for the treatment of invasive fungal infections, highlighting the characteristics related to their chemical, pharmacokinetic structures, drug–target interactions, stability, and others, and points out the most relevant aspects for clinical practice.

Biofilm of Candida albicans: formation, regulation and resistance

Candida albicans is the most common human fungal pathogen, causing infections that range from mucous membranes to systemic infections. The present article provides an overview of C. albicans, with the production of biofilms produced by this fungus, as well as reporting the classes of antifungals used to fight such infections, together with the resistance mechanisms to these drugs. Candida albicans is highly adaptable, enabling the transition from commensal to pathogen due to a repertoire of virulence factors. Specifically, the ability to change morphology and form biofilms is central to the pathogenesis of C. albicans. Indeed, most infections by this pathogen are associated with the formation of biofilms on surfaces of hosts or medical devices, causing high morbidity and mortality. Significantly, biofilms formed by C. albicans are inherently tolerant to antimicrobial therapy, so the susceptibility of C. albicans biofilms to current therapeutic agents remains low. Therefore, it is difficult to predict which molecules will emerge as new clinical antifungals. The biofilm formation of C. albicans has been causing impacts on susceptibility to antifungals, leading to resistance, which demonstrates the importance of research aimed at the prevention and control of these clinical microbial communities.

Inhibitory Effect of Morin Against Candida albicans Pathogenicity and Virulence Factor Production: An in vitro and in vivo Approaches

Candida albicans is considered an exclusive etiologic agent of candidiasis, a very common fungal infection in human. The expression of virulence factors contributes highly to the pathogenicity of C. albicans. These factors include biofilm formation, yeast-to-hyphal transition, adhesins, aspartyl proteases, and phospholipases secretion. Moreover, resistance development is a critical issue for the therapeutic failure of antifungal agents against systemic candidiasis. To circumvent resistance development, the present study investigated the virulence targeted therapeutic activity of the phyto-bioactive compound morin against C. albicans. Morin is a natural compound commonly found in medicinal plants and widely used in the pharmaceutical and cosmetic products/industries. The present study explicated the significant inhibitory potential of morin against biofilm formation and other virulence factors' production, such as yeast-hyphal formation, phospholipase, and exopolymeric substances, in C. albicans. Further, qPCR analysis confirmed the downregulation of biofilm and virlence-related genes in C. albicans upon morin treatment, which is in correspondence with the in vitro bioassays. Further, the docking analysis revealed that morin shows strong affinity with Hwp-1 protein, which regulates the expression of biofilm and hyphal formation in C. albicans and, thereby, abolishes fungal pathogenicity. Moreover, the anti-infective potential of morin against C. albicans-associated systemic candidiasis is confirmed through an in vivo approach using biomedical model organism zebrafish (Danio rerio). The outcomes of the in vivo study demonstrate that the morin treatment effectively rescues animals from C. albicans infections and extends their survival rate by inhibiting the internal colonization of C. albicans. Histopathology analysis revealed extensive candidiasis-related pathognomonic changes in the gills, intestine, and kidney of animals infected with C. albicans, while no extensive abnormalities were observed in morin-treated animals. The results evidenced that morin has the ability to protect against the pathognomonic effect and histopathological lesions caused by C. albicans infection in zebrafish. Thus, the present study suggests that the utilization of morin could act as a potent therapeutic medication for C. albicans instigated candidiasis.

Effects of two peroxide enzymatic denture cleaners on Candida albicans biofilms and denture surface

Objective

To compare the antifungal action of two commercially available denture cleaning agents to that of standard clinical solutions, and determine their effects on the polymethyl methacrylate (PMMA) acrylic resin denture surface.

Methods

Candida albicans growth was analyzed by colony forming assay, and the methyl thiazolyl tetrazolium (MTT) assay was used to evaluate biofilm formation and cell adhesion. The morphology and roughness of PMMA acrylic resin surface was measured by scanning electron microscopy (SEM) images and stylus method.

Results

Clene®, Polident® and 3% NaHCO₃ solutions showed significantly greater antifungal effects in terms of both inhibiting growth and biofilm formation. In addition, Clene® solution prevented adhesion of C. albicans on cell culture plates compared to filter-sterile tap water, whereas other reagents did not have an inhibitory effect. One-month immersion in the different cleaning reagents significantly inhibited fungal adhesion on the PMMA surface Clene®, Polident® and 3% NaHCO₃ showed greater effect compared to PBS and filter-sterile tap water. Finally, none of the cleansing agents significantly affected the morphology and roughness of the PMMA surface.

Conclusion

Clene®, Polident® and 3% NaHCO₃ solutions can inhibit C. albicans growth and biofilm formation to some extent on cell culture plates, and significantly inhibit fungal adhesion on the PMMA surface without affecting surface morphology and roughness.

Relationship between antifungal susceptibility profile and virulence factors in Candida albicans isolated from nail specimens

INTRODUCTION

The aim of this study was to evaluate some virulence factors in Candida albicans isolates from patients with onychomycosis and determine the correlation between these factors and the antifungal resistance profile.

METHODS

Seventy species of C. albicans were confirmed using polymerase chain reaction amplification of the HWP1 gene. According to the Clinical & Laboratory Standards Institute guidelines, the susceptibility profile of four antifungal agents was investigated, and the production of aspartyl protease, phospholipase, haemolysin, and biofilm was determined. The correlation between these profiles was also investigated.

RESULTS

The isolates indicated different levels of resistance and production of virulence factors. Significant correlations were observed between the minimum inhibitory concentration (MIC) of fluconazole/itraconazole and biofilm production, between phospholipase production and fluconazole/itraconazole MIC, and between fluconazole MIC and hemolytic activity in C. albicans isolates. The results also showed significant correlations between phospholipase activity and biofilm production.

CONCLUSIONS

Our findings will contribute to a better understanding of the pathogenesis of C. albicans and characterize the relationship between virulence factors and antifungal resistance, which may suggest new therapeutic strategies considering the possible involvement of the virulence mechanism in the effectiveness of treatment.

Drug-mediated metabolic tipping between antibiotic resistant states in a mixed-species community

Microbes rarely exist in isolation, rather, they form intricate multi-species communities that colonize our bodies and inserted medical devices. However, the efficacy of antimicrobials is measured in clinical laboratories exclusively using microbial monocultures. Here, to determine how multi-species interactions mediate selection for resistance during antibiotic treatment, particularly following drug withdrawal, we study a laboratory community consisting of two microbial pathogens. Single-species dose responses are a poor predictor of community dynamics during treatment so, to better understand those dynamics, we introduce the concept of a dose-response mosaic, a multi-dimensional map that indicates how species' abundance is affected by changes in abiotic conditions. We study the dose-response mosaic of a two-species community with a 'Gene × Gene × Environment × Environment' ecological interaction whereby Candida glabrata, which is resistant to the antifungal drug fluconazole, competes for survival with Candida albicans, which is susceptible to fluconazole. The mosaic comprises several zones that delineate abiotic conditions where each species dominates. Zones are separated by loci of bifurcations and tipping points that identify what environmental changes can trigger the loss of either species. Observations of the laboratory communities corroborated theory, showing that changes in both antibiotic concentration and nutrient availability can push populations beyond tipping points, thus creating irreversible shifts in community composition from drug-sensitive to drug-resistant species. This has an important consequence: resistant species can increase in frequency even if an antibiotic is withdrawn because, unwittingly, a tipping point was passed during treatment.

Chestnut Honey and Bacteriophage Application to Control Pseudomonas aeruginosa and Escherichia coli Biofilms: Evaluation in an ex vivo Wound Model

Chronic skin wounds represent a major burn both economically and socially. Pseudomonas aeruginosa and Escherichia coli are among the most common colonizers of infected wounds and are prolific biofilm formers. Biofilms are a major problem in infections due to their increasingly difficult control and eradication, and tolerance to multiple prescribed drugs. As so, alternative methods are necessary. Bacteriophages (phages) and honey are both seen as a promising approach for biofilm related infections. Phages have specificity toward a bacterial genus, species or even strain, self-replicating nature, and avoid dysbiosis. Honey has gained acknowledgment due to its antibacterial, antioxidant and anti-inflammatory and wound healing properties. In this work, the effect of E. coli and P. aeruginosa phages vB_EcoS_CEB_EC3a and vB_PaeP_PAO1-D and chestnut honey, alone and combined, were tested using in vitro (polystyrene) and ex vivo (porcine skin) models and against mono and dual-species biofilms of these bacteria. In general, colonization was higher in the porcine skins and the presence of a second microorganism in a consortium of species did not affect the effectiveness of the treatments. The antibacterial effect of combined therapy against dual-species biofilms led to bacterial reductions that were greater for biofilms formed on polystyrene than on skin. Monospecies biofilms of E. coli were better destroyed with phages and honey than P. aeruginosa monospecies biofilms. Overall, the combined phage-honey formulations resulted in higher efficacies possibly due to honey's capacity to damage the bacterial cell membrane and also to its ability to penetrate the biofilm matrix, promoting and enhancing the subsequent phage infection.

In Vitro Evaluation of the Inhibitory Activity of Thymoquinone in Combatting Candida albicans in Denture Stomatitis Prevention

Candida albicans adhesion and proliferation on denture bases may lead to denture stomatitis, which is a common and recurrent problem in denture wearers. The goal of this study was to assess the inhibitory effect of thymoquinone incorporated in the polymethyl methacrylate denture base material against Candida albicans. Eighty acrylic resin specimens were fabricated and divided into eight groups (n = 10) according to thymoquinone concentrations of 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, and 5% of acrylic powder. Two methods were used to evaluate the effect of thymoquinone on Candida albicans: the slide count and the serial dilution test. A multivariate analysis of variance (MANOVA) and the post-hoc Tukey’s Honestly Significant Difference (HSD) test were performed to compare the difference of means between the observations taken at various intervals with baseline. The p value was statistically significant at ≤0.05. According to the slide count and the serial dilution test, the mean number of adhered Candida albicans in the control group was 5436.9 ± 266 and 4691.4 ± 176.8; however, this number dramatically decreased to 0 ± 0 and 32.4 ± 1.7 in group 8 (concentration 5%). These results suggest that the incorporation of thymoquinone into the acrylic resin denture base material might be effective in preventing Candida albicans adhesion.

Efficiency of four currently used decontamination conditionings in Romania against Aspergillus and Candida strains

INTRODUCTION

Efficacy of four commercial biocidal products (noted A to D), using manufacturers' recommendations, and a contact time of 30minutes, were evaluated in the purpose of standard SR EN1657: 2006 adapted.

METHODS

Were used four strains, two as reference: Aspergillus brasiliensis (niger) (ATCC 16404) and Candida albicans (ATCC 10231), and two isolates: Aspergillus flavus and respectively Aspergillus fumigatus. The inoculum plates containing Malt Extract Agar (MEA) were incubated 48h for C. albicans and 72hours for Aspergillus spp. The standard SR EN1657: 2006 adapted was conducted in two phases: the test cultures preparation and the method validation. Method validation included: the control of experimental conditions and of neutralizant solution, and the method verification.

RESULTS

Results revealed that three from the four tested products (A, B and D) had exerted biocidal effect on the studied strains at the recommended concentrations, the registered CFU values being reduced by more than 4 log₁₀, conversely in the case of the product (C), applied against A. fumigatus at the recommended concentration of 2%, the biocidal effect was not detected, fact confirmed also by the CFU's value (3.59 log₁₀). The biocide retested at a greater concentration (of 5%), showed a biocidal effect against A. fumigatus after 30minutes, the CFU value being reduced, by more than 5.29 log₁₀, evidencing the resistance emergence of A. fumigatus under the repeated pressure of biocides.

CONCLUSION

It is re-confirming that merely the "chemical" defense measures to defuse the fungi's strategies become unproductive.

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.

Candida Species Biofilms' Antifungal Resistance

Candida infections (candidiasis) are the most prevalent opportunistic fungal infection on humans and, as such, a major public health problem. In recent decades, candidiasis has been associated to Candida species other than Candida albicans. Moreover, biofilms have been considered the most prevalent growth form of Candida cells and a strong causative agent of the intensification of antifungal resistance. As yet, no specific resistance factor has been identified as the sole responsible for the increased recalcitrance to antifungal agents exhibited by biofilms. Instead, biofilm antifungal resistance is a complex multifactorial phenomenon, which still remains to be fully elucidated and understood. The different mechanisms, which may be responsible for the intrinsic resistance of Candida species biofilms, include the high density of cells within the biofilm, the growth and nutrient limitation, the effects of the biofilm matrix, the presence of persister cells, the antifungal resistance gene expression and the increase of sterols on the membrane of biofilm cells. Thus, this review intends to provide information on the recent advances about Candida species biofilm antifungal resistance and its implication on intensification of the candidiasis.

Pathogenesis of Candida albicans biofilm

Candida albicans is the most common human fungal pathogen causing diseases ranging from mucosal to systemic infections. As a commensal, C. albicans asymptomatically colonizes mucosal surfaces; however, any disruption in the host environment or under conditions of immune dysfunction, C. albicans can proliferate and invade virtually any site in the host. The ability of this highly adaptable fungal species to transition from commensal to pathogen is due to a repertoire of virulence factors. Specifically, the ability to switch morphology and form biofilms are properties central to C. albicans pathogenesis. In fact, the majority of C. albicans infections are associated with biofilm formation on host or abiotic surfaces such as indwelling medical devices, which carry high morbidity and mortality. Significantly, biofilms formed by C. albicans are inherently tolerant to antimicrobial therapy and therefore, the susceptibility of Candida biofilms to the current therapeutic agents remains low. The aim of this review is to provide an overview of C. albicans highlighting some of the diverse biofilm-associated diseases caused by this opportunistic pathogen and the animal models available to study them. Further, the classes of antifungal agents used to combat these resilient infections are discussed along with mechanisms of drug resistance.

Large-scale production and isolation of Candida biofilm extracellular matrix

The extracellular matrix of biofilm is unique to the biofilm lifestyle, and it has key roles in community survival. A complete understanding of the biochemical nature of the matrix is integral to the understanding of the roles of matrix components. This knowledge is a first step toward the development of novel therapeutics and diagnostics to address persistent biofilm infections. Many of the assay methods needed for refined matrix composition analysis require milligram amounts of material that is separated from the cellular components of these complex communities. The protocol described here explains the large-scale production and isolation of the Candida biofilm extracellular matrix. To our knowledge, the proposed procedure is the only currently available approach in the field that yields milligram amounts of biofilm matrix. This procedure first requires biofilms to be seeded in large-surface-area roller bottles, followed by cell adhesion and biofilm maturation during continuous movement of the medium across the surface of the rotating bottle. The formed matrix is then separated from the entire biomass using sonication, which efficiently removes the matrix without perturbing the fungal cell wall. Subsequent filtration, dialysis and lyophilization steps result in a purified matrix product sufficient for biochemical, structural and functional assays. The overall protocol takes ∼11 d to complete. This protocol has been used for Candida species, but, using the troubleshooting guide provided, it could be adapted for other fungi or bacteria.

Antimicrobial potential of two traditional herbometallic drugs against certain pathogenic microbial species

Background

Mineral based preparations are widely used for centuries as antimicrobial agents. However, the efficacy and the mode of action of mineral based preparations are uncertain due to the insufficient antimicrobial studies. Arogyawardhana Vati (AV) and Manikya Rasa (MR) are such two Rasashastra herbo-minerallic drugs commonly in India and other countries in South Asia. Despite of their well known traditional use of skin diseases, reported antimicrobial and mineralogical studies are limited. Therefore, in this study antimicrobial activities of the drugs and their organic, inorganic fractions were evaluated against Pseudomonas aeruginosa, Escherischia coli, Staphylococcus aureus, Methecilline Resistance Staphylococcus aureus - MRSA and Candida albicans.

Methods

Antimicrobial activity of the drugs, their inorganic residues and organic extracts were determined using four assay techniques viz agar well diffusion, modified well diffusion, Miles and Misra viable cell counting and broth turbidity measurements. Mineralogical constituents of the drugs were determined using X-ray diffraction, while total cation constituents and water soluble cation constituents were determined using inductively coupled plasma-mass spectrometer and the atomic absorption spectrophotometer respectively. Thermogravimetric analysis was used to determine the weight percentages of organic and inorganic fraction of the drugs. Particle sizes of the drugs were determined using the particle size analyzer.

Results

AV and MR drugs showed antibacterial activity against both gram positive and gram negative bacterial species when analyzed separately. Inorganic residues of the drugs and organic extracts showed activity at least against two or more bacterial species tested. All tested components were inactive against C. albicans. Common mineral constituents of drugs are cinnabar, biotite and Fe-rich phases. Drugs were rich in essential elements such as Na, K, Ca, Mg and Fe and toxic elements such as Zn, Cu and As. However, the water soluble concentrations of the toxic elements were below the detection limits. Both drugs have significantly higher percentages of organic constituents and volatile minerals and particle sizes of drugs are in the nanometer range.

Conclusions

AV and MR Rasashastra preparations could provide alternatives to synthetic antibiotics against human bacterial infections. Improved solubility and reduced particle sizes are influential physicochemical properties used to enhance the antimicrobial efficacy of the drugs. Therefore, traditional knowledge on the use of antimicrobial mineral sources could provide a novel path for the producing of effective antimicrobial drugs. However, further chemical and toxicological studies are urgently needed for a greater understanding of their toxicity to humans.

Magnetic nanoparticles as a drug delivery system that enhance fungicidal activity of polyene antibiotics

This study was designed to assess the antifungal/anti-biofilm and hemolytic properties of two polyene antibiotics, amphotericin B (AMF) and nystatin (NYS), attached to the surface of magnetic nanoparticles (MNP) against clinical isolates of Candida species and human red blood cells, respectively. The developed nanosystems, MNP@AMF and MNP@NYS, displayed stronger fungicidal activity than unbound AMF or NYS. Synergistic activity was observed with a combination of polyenes and MNPs against all tested Candida strains. Nanosystems were more potent than unbound agents when tested against Candida strains in the presence of pus, and as agents able to prevent Candida biofilm formation. The observed inactivation of catalase Cat1 in Candida cells upon treatment with the nanosystems suggests that disruption of the oxidation-reduction balance is a mechanism leading to inhibition of Candida growth. The significant decrease of polyenes lytic activity against host cells after their attachment to MNPs surface indicates improvement in their biocompatibility.

Effect of Voriconazole on Candida tropicalis Biofilms: Relation with ERG Genes Expression

Candida tropicalis has emerged as the third most prevalent fungal pathogens and its ability to form biofilms has been considered one of the most important virulence factors, since biofilms represent high tolerance to antifungal agents. However, the mechanisms of C. tropicalis biofilm resistance to antifungals remain poorly understood. Thus, the main aim of this work was to infer about the effect of voriconazole on the formation and control of C. tropicalis biofilms and disclose its relationship with ERG genes' expression. Planktonic cells tolerance of several C. tropicalis clinical isolates to voriconazole was determined through of antifungal susceptibility test, and the effect of this azole against C. tropicalis biofilm formation and pre-formed biofilms was evaluated by cultivable cells determination and total biomass quantification. ERG genes expression was analyzed by quantitative real-time polymerase chain reaction. This work showed that C. tropicalis resistance to voriconazole is strain dependent and that voriconazole was able to partially control biofilm formation, but was unable to eradicate C. tropicalis pre-formed biofilms. Moreover, C. tropicalis biofilms resistance to voriconazole seems to be associated with alterations of sterol content in the cell membrane, resulting in ERG genes overexpression. Voriconazole is unable to control C. tropicalis biofilms, and the overexpression of ERG genes is a possible mechanism of biofilm resistance.

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.

Fungal Biofilms: In Vivo Models for Discovery of Anti-Biofilm Drugs

During infection, fungi frequently transition to a biofilm lifestyle, proliferating as communities of surface-adherent aggregates of cells. Phenotypically, cells in a biofilm are distinct from free-floating cells. Their high tolerance of antifungals and ability to withstand host defenses are two characteristics that foster resilience. Biofilm infections are particularly difficult to eradicate, and most available antifungals have minimal activity. Therefore, the discovery of novel compounds and innovative strategies to treat fungal biofilms is of great interest. Although many fungi have been observed to form biofilms, the most well-studied is Candida albicans. Animal models have been developed to simulate common Candida device-associated infections, including those involving vascular catheters, dentures, urinary catheters, and subcutaneous implants. Models have also reproduced the most common mucosal biofilm infections: oropharyngeal and vaginal candidiasis. These models incorporate the anatomical site, immune components, and fluid dynamics of clinical niches and have been instrumental in the study of drug resistance and investigation of novel therapies. This chapter describes the significance of fungal biofilm infections, the animal models developed for biofilm study, and how these models have contributed to the development of new strategies for the eradication of fungal biofilm infections.

Candida albicans Amphotericin B-Tolerant Persister Formation is Closely Related to Surface Adhesion

Candida albicans persisters have so far been observed only in biofilm environment; the biofilm element(s) that trigger(s) persister formation are still unknown. In this study, we tried to further elucidate the possible relationship between C. albicans persisters and the early phases of biofilm formation, especially the surface adhesion phase. Three C. albicans strains were surveyed for the formation of persisters. We tested C. albicans persister formation dynamically at different time points during the process of adhesion and biofilm formation. The number of persister cells was determined based on an assessment of cell viability after amphotericin B treatment and colony-forming unit assay. None of the planktonic cultures contained persisters. Immediately following adhesion of C. albicans cells to the surface, persister cells emerged and the proportion of persisters reached a peak of 0.2-0.69 % in approximately 2-h biofilm. As the biofilm matured, the proportion of persisters decreased and was only 0.01-0.02 % by 24 h, while the number of persisters remained stable with no significant change. Persisters were not detected in the absence of an attachment surface which was pre-coated. Persisters were also absent in biofilms that were scraped to disrupt surface adhesion prior to amphotericin B treatment. These results indicate that C. albicans antifungal-tolerant persisters are produced mainly in surface adhesion phase and surface adhesion is required for the emergence and maintenance of C. albicans persisters.

Growth, biofilm formation, antifungal susceptibility and oxidative stress resistance of Candida glabrata are affected by different glucose concentrations

Glucose is an important fuel source to support many living organisms. Its importance in the physiological fitness and pathogenicity of Candida glabrata, an emerging human fungal pathogen has not been extensively studied. The present study aimed to investigate the effects of glucose on the growth, biofilm formation, antifungal susceptibility and oxidative stress resistance of C. glabrata. In addition, its effect on the expression of a putative high affinity glucose sensor gene, SNF3 was also investigated. Glucose concentrations were found to exert effects on the physiological responses of C. glabrata. The growth rate of the species correlated positively to the amount of glucose. In addition, low glucose environments were found to induce C. glabrata to form biofilm and resist amphotericin B. Conversely, high glucose environments promoted oxidative stress resistance of C. glabrata. The expression of CgSNF3 was found to be significantly up-regulated in low glucose environments. The expression of SNF3 gene in clinical isolates was found to be higher compared to ATCC laboratory strains in low glucose concentrations, which may explain the better survivability of clinical isolates in the low glucose environment. These observations demonstrated the impact of glucose in directing the physiology and virulence fitness of C. glabrata through the possible modulation by SNF3 as a glucose sensor, which in turn aids the species to adapt, survive and thrive in hostile host environment.

Candida glabrata susceptibility to antifungals and phagocytosis is modulated by acetate

Candida glabrata is considered a major opportunistic fungal pathogen of humans. The capacity of this yeast species to cause infections is dependent on the ability to grow within the human host environment and to assimilate the carbon sources available. Previous studies have suggested that C. albicans can encounter glucose-poor microenvironments during infection and that the ability to use alternative non-fermentable carbon sources, such as carboxylic acids, contributes to the virulence of this fungus. Transcriptional studies on C. glabrata cells identified a similar response, upon nutrient deprivation. In this work, we aimed at analyzing biofilm formation, antifungal drug resistance, and phagocytosis of C. glabrata cells grown in the presence of acetic acid as an alternative carbon source. C. glabrata planktonic cells grown in media containing acetic acid were more susceptible to fluconazole and were better phagocytosed and killed by macrophages than when compared to media lacking acetic acid. Growth in acetic acid also affected the ability of C. glabrata to form biofilms. The genes ADY2a, ADY2b, FPS1, FPS2, and ATO3, encoding putative carboxylate transporters, were upregulated in C. glabrata planktonic and biofilm cells in the presence of acetic acid. Phagocytosis assays with fps1 and ady2a mutant strains suggested a potential role of FPS1 and ADY2a in the phagocytosis process. These results highlight how acidic pH niches, associated with the presence of acetic acid, can impact in the treatment of C. glabrata infections, in particular in vaginal candidiasis.

Candida Biofilms: Development, Architecture, and Resistance

Intravascular device-related infections are often associated with biofilms (microbial communities encased within a polysaccharide-rich extracellular matrix) formed by pathogens on the surfaces of these devices. Candida species are the most common fungi isolated from catheter-, denture-, and voice prosthesis-associated infections and also are commonly isolated from contact lens-related infections (e.g., fungal keratitis). These biofilms exhibit decreased susceptibility to most antimicrobial agents, which contributes to the persistence of infection. Recent technological advances have facilitated the development of novel approaches to investigate the formation of biofilms and identify specific markers for biofilms. These studies have provided extensive knowledge of the effect of different variables, including growth time, nutrients, and physiological conditions, on biofilm formation, morphology, and architecture. In this article, we will focus on fungal biofilms (mainly Candida biofilms) and provide an update on the development, architecture, and resistance mechanisms of biofilms.

Host-pathogen interactions between the human innate immune system and Candida albicans-understanding and modeling defense and evasion strategies

The diploid, polymorphic yeast Candida albicans is one of the most important human pathogenic fungi. C. albicans can grow, proliferate and coexist as a commensal on or within the human host for a long time. However, alterations in the host environment can render C. albicans virulent. In this review, we describe the immunological cross-talk between C. albicans and the human innate immune system. We give an overview in form of pairs of human defense strategies including immunological mechanisms as well as general stressors such as nutrient limitation, pH, fever etc. and the corresponding fungal response and evasion mechanisms. Furthermore, Computational Systems Biology approaches to model and investigate these complex interactions are highlighted with a special focus on game-theoretical methods and agent-based models. An outlook on interesting questions to be tackled by Systems Biology regarding entangled defense and evasion mechanisms is given.

Elimination of Bloodstream Infections Associated with Candida albicans Biofilm in Intravascular Catheters

Intravascular catheters are among the most commonly inserted medical devices and they are known to cause a large number of catheter related bloodstream infections (BSIs). Biofilms are associated with many chronic infections due to the aggregation of microorganisms. One of these organisms is the fungus Candida albicans. It has shown to be one of the leading causes of catheter-related BSIs. The presence of biofilm on intravascular catheters provide increased tolerance against antimicrobial treatments, thus alternative treatment strategies are sought. Traditionally, many strategies, such as application of combined antimicrobials, addition of antifungals, and removal of catheters, have been practiced, but they were not successful in eradicating BSIs. Since these fungal infections can result in significant morbidity, mortality, and increased healthcare cost, other promising preventive strategies, including antimicrobial lock therapy, chelating agents, alcohol, and biofilm disruptors, have been applied. In this review, current success and failure of these new approaches, and a comparison with the previous strategies are discussed in order to understand which preventative treatment is the most effective in controlling the catheter-related BSIs.

Self-assembled amphotericin B-loaded polyglutamic acid nanoparticles: preparation, characterization and in vitro potential against Candida albicans

In the present study, we developed a self-assembled biodegradable polyglutamic acid (PGA)-based formulation of amphotericin B (AmB) and evaluated its in vitro antifungal potential against Candida albicans. The AmB-loaded PGA nanoparticles were prepared in-house and had a mean size dimension of around 98±2 nm with a zeta potential of -35.2±7.3 mV. Spectroscopic studies revealed that the drug predominantly acquires an aggregated form inside the formulation with an aggregation ratio above 2. The PGA-based AmB formulation was shown to be highly stable in phosphate-buffered saline as well as in serum (only 10%-20% of the drug was released after 10 days). The AmB-PGA nanoparticles were less toxic to red blood cells (<15% lysis at an AmB concentration of 100 μg/mL after 24 hours) when compared with Fungizone(®), a commercial antifungal product. An MTT assay showed that the viability of mammalian cells (KB and RAW 264.7) was negligibly affected at AmB concentrations as high as 200 μg/mL. Histopathological examination of mouse kidney revealed no signs of tissue necrosis. The AmB-PGA formulation showed potent antimicrobial activity similar to that of Fungizone against C. albicans. Interestingly, AmB-bearing PGA nanoparticles were found to inhibit biofilm formation to a considerable extent. In summary, AmB-PGA nanoparticles showed highly attenuated toxicity when compared with Fungizone, while retaining equivalent active antifungal properties. This study indicates that the AmB-PGA preparation could be a promising treatment for various fungal infections.

Quantitative analysis of biofilm formation by oropharyngeal Candida albicans isolates under static conditions by confocal

Candida albicans may colonize natural or artificial surfaces, leading to formation of the biofilm. Infections associated with the biofilm formation are important therapeutic problem. In this paper, we present data concerning the biofilm formation under static conditions by oropharyngeal isolates of C. albicans on a glass surface using confocal scanning laser microscopy (CSLM). The areal parameters describing the architecture of biofilm and its development, i.e. the areal porosity, the length of edge line, the length of skeleton line, were calculated. The changes in values of these parameters during the biofilm formation by C. albicans were similar for biofilm consisting of only blastospores as well as the biofilm consisting of blastospores and filamentous elements (hyphae or/and pseudohyphae). However, the thickness of C. albicans biofilm consisting of blastospores and filamentous elements was much higher than that consisting of only blastospores. The heterogeneity may be regarded as an important feature of the yeast biofilm including C. albicans.

N-trimethylchitosan/alginate layer-by-layer self assembly coatings act as "fungal repellents" to prevent biofilm formation on healthcare materials

Fungal biofilm formation on healthcare materials is a significant clinical concern, often leading to medical-device-related infections, which are difficult to treat. A novel fungal repellent strategy is developed to control fungal biofilm formation. Methylacrylic acid (MAA) is grated onto poly methyl methacrylate (PMMA)-based biomaterials via plasma-initiated grafting polymerization. A cationic polymer, trimethylchitosan (TMC), is synthesized by reacting chitosan with methyl iodide. Sodium alginate (SA) is used as an anionic polymer. TMC/SA multilayers are coated onto the MAA-grafted PMMA via layer-by-layer self-assembly. The TMC/SA multilayer coatings significantly reduce fungal initial adhesion, and effectively prevent fungal biofilm formation. It is concluded that the anti-adhesive property of the surface is due to its hydrophilicity, and that the biofilm-inhibiting action is attributed to the antifungal activity of TMC as well as the chelating function of TMC and SA, which may have acted as fungal repellents. Phosphate buffered saline (PBS)-immersion tests show that the biofilm-modulating effect of the multilayer coatings is stable for more than 4 weeks. Furthermore, the presence of TMC/SA multilayer coatings improves the biocompatibility of the original PMMA, offering a simple, yet effective, strategy for controlling fungal biofilm formation.

Sustained release of a novel anti-quorum-sensing agent against oral fungal biofilms

Thiazolidinedione-8 (S-8) has recently been identified as a potential anti-quorum-sensing/antibiofilm agent against bacteria and fungi. Based on these results, we investigated the possibility of incorporating S-8 in a sustained-release membrane (SRM) to increase its pharmaceutical potential against Candida albicans biofilm. We demonstrated that SRM containing S-8 inhibits fungal biofilm formation in a time-dependent manner for 72 h, due to prolonged release of S-8. Moreover, the SRM effectively delivered the agent in its active form to locations outside the membrane reservoir. In addition, eradication of mature biofilm by the SRM containing S-8 was also significant. Of note, S-8-containing SRM affected the characteristics of mature C. albicans biofilm, such as thickness, exopolysaccharide (EPS) production, and morphogenesis of fungal cells. The concept of using an antibiofilm agent with no antifungal activity incorporated into a sustained-release delivery system is new in medicine and dentistry. This concept of an SRM containing a quorum-sensing quencher with an antibiofilm effect could pave the way for combating oral fungal infectious diseases.

Inhibition of nucleic acid biosynthesis makes little difference to formation of amphotericin B-tolerant persisters in Candida albicans biofilm

Candida albicans persisters constitute a small subpopulation of biofilm cells and play a major role in recalcitrant chronic candidiasis; however, the mechanism underlying persister formation remains unclear. Persisters are often described as dormant, multidrug-tolerant, nongrowing cells. Persister cells are difficult to isolate and study not only due to their low levels in C. albicans biofilms but also due to their transient, reversible phenotype. In this study, we tried to induce persister formation by inducing C. albicans cells into a dormant state. C. albicans cells were pretreated with 5-fluorocytosine (planktonic cells, 0.8 μg ml(-1); biofilm cells, 1 μg ml(-1)) for 6 h at 37°C, which inhibits nucleic acid and protein synthesis. Biofilms and planktonic cultures of eight C. albicans strains were surveyed for persisters after amphotericin B treatment (100 μg ml(-1) for 24 h) and CFU assay. None of the planktonic cultures, with or without 5-fluorocytosine pretreatment, contained persisters. Persister cells were found in biofilms of all tested C. albicans strains, representing approximately 0.01 to 1.93% of the total population. However, the persister levels were not significantly increased in C. albicans biofilms pretreated with 5-fluorocytosine. These results suggest that inhibition of nucleic acid synthesis did not seem to increase the formation of amphotericin B-tolerant persisters in C. albicans biofilms.

Growth inhibition of Candida species by Wickerhamomyces anomalus mycocin and a lactone compound of Aureobasidium pullulans

Background

The increasing resistance of Candida yeasts towards antifungal compounds and the limited choice of therapeutic drugs have spurred great interest amongst the scientific community to search for alternative anti-Candida compounds. Mycocins and fungal metabolites have been reported to have the potential for treatment of fungal infections. In this study, the growth inhibition of Candida species by a mycocin produced by Wickerhamomyces anomalus and a lactone compound from Aureobasidium pullulans were investigated.

Methods

Mycocin was purified from the culture supernatant of an environmental isolate of W. anomalus using Sephadex G-75 gel filtration column chromatography. The mycocin preparation was subjected to SDS-PAGE analysis followed by MALDI TOF/TOF mass spectrometry analysis. The thermal and temperature stability of the mycocin were determined. The glucanase activity of the mycocin was investigated by substrate staining of the mycocin with 4-methyl-umbelliferyl-ß-D-glucoside (MUG). Gas chromatography mass spectrometry (GCMS) analysis was used to identify anti-Candida metabolite in the culture supernatant of an environmental isolate of Aureobasidium pullulans. The inhibitory effects of the anti-Candida compound against planktonic and biofilm cultures of various Candida species were determined using broth microdilution and biofilm quantitation methods.

Results

A mycocin active against Candida mesorugosa but not C. albicans, C. parapsilosis and C. krusei was isolated from the culture supernatant of W. anomalus in this study. The mycocin, identified as exo-ß-1,3 glucanase by MALDI TOF/TOF mass spectrometry, was stable at pH 3–6 and temperature ranging from 4-37°C. The glucanase activity of the mycocin was confirmed by substrate staining with MUG. 5-hydroxy-2-decenoic acid lactone (HDCL) was identified from the culture supernatant of A. pullulans. Using a commercial source of HDCL, the planktonic and biofilm MICs of HDCL against various Candida species were determined in this study.

Conclusions

W. anomalus mycocin demonstrated a narrow spectrum of activity targeting only against C. mesorugosa, while HDCL demonstrated a broad spectrum of inhibitory action against multiple Candida species. The growth inhibition of W. anomalus mycocin and the lactone compound from A. pullulans against Candida yeasts should be further explored for therapeutic potentials against candidiasis.