In vivo Candida glabrata biofilm development on foreign bodies in a rat subcutaneous model

Biofilm Formation in Medically Important Candida Species

Worldwide, the number of infections caused by biofilm-forming fungal pathogens is very high. In human medicine, there is an increasing proportion of immunocompromised patients with prolonged hospitalization, and patients with long-term inserted drains, cannulas, catheters, tubes, or other artificial devices, that exhibit a predisposition for colonization by biofilm-forming yeasts. A high percentage of mortality is due to candidemia caused by medically important Candida species. Species of major clinical significance include C. albicans, C. glabrata, C. tropicalis, C. parapsilosis, C. krusei, and C. auris. The association of these pathogenic species in the biofilm structure is a serious therapeutic problem. Candida cells growing in the form of a biofilm are able to resist persistent therapy thanks to a combination of their protective mechanisms and their ability to disseminate to other parts of the body, thus representing a threat from the perspective of a permanent source of infection. The elucidation of the key mechanisms of biofilm formation is essential to progress in the understanding and treatment of invasive Candida infections.

A Novel Robust Method Mimicking Human Substratum To Dissect the Heterogeneity of Candida auris Biofilm Formation

Candida auris is a pathogen of urgent threat level as marked by the CDC. The formation of biofilms is an essential property of this fungus to establish infection and escape drug treatment. However, our understanding of pathogenesis through biofilm is hampered by heterogeneity in C. auris biofilms observed in different studies. It is imperative to replicate in vivo conditions for studying C. auris biofilm formation in vitro. Different methods are standardized, but the surface used to form biofilms lacks consistency as well as the architecture of a typical biofilm. Here, we report an in vitro technique to grow C. auris biofilms on gelatin-coated coverslips. Interestingly, C. auris cells grown on gelatin-coated coverslips either on modified synthetic sweat media or RPMI 1640 resulted in similar multilayer biofilm formation with extracellular polymeric substances (EPS). This method is also consistent with the biofilm formation of other Candida species, such as Candida glabrata and Candida albicans. Biofilms of C. glabrata developed through this method show pseudohyphae and EPS. This method can be used to understand the molecular basis of biofilm formation, associated pathogenesis, and drug tolerance. The technique is cost-effective and would thus serve in rightful screening and repurposing drug libraries for designing new therapeutics against the less-studied high-alarm pathogen C. auris. IMPORTANCE Heterogeneity is seen when multidrug-resistant C. auris biofilm is cultured using different reported methods. Biofilm formed on the gelatin surface mimics the condition of a host environment that has multilayers and EPS. This method has feasibility for drug screening and analyzing biofilms through three-dimensional (3D) reconstruction. This in vitro biofilm formation technique is also exploited to study the formation of biofilm of other Candida species. The biofilms of C. glabrata and C. albicans can also be correctly mimicked using gelatin in the biofilm-forming environment. Thus, the novel in vitro method for biofilm formation reported here can be widely used to understand the mechanism of biofilm formation, related virulence properties, and drug tolerance of C. auris and other Candida species. This simple and low-cost technique is highly suitable for screening novel inhibitors and repurposed libraries and to design new therapeutics against Candida species.

Νanomaterial-Loaded Polymer Coating Prevents the In Vitro Growth of Candida albicans Biofilms on Silicone Biomaterials

Early failure of silicone voice prostheses resulting from fungal colonization and biofilm formation poses a major concern in modern ear nose throat surgery. Therefore, developing new infection prevention techniques to prolong those implants' survivorship is crucial. We designed an in vitro laboratory study to include nanomaterial-enhanced polymer coating with a plasma spraying technique against Candida albicans growth to address this issue. The anti-biofilm effects of high- and low-dose Al₂O₃ nanowire and TiO₂ nanoparticle coatings were studied either alone or in conjunction with each other using checkerboard testing. It was demonstrated that both nanomaterials were capable of preventing fungal biofilm formation regardless of the anti-fungal agent concentration (median absorbance for high-dose Al₂O₃-enhanced polymer coating was 0.176 [IQR = 0.207] versus control absorbance of 0.805 [IQR = 0.381], p = 0.003 [98% biofilm reduction]; median absorbance for high-dose TiO₂-enhanced polymer coating was 0.186 [IQR = 0.024] versus control absorbance of 0.766 [IQR = 0.458], p < 0.001 [93% biofilm reduction]). Furthermore, synergy was revealed when the Bliss model was applied. According to the findings of this work, it seems that simultaneous consideration of Al₂O₃ and TiO₂ could further increase the existing antibiofilm potential of these nanomaterials and decrease the likelihood of localized toxicity.

Aqueous spice extracts as alternative antimycotics to control highly drug resistant extensive biofilm forming clinical isolates of Candida albicans

Candida albicans form biofilm by associating with biotic and abiotic surfaces. Biofilm formation by C. albicans is relevant and significant as the organisms residing within, gain resistance to conventional antimycotics and are therefore difficult to treat. This study targeted the potential of spice-based antimycotics to control C. albicans biofilms. Ten clinical isolates of C. albicans along with a standard culture MTCC-3017 (ATCC-90028) were screened for their biofilm-forming ability. C. albicans M-207 and C. albicans S-470 were identified as high biofilm formers by point inoculation on Trypticase Soy Agar (TSA) medium as they formed a lawn within 16 h and exhibited resistance to fluconazole and caspofungin at 25 mcg and 8 mcg respectively. Aqueous and organic spice extracts were screened for their antimycotic activity against C. albicans M-207 and S-470 by agar and disc diffusion and a Zone of Inhibition was observed. Minimal Inhibitory Concentration was determined based on growth absorbance and cell viability measurements. The whole aqueous extract of garlic inhibited biofilms of C. albicans M-207, whereas whole aqueous extracts of garlic, clove, and Indian gooseberry were effective in controlling C. albicans S-470 biofilm within 12 h of incubation. The presence of allicin, ellagic acid, and gallic acid as dominant compounds in the aqueous extracts of garlic, clove, and Indian gooseberry respectively was determined by High-Performance Thin Layer Chromatography and Liquid Chromatography-Mass Spectrometry. The morphology of C. albicans biofilm at different growth periods was also determined through bright field microscopy, phase contrast microscopy, and fluorescence microscopy. The results of this study indicated that the alternate approach in controlling high biofilm-forming, multi-drug resistant clinical isolates of C. albicans M-207 and S-470 using whole aqueous extracts of garlic, clove, and Indian gooseberry is a safe, potential, and cost-effective one that can benefit the health care needs with additional effective therapeutics to treat biofilm infections.

Oral Candidiasis of Tobacco Smokers: A Literature Review

The mouth is a vital point of entry into the human body, the health of the mouth entails mental, physical as well as social well-being. Studying diseases, microbiota and environmental conditions of the mouth is important to maintain oral health and all body. The smoke of tobacco cigarettes is one of the worst habits that affect the health of the mouth and the body. Therefore, this review has been conducted to study the effect of smoking on the balance of the oral microbiota and the opportunistic organisms, one of the most important of them &lt;i&gt;Candida&lt;/i&gt;. Although a few studies have found that cigarette smoking does not influence carriage by &lt;i&gt;Candida&lt;/i&gt; significantly. However, most of the studies had results completely contrary to that, smoking cigarettes affect &lt;i&gt;Candida&lt;/i&gt; pathogenic characteristics such as a transition from yeast to hyphal form, biofilm formation and, virulence-related gene expressions. Tobacco is not only an inducer of the transition process but it considers an excellent medium for this process. Furthermore, smoking was significantly associated with &lt;i&gt;Candida&lt;/i&gt; pathogenicity in patients with clinically suspected oral leukoplakia and smoking worsens oral candidiasis and dampens epithelial cell defense response. Nicotine significantly altered the composition and proportion of yeast cells, as well as the extracellular polysaccharide amounts which increase biofilm matrix and thickness which could promote oral candidiasis. Smoking has the potential to alter the oral condition and cause severe oxidative stress, thereby damaging the epithelial barrier of the mouth. These oxidative molecules during smoking activate epithelial cells proteins called oxidative stress-sensing proteins. If some of these proteins induced, widely thought to have anti-inflammatory properties, inhibit the secretion of pro-inflammatory cytokines and are linked to inflammation and oxidative stress is thought to be a possible therapeutic objective and a crucial regulator for smoking-related oral diseases and mouth candidiasis for instance leukoplakia. Also, it is transported into the cell nucleus in the existence of additional electrophilic chemicals to activate antioxidant enzyme gene expression. Therefore, smoking cigarettes destroys oral health and consequently destroys the health of the whole body.

The Antifungal and Antibiofilm Activities of Caffeine against Candida albicans on Polymethyl Methacrylate Denture Base Material

Background: In this study, the effect of pure caffeine was established against Candida albicans (C. albicans) using different microbiological techniques. Methods: Broth microdilution and colony forming units (CFUs) assays were used to detect the minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC). The Live/Dead fluorescent dyes were implemented to determine the yeast viability. Polymethyl methacrylate acrylic resin (PMMA) discs were prepared to evaluate caffeine’s effects against adherent C. albicans using microplate reader, CFUs, and scanning electron microscope (SEM). Results: caffeine’s MIC was detected around 30 mg/mL, while the MFC was considered at 60 mg/mL. In an agar-well diffusion test, the inhibition zones were wider in caffeine groups. The Live/Dead viability test verified caffeine’s antifungal effects. The optical density of the adherent C. albicans on PMMA discs were lower at 620 nm or 410 nm in caffeine groups. CFU count was also reduced by caffeine treatments. SEM revealed the lower adherent C. albicans count in caffeine groups. The effect of caffeine was dose-dependent at which the 60 mg/mL dose demonstrated the most prominent effect. Conclusion: The study reinforced caffeine’s antifungal and antibiofilm properties and suggested it as an additive, or even an alternative, disinfectant solution for fungal biofilms on denture surfaces.

In Vivo Antibacterial Efficacy of Antimicrobial Peptides Modified Metallic Implants─Systematic Review and Meta-Analysis

Biomaterial-associated infection is difficult to detect and brings consequences that can lead to morbidity and mortality. Bacteria can adhere to the implant surface, grow, and form biofilms. Antimicrobial peptides (AMPs) can target and kill bacterial cells using a plethora of mechanisms of action such as rupturing the cell membrane by creating pores via depolarization with their cationic and amphipathic nature. AMPs can thus be coated onto metal implants to prevent microbial cell adhesion and growth. The aim of this systematic review was to determine the potential clinical applications of AMP-modified implants through in vivo induced infection models. Following a database search recently up to 22 January 2022 using PubMed, Web of Science and Cochrane databases, and abstract/title screening using the PRISMA framework, 24 studies remained, of which 18 were used in the random effects meta-analysis of standardized mean differences (SMD) to get effect sizes. Quality of studies was assessed using SYRCLE's risk of bias tool. The data from these 18 studies showed that AMPs carry antibacterial effects, and the meta-analysis confirmed the favorited antibacterial efficacy of AMP-coated groups over controls (SMD -1.74, 95%CI [-2.26, -1.26], p < 0.00001). Subgroup analysis showed that the differences in effect size are random, and high heterogeneity values suggested the same. HHC36 and vancomycin were the most common AMPs for surface modification and Staphylococcus aureus, the most tested bacterium in vivo. Covalent binding with polymer brush coating and physical layer-by-layer incorporation of AMPs were recognized as key methods of incorporation to achieve desired densities. The use of fusion peptides seemed admirable to incorporate additional benefits such as osteointegration and wound healing and possibly targeting more microbe strains. Further investigation into the incorporation methods, AMP activity against different bacterial strains, and the number of AMPs used for metal implant surface modification is needed to progress toward potential clinical application.

Niacin Limitation Promotes Candida glabrata Adhesion to Abiotic Surfaces

Candida glabrata is a prevalent fungal pathogen in humans, which is able to adhere to host cells and abiotic surfaces. Nicotinic acid (NA) limitation has been shown to promote the adherence of C. glabrata to human epithelial cells. Clinically, the elderly and hospitalized patients who are prone to C. glabrata–related denture stomatitis often suffer from vitamin deficiency. This study aimed to investigate C. glabrata adhesion to abiotic surfaces, including acrylic resin (a denture material) surfaces, cell surface hydrophobicity and adhesion gene expression. C. glabrata CBS138 was grown in media containing decreasing NA concentrations (40, 0.4, 0.04 and 0.004 µM). Adherence of C. glabrata to glass coverslips and acrylic resin was analyzed. C. glabrata adhesion to both surfaces generally increased with decreasing NA concentrations. The highest adhesion was found for the cells grown with 0.004 µM NA. The cell surface hydrophobicity test indicated that NA limitation enhanced hydrophobicity of C. glabrata cells. Quantitative PCR showed that of all adhesion genes tested, EPA1, EPA3 and EPA7 were significantly up-regulated in both 0.004 µM NA and 0.04 µM NA groups compared to those in the 40 µM NA group. No significant up- or down-regulation under NA limitation was observed for the other tested adhesion genes, namely AWP3, AWP4, AWP6 and EPA6. NA limitation resulted in increased expression of some adhesion genes, higher surface hydrophobicity of C. glabrata and enhanced adhesion to abiotic surfaces. NA deficiency is likely a risk factor for C. glabrata–related denture stomatitis in the elderly.

A Complex Microbial Interplay Underlies Recurrent Vulvovaginal Candidiasis Pathobiology

While extremely prevalent, painful, and difficult to treat, vulvovaginal candidiasis remains largely understudied in the field of women's health. In a recent issue of mSystems, McKloud et al. (E. McKloud, C. Delaney, L. Sherry, R. Kean, et al., mSystems 6:e00622-21, 2021, https://doi.org/10.1128/mSystems.00622-21) shed light on a pivotal role of a complex Candida-Lactobacillus interplay that may regulate the pathophysiology of recurrent vulvovaginal candidiasis (RVVC). This advancement not only gives new insight into the molecular mechanisms governing interkingdom interactions modulating RVVC disease, but also provides evidence that probiotic Lactobacillus-based therapeutic approaches could be efficient for fighting these problematical fungal infections.

From the first touch to biofilm establishment by the human pathogen Candida glabrata: a genome-wide to nanoscale view

Candida glabrata is an opportunistic pathogen that adheres to human epithelial mucosa and forms biofilm to cause persistent infections. In this work, Single-cell Force Spectroscopy (SCFS) was used to glimpse at the adhesive properties of C. glabrata as it interacts with clinically relevant surfaces, the first step towards biofilm formation. Following a genetic screening, RNA-sequencing revealed that half of the entire transcriptome of C. glabrata is remodeled upon biofilm formation, around 40% of which under the control of the transcription factors CgEfg1 and CgTec1. Using SCFS, it was possible to observe that CgEfg1, but not CgTec1, is necessary for the initial interaction of C. glabrata cells with both abiotic surfaces and epithelial cells, while both transcription factors orchestrate biofilm maturation. Overall, this study characterizes the network of transcription factors controlling massive transcriptional remodelling occurring from the initial cell-surface interaction to mature biofilm formation.

The isolation and identification of Candida glabrata from avian species and a study of the antibacterial activities of Chinese herbal medicine in vitro

Previously, a fungus was isolated from a diseased pigeon group clinically suspected of being infected with Candida. The fungus was subsequently identified as Candida glabrata using morphology, physiology, biochemistry, and molecular biology testing methods. In the present study, to determine the controlling effects of Chinese herbal medicine for C. glabrata, the bacteriostatic effects of the ethanol extracts Acorus gramineus, Sophora flavescens, Polygonum hydropiper, Cassia obtusifolia, Pulsatilla chinensis, Dandelion, and Cortex phellodendri on C. glabrata in vitro were analyzed. The results showed that the minimum inhibitory concentrations (MIC₈₀) of Cortex phellodendri was 0.25 μg/μL. Meanwhile, that of S. flavescens was 32 μg/μL; C. obtusifolia was 56 μg/μL; A. gramineus and Polygonum hydropiper was 64 μg/μL; and P. chinensis was 112 μg/μL. However, MIC₈₀ for Dandelion was undetectable. In addition, improved drug sensitivity tests revealed that colonies had grown after 24 h in the blank group, as well as the Polygonum hydropiper, P. chinensis, Dandelion, and ethanol groups. The colonies first appeared at the 48-hour point in the other drug-sensitive medium of Chinese herbal medicine. However, no colony growth was found in Cortex phellodendri medium, and the formation of the maximum colony diameter in that group was later than the blank group (e.g., 96 h in the blank group and 120 h in the Chinese herbal medicine group). It was observed that only 17 colony-forming units had grown in 125 μg/μL of the S. flavescens medium, which was significantly different from other groups. Also, the final colony diameter was significantly smaller than that of the other experimental groups. Therefore, it was determined that the A. gramineus, S. flavescens, Polygonum hydropiper, Cassia obtusifolia, P. chinensis, and Cortex phellodendri had certain inhibitory effects on the growth of the C. glabrata. Among those, it was observed that the Cortex phellodendri had the strongest inhibitory effects, followed by the S. flavescens. In the future, these Chinese herbal medicines are expected to be used to treat the fungal infections related to C. glabrata in poultry to improve production performance.

Host-pathogen interaction in Candida glabrata infection: current knowledge and implications for antifungal therapy

INTRODUCTION

The opportunistic fungal pathogen Candida glabrata poses a clinical challenge in the successful treatment of invasive Candida infections, owing to its low inherent susceptibility toward azole antifungals and the recent acquisition of coresistance toward azole and echinocandin drugs. Compared to other prevalent Candida bloodstream pathogens, C. glabrata neither exhibits secreted proteolytic activity nor invokes a strong immune response in a variety of host cells and is less virulent. It also does not form true hyphae, and the success of C. glabrata, therefore, as a prevalent human fungal pathogen, appears to be built upon a distinct set of virulence attributes.

AREAS COVERED

The focus of this review is to outline, in brief, the interaction of C. glabrata with the host, deduced from the knowledge gained from different in vitro, ex vivo, and in vivo model systems. In addition, we briefly discuss the current antifungals, antifungal resistance mechanisms, and the development of new antifungal therapies, along with the available information on the host response.

EXPERT OPINION

A detailed understanding of stresses, selection pressures and differential immune responses in the presence and absence of antifungals that C. glabrata encounters in varied niches of the host, is required to design effective antifungal therapy.

How Biofilm Growth Affects Candida-Host Interactions

Candida spp. proliferate as surface-associated biofilms in a variety of clinical niches. These biofilms can be extremely difficult to eradicate in healthcare settings. Cells within biofilm communities grow as aggregates and produce a protective extracellular matrix, properties that impact the ability of the host to respond to infection. Cells that disperse from biofilms display a phenotype of enhanced pathogenicity. In this review, we highlight host-biofilm interactions for Candida, focusing on how biofilm formation influences innate immune responses.

Garlic alters the expression of putative virulence factor genes SIR2 and ECE1 in vulvovaginal C. albicans isolates

Vulvovaginal candidiasis causes sufferers much discomfort. Phytotherapy with garlic has been reported to be a possible alternative form of treatment; however, it is unknown why patients report varying success with this strategy. Fresh garlic extract has been shown to down-regulate the putative virulence gene, SIR2 in C. albicans. Our study aimed to see if previous observations were reproducible for the gene responsible for Candidalysin (ECE1). Two clinical strains from patients with reported variable efficacy of using garlic for the treatment of vulvovaginal candidiasis were compared through biofilm assays and antimicrobial susceptibility. Real-time PCR was used to assess changes in gene expression when exposed to garlic. Treatment with fresh garlic extract and pure allicin (an active compound produced in cut garlic) resulted in a decrease in SIR2 expression in all strains. In contrast, ECE1 expression was up-regulated in a reference strain and an isolate from a patient unresponsive to garlic therapy, while in an isolate from a patient responsive to garlic therapy, down-regulation of ECE1 occurred. Future studies that investigate the effectiveness of phytotherapies should take into account possible varying responses of individual strains and that gene expression may be amplified in the presence of serum.

Screening the Drug:H+ Antiporter Family for a Role in Biofilm Formation in Candida glabrata

Biofilm formation and drug resistance are two key pathogenesis traits exhibited by Candida glabrata as a human pathogen. Interestingly, specific pathways appear to be in the crossroad between the two phenomena, making them promising targets for drug development. In this study, the 10 multidrug resistance transporters of the Drug:H⁺ Antiporter family of C. glabrata were screened for a role in biofilm formation. Besides previously identified players in this process, namely CgTpo1_2 and CgQdr2, two others are shown to contribute to biofilm formation: CgDtr1 and CgTpo4. The deletion of each of these genes was found to lead to lower biofilm formation, in both SDB and RPMI media, while their expression was found to increase during biofilm development and to be controlled by the transcription factor CgTec1, a predicted key regulator of biofilm formation. Additionally, the deletion of CgDTR1, CgTPO4, or even CgQDR2 was found to increase plasma membrane potential and lead to decreased expression of adhesin encoding genes, particularly CgALS1 and CgEPA1, during biofilm formation. Although the exact role of these drug transporters in biofilm formation remains elusive, our current model suggests that their control over membrane potential by the transport of charged molecules, may affect the perception of nutrient availability, which in turn may delay the triggering of adhesion and biofilm formation.

Transcriptional responses of Candida glabrata biofilm cells to fluconazole are modulated by the carbon source

Candida glabrata is an important human fungal pathogen known to trigger serious infections in immune-compromised individuals. Its ability to form biofilms, which exhibit high tolerance to antifungal treatments, has been considered as an important virulence factor. However, the mechanisms involving antifungal resistance in biofilms and the impact of host niche environments on these processes are still poorly defined. In this study, we performed a whole-transcriptome analysis of C. glabrata biofilm cells exposed to different environmental conditions and constraints in order to identify the molecular pathways involved in fluconazole resistance and understand how acidic pH niches, associated with the presence of acetic acid, are able to modulate these responses. We show that fluconazole treatment induces gene expression reprogramming in a carbon source and pH-dependent manner. This is particularly relevant for a set of genes involved in DNA replication, ergosterol, and ubiquinone biosynthesis. We also provide additional evidence that the loss of mitochondrial function is associated with fluconazole resistance, independently of the growth condition. Lastly, we propose that C. glabrata Mge1, a cochaperone involved in iron metabolism and protein import into the mitochondria, is a key regulator of fluconazole susceptibility during carbon and pH adaptation by reducing the metabolic flux towards toxic sterol formation. These new findings suggest that different host microenvironments influence directly the physiology of C. glabrata, with implications on how this pathogen responds to antifungal treatment. Our analyses identify several pathways that can be targeted and will potentially prove to be useful for developing new antifungals to treat biofilm-based infections.

Bioactive Peptides Against Fungal Biofilms

Infections caused by invasive fungal biofilms have been widely associated with high morbidity and mortality rates, mainly due to the advent of antibiotic resistance. Moreover, fungal biofilms impose an additional challenge, leading to multidrug resistance. This fact, along with the contamination of medical devices and the limited number of effective antifungal agents available on the market, demonstrates the importance of finding novel drug candidates targeting pathogenic fungal cells and biofilms. In this context, an alternative strategy is the use of antifungal peptides (AFPs) against fungal biofilms. AFPs are considered a group of bioactive molecules with broad-spectrum activities and multiple mechanisms of action that have been widely used as template molecules for drug design strategies aiming at greater specificity and biological efficacy. Among the AFP classes most studied in the context of fungal biofilms, defensins, cathelicidins and histatins have been described. AFPs can also act by preventing the formation of fungal biofilms and eradicating preformed biofilms through mechanisms associated with cell wall perturbation, inhibition of planktonic fungal cells’ adhesion onto surfaces, gene regulation and generation of reactive oxygen species (ROS). Thus, considering the critical scenario imposed by fungal biofilms and associated infections and the application of AFPs as a possible treatment, this review will focus on the most effective AFPs described to date, with a core focus on antibiofilm peptides, as well as their efficacy in vivo, application on surfaces and proposed mechanisms of action.

Nicotine enhances the thickness of biofilm and adherence of Candida albicans ATCC 14053 and Candida parapsilosis ATCC 22019

Candida albicans ATCC 14053 and Candida parapsilosis ATCC 22019 hyphal-wall protein 1 (HWP1) are involved in hyphae formation and pathogenesis. The transcriptional agglutinin-like sequence 3 (ALS3) genes in both species are responsible for the development of biofilm and colonization on tooth surfaces. Therefore, we investigated the expression of HWP1 and ALS3 quantitatively in C. albicans and C. parapsilosis and examined the biofilm structure upon exposure to various nicotine concentrations. In vitro, biofilms of Candida species were developed directly on slides using the Lab-Tek Chamber Slide System and visualized by confocal laser scanning microscopy. Quantitative real-time polymerase chain reaction was used to measure HWP1 and ALS3 expression in C. albicans ATCC 14053 and C. parapsilosis ATCC 22019. The results indicated that nicotine multiplied the number of yeast cells and increased the extracellular polysaccharides of Candida species. We also found that 1-2 mg/mL nicotine could enhance the formation of biofilm. The findings also revealed that the expression of HWP1 and ALS3 in Candida species were increased as the nicotine concentration increased. Therefore, nicotine influences the biofilm development of oral-associated C. albicans ATCC 14053 and C. parapsilosis ATCC 22019.

Divergent Approaches to Virulence in C. albicans and C. glabrata: Two Sides of the Same Coin

Candida albicans and Candida glabrata are the two most prevalent etiologic agents of candidiasis worldwide. Although both are recognized as pathogenic, their choice of virulence traits is highly divergent. Indeed, it appears that these different approaches to fungal virulence may be equally successful in causing human candidiasis. In this review, the virulence mechanisms employed by C. albicans and C. glabrata are analyzed, with emphasis on the differences between the two systems. Pathogenesis features considered in this paper include dimorphic growth, secreted enzymes and signaling molecules, and stress resistance mechanisms. The consequences of these traits in tissue invasion, biofilm formation, immune system evasion, and macrophage escape, in a species dependent manner, are discussed. This review highlights the observation that C. albicans and C. glabrata follow different paths leading to a similar outcome. It also highlights the lack of knowledge on some of the specific mechanisms underlying C. glabrata pathogenesis, which deserve future scrutiny.

Candida glabrata: A Lot More Than Meets the Eye

Candida glabrata is an opportunistic human fungal pathogen that causes superficial mucosal and life-threatening bloodstream infections in individuals with a compromised immune system. Evolutionarily, it is closer to the non-pathogenic yeast Saccharomyces cerevisiae than to the most prevalent Candida bloodstream pathogen, C. albicans. C. glabrata is a haploid budding yeast that predominantly reproduces clonally. In this review, we summarize interactions of C. glabrata with the host immune, epithelial and endothelial cells, and the ingenious strategies it deploys to acquire iron and phosphate from the external environment. We outline various attributes including cell surface-associated adhesins and aspartyl proteases, biofilm formation and stress response mechanisms, that contribute to the virulence of C. glabrata. We further discuss how, C. glabrata, despite lacking morphological switching and secreted proteolytic activity, is able to disarm macrophage, dampen the host inflammatory immune response and replicate intracellularly.

Monitoring of Fluconazole and Caspofungin Activity against In Vivo Candida glabrata Biofilms by Bioluminescence Imaging

Candida glabrata can attach to various medical implants and forms thick biofilms despite its inability to switch from yeast to hyphae. The current in vivo C. glabrata biofilm models only provide limited information about colonization and infection and usually require animal sacrifice. To gain real-time information from individual BALB/c mice, we developed a noninvasive imaging technique to visualize C. glabrata biofilms in catheter fragments that were subcutaneously implanted on the back of mice. Bioluminescent C. glabrata reporter strains (luc _OPT 7/2/4 and luc _OPT 8/1/4), free of auxotrophic markers, expressing a codon-optimized firefly luciferase were generated. A murine subcutaneous model was used to follow real-time in vivo biofilm formation in the presence and absence of fluconazole and caspofungin. The fungal load in biofilms was quantified by CFU counts and by bioluminescence imaging (BLI). C. glabrata biofilms formed within the first 24 h, as documented by the increased number of device-associated cells and elevated bioluminescent signal compared with adhesion at the time of implant. The in vivo model allowed monitoring of the antibiofilm activity of caspofungin against C. glabrata biofilms through bioluminescent imaging from day four after the initiation of treatment. Contrarily, signals emitted from biofilms implanted in fluconazole-treated mice were similar to the light emitted from control-treated mice. This study gives insights into the real-time development of C. glabrata biofilms under in vivo conditions. BLI proved to be a dynamic, noninvasive, and sensitive tool to monitor continuous biofilm formation and activity of antifungal agents against C. glabrata biofilms formed on abiotic surfaces in vivo.

Biofilms and vulvovaginal candidiasis

Candida species, including C. albicans, are part of the mucosal flora of most healthy women, and inhabit the gastrointestinal and genitourinary tracts. Under favourable conditions, they can colonize the vulvovaginal mucosa, giving rise to symptomatic vulvovaginal candidiasis (VVC). The mechanism by which Candida spp. produces inflammation is unknown. Both, the blastoconidia and the pseudohyphae are capable of destroying the vaginal epithelium by direct invasion. Although the symptoms are not always related to the fungal burden, in general, VVC is associated with a greater number of yeasts and pseudohyphae. Some years ago, C. albicans was the species most frequently involved in the different forms of VVC. However, infections by different species have emerged during the last two decades producing an increase in causative species of VVC such as C. glabrata, C. parapsilosis, C. krusei and C. tropicalis. Candida species are pathogenic organisms that have two forms of development: planktonic and biofilm. A biofilm is defined as a community of microorganisms attached to a surface and encompassed by an extracellular matrix. This form of presentation gives microorganisms greater resistance to antifungal agents. This review, about Candia spp. with a special emphasis on Candida albicans discusses specific areas such as biofilm structure and development, cell morphology and biofilm formation, biofilm-associated gene expression, the cell surface and adherence, the extracellular matrix, biofilm metabolism, and biofilm drug resistance in vulvovaginitis biofilms as an important virulence factor in fungi.

Antagonistic Interaction of Staphylococcus aureus Toward Candida glabrata During in vitro Biofilm Formation Is Caused by an Apoptotic Mechanism

Background: Infections caused by Candida species and Staphylococcus aureus are associated with biofilm formation. C. albicans–S. aureus interactions are synergistic due to the significant increase in mixed biofilms and improved resistance to vancomycin of S. aureus. C. glabrata and S. aureus both are nosocomial pathogens that cause opportunistic infections in similar host niches. However, there is scarce information concerning the interaction between these last microorganisms.

Results: The relationship between C. glabrata and S. aureus was evaluated by estimating the viability of both microorganisms in co-culture of planktonic cells and in single and mixed biofilms. An antagonistic behavior of S. aureus and their cell-free bacterial supernatant (CFBS) toward C. glabrata, both in planktonic form and in biofilms, was demonstrated. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and confocal laser scanning microscopy (CLSM) images showed yeast cells surrounded by bacteria, alterations in intracytoplasmic membranes, and non-viable blastoconidia with intact cell walls. Concomitantly, S. aureus cells remained viable and unaltered. The antagonistic activity of S. aureus toward C. glabrata was not due to cell-to-cell contact but the presence of CFBS, which causes a significant decrement in yeast viability and the formation of numerous lipid droplets (LDs), reactive oxygen species (ROS) accumulation, as well as nuclear alterations, and DNA fragmentation indicating the induction of an apoptotic mechanism.

Conclusion: Our results demonstrate that the S. aureus CFBS causes cell death in C. glabrata by an apoptotic mechanism.

Methodologies for in vitro and in vivo evaluation of efficacy of antifungal and antibiofilm agents and surface coatings against fungal biofilms

Unlike superficial fungal infections of the skin and nails, which are the most common fungal diseases in humans, invasive fungal infections carry high morbidity and mortality, particularly those associated with biofilm formation on indwelling medical devices. Therapeutic management of these complex diseases is often complicated by the rise in resistance to the commonly used antifungal agents. Therefore, the availability of accurate susceptibility testing methods for determining antifungal resistance, as well as discovery of novel antifungal and antibiofilm agents, are key priorities in medical mycology research. To direct advancements in this field, here we present an overview of the methods currently available for determining (i) the susceptibility or resistance of fungal isolates or biofilms to antifungal or antibiofilm compounds and compound combinations; (ii) the in vivo efficacy of antifungal and antibiofilm compounds and compound combinations; and (iii) the in vitro and in vivo performance of anti-infective coatings and materials to prevent fungal biofilm-based infections.

Adhesins in Candida glabrata

The human fungal pathogen Candida glabrata is causing more and more problems in hospitals, as this species shows an intrinsic antifungal drug resistance or rapidly becomes resistant when challenged with antifungals. C. glabrata only grows in the yeast form, so it is lacking a yeast-to-hyphae switch, which is one of the main virulence factors of C. albicans. An important virulence factor of C. glabrata is its capacity to strongly adhere to many different substrates. To achieve this, C. glabrata expresses a large number of adhesin-encoding genes and genome comparisons with closely related species, including the non-pathogenic S. cerevisiae, which revealed a correlation between the number of adhesin-encoding genes and pathogenicity. The adhesins are involved in the first steps during an infection; they are the first point of contact with the host. For several of these adhesins, their importance in adherence to different substrates and subsequent biofilm formation was demonstrated in vitro or in vivo. In this review, we provide an overview of the role of C. glabrata adhesins during adhesion and biofilm formation both, under in vitro and in vivo conditions.

Murine model for the evaluation of candiduria caused by Candida tropicalis from biofilm

To evaluate the pathophysiology of catheter-associated candiduria, the bladders of female mice were infected with Candida tropicalis. One group was implanted with a catheter fragment with preformed biofilm by cystotomy technique, while another group received, in separate, a sterile catheter fragment and a correspondent yeast suspension. The bladder tissues were examined by histopathology and the quantity of colony forming units was evaluated. All the animals presented inflammation and the presence of C. tropicalis was observed in the tissue within 72 h of the introduction of biofilm, while 75% of the mice remained infected after 144 h. However, only 50% of animals from the group infected with C. tropicalis in suspension (planktonic yeasts), exhibited such signs of infection over time. The cystotomy technique is therefore viable in mice, and is an effective model for evaluating the pathogenesis of candiduria from catheter biofilms. The model revealed the potential of C. tropicalis infectivity and demonstrated more effective evasion of the host response in biofilm form than the planktonic yeast.

Candida Biofilms: Threats, Challenges, and Promising Strategies

Candida species are fungal pathogens known for their ability to cause superficial and systemic infections in the human host. These pathogens are able to persist inside the host due to the development of pathogenicity and multidrug resistance traits, often leading to the failure of therapeutic strategies. One specific feature of Candida species pathogenicity is their ability to form biofilms, which protects them from external factors such as host immune system defenses and antifungal drugs. This review focuses on the current threats and challenges when dealing with biofilms formed by Candida albicans, Candida glabrata, Candida tropicalis, and Candida parapsilosis, highlighting the differences between the four species. Biofilm characteristics depend on the ability of each species to produce extracellular polymeric substances (EPS) and display dimorphic growth, but also on the biofilm substratum, carbon source availability and other factors. Additionally, the transcriptional control over processes like adhesion, biofilm formation, filamentation, and EPS production displays great complexity and diversity within pathogenic yeasts of the Candida genus. These differences not only have implications in the persistence of colonization and infections but also on antifungal resistance typically found in Candida biofilm cells, potentiated by EPS, that functions as a barrier to drug diffusion, and by the overexpression of drug resistance transporters. The ability to interact with different species in in vivo Candida biofilms is also a key factor to consider when dealing with this problem. Despite many challenges, the most promising strategies that are currently available or under development to limit biofilm formation or to eradicate mature biofilms are discussed.

Fungal Biofilms and Polymicrobial Diseases

Biofilm formation is an important virulence factor for pathogenic fungi. Both yeasts and filamentous fungi can adhere to biotic and abiotic surfaces, developing into highly organized communities that are resistant to antimicrobials and environmental conditions. In recent years, new genera of fungi have been correlated with biofilm formation. However, Candida biofilms remain the most widely studied from the morphological and molecular perspectives. Biofilms formed by yeast and filamentous fungi present differences, and studies of polymicrobial communities have become increasingly important. A key feature of resistance is the extracellular matrix, which covers and protects biofilm cells from the surrounding environment. Furthermore, to achieve cell–cell communication, microorganisms secrete quorum-sensing molecules that control their biological activities and behaviors and play a role in fungal resistance and pathogenicity. Several in vitro techniques have been developed to study fungal biofilms, from colorimetric methods to omics approaches that aim to identify new therapeutic strategies by developing new compounds to combat these microbial communities as well as new diagnostic tools to identify these complex formations in vivo. In this review, recent advances related to pathogenic fungal biofilms are addressed.

Exploiting Interkingdom Interactions for Development of Small-Molecule Inhibitors of Candida albicans Biofilm Formation

A rapid decline in the development of new antimicrobial therapeutics has coincided with the emergence of new and more aggressive multidrug-resistant pathogens. Pathogens are protected from antibiotic activity by their ability to enter an aggregative biofilm state. Therefore, disrupting this process in pathogens is a key strategy for the development of next-generation antimicrobials. Here, we present a suite of compounds, based on the Pseudomonas aeruginosa 2-heptyl-4(1H)-quinolone (HHQ) core quinolone interkingdom signal structure, that exhibit noncytotoxic antibiofilm activity toward the fungal pathogen Candida albicans In addition to providing new insights into what is a clinically important bacterium-fungus interaction, the capacity to modularize the functionality of the quinolone signals is an important advance in harnessing the therapeutic potential of signaling molecules in general. This provides a platform for the development of potent next-generation small-molecule therapeutics targeting clinically relevant fungal pathogens.

Management of Candida biofilms: state of knowledge and new options for prevention and eradication

Biofilms formed by Candida species (spp.) on medical devices represent a potential health risk. The focus of current research is searching for new options for the treatment and prevention of biofilm-associated infections using different approaches including modern nanotechnology. This review summarizes current information concerning the most relevant resistance/tolerance mechanisms to conventional drugs and a role of additional factors contributing to these phenomena in Candida spp. (mostly Candida albicans). Additionally, it provides an information update in prevention and eradication of a Candida biofilm including experiences with 'lock' therapy, potential utilization of small molecules in biomedical applications, and perspectives of using photodynamic inactivation in the control of a Candida biofilm.

Biofilm formation in Candida glabrata: What have we learnt from functional genomics approaches?

Biofilms are a source of therapeutic failures because of their intrinsic tolerance to antimicrobials. Candida glabrata is one of the pathogenic yeasts that is responsible for life-threatening disseminated infections and able to form biofilms on medical devices such as vascular and urinary catheters. Recent progresses in the functional genomics of C. glabrata have been applied to the study of biofilm formation, revealing the contribution of an array of genes to this process. In particular, the Yak1 kinase and the Swi/Snf chromatin remodeling complex have been shown to relieve the repression exerted by subtelomeric silencing on the expression of the EPA6 and EPA7 genes, thus allowing the encoded adhesins to exert their key roles in biofilm formation. This provides a framework to evaluate the contribution of other genes that have been genetically linked to biofilm development and, based on the function of their orthologs in Saccharomyces cerevisiae, appear to have roles in adaptation to nutrient deprivation, calcium signaling, cell wall remodeling and adherence. Future studies combining the use of in vitro and animal models of biofilm formation, omics approaches and forward or reverse genetics are needed to expand the current knowledge of C. glabrata biofilm formation and reveal the mechanisms underlying their antifungal tolerance.

Biofilms: An Underappreciated Mechanism of Treatment Failure and Recurrence in Vaginal Infections

Biofilms are microbial communities of surface-attached cells embedded in a self-produced extracellular matrix. They are of major medical significance because they decrease susceptibility to antimicrobial agents and enhance the spread of antimicrobial resistance. Biofilm-associated bacterial and fungal microorganisms have increasingly been recognized to play a role in multiple infectious diseases, particularly in their persistence and recurrence. More recently, biofilms have also been implicated in vaginal infections, notably bacterial vaginosis (BV) and vulvovaginal candidiasis (VVC), particularly in the setting of treatment failure and recurrence. The purpose of this review is to discuss the impact of biofilms on the management and treatment of BV and recurrent VVC and highlight the need for additional research and development of novel therapeutics targeting pathogenic vaginal biofilms.

Deletion of the DNA Ligase IV Gene in Candida glabrata Significantly Increases Gene-Targeting Efficiency

Candida glabrata is reported as the second most prevalent human opportunistic fungal pathogen in the United States. Over the last decades, its incidence increased, whereas that of Candida albicans decreased slightly. One of the main reasons for this shift is attributed to the inherent tolerance of C. glabrata toward the commonly used azole antifungal drugs. Despite a close phylogenetic distance to Saccharomyces cerevisiae, homologous recombination works with poor efficiency in C. glabrata compared to baker's yeast, in fact limiting targeted genetic alterations of the pathogen's genome. It has been shown that nonhomologous DNA end joining is dominant over specific gene targeting in C. glabrata. To improve the homologous recombination efficiency, we have generated a strain in which the LIG4 gene has been deleted, which resulted in a significant increase in correct gene targeting. The very specific function of Lig4 in mediating nonhomologous end joining is the reason for the absence of clear side effects, some of which affect the ku80 mutant, another mutant with reduced nonhomologous end joining. We also generated a LIG4 reintegration cassette. Our results show that the lig4 mutant strain may be a valuable tool for the C. glabrata research community.