Candida Biofilms: Threats, Challenges, and Promising Strategies

The Anti-candidal and Absorbtion Performance of PVA/PVP-Based Jania rubens Hydrogel on Candida tropicalis and Some Physicochemical Properties of the Hydrogel

This study was aimed to create a bioactive hydrogel form with PVA/PVP (polyvinyl alcohol/poly(N-vinylpyrrolidone) polymer using acetone and ethanol extractions of Jania rubens red algae and investigate some pharmaceutical properties. The anti-candidal activity and some inhibition performance of J. rubens/PVA/PVP hydrogel were investigated on Candida tropicalis which is one of the important causes of bloodstream infections. The physicochemical properties of J. rubens/PVA/PVP hydrogel were revealed using FTIR and swelling-absorption tests. The volatile compounds of J. rubens extracts were examined by GCMS. By mixing the extracts in equal proportions, PVA/PVP-based hydrogel was prepared. According to the results, Cumulative Drug Release was stable at 25 °C for the first 5 h. The IZ (inhibition zone) and MIC (minimum inhibitory concentration) of J. rubens/PVA/PVP hydrogel were 9.01 mm and 80.20 mg/mL, respectively. It was found that logarithmic reduction and percent reduction were seen as 1.5 CFU/mL and 97.5%, respectively, on C. tropicalis exposed to J. rubens/PVA/PVP hydrogel in the first 5 min of the incubation. After exposure of C. tropicalis to J. rubens/PVA/PVP, the number of viable cells transferred from the gel to water was between 76.1 and 73.1% in high glucose medium, while it was between 92.2 and 80.8% for the PVA/PVP hydrogel under the same conditions. As a result, PVA/PVP hydrogel was made bioactive with J. rubens extracts for the first time in this study, and its potential for use as a functional anticandidal hydrogel on C. tropicalis has been demonstrated.

Candida albicans and Candida glabrata: global priority pathogens

SUMMARYA significant increase in the incidence of Candida-mediated infections has been observed in the last decade, mainly due to rising numbers of susceptible individuals. Recently, the World Health Organization published its first fungal pathogen priority list, with Candida species listed in medium, high, and critical priority categories. This review is a synthesis of information and recent advances in our understanding of two of these species-Candida albicans and Candida glabrata. Of these, C. albicans is the most common cause of candidemia around the world and is categorized as a critical priority pathogen. C. glabrata is considered a high-priority pathogen and has become an increasingly important cause of candidemia in recent years. It is now the second most common causative agent of candidemia in many geographical regions. Despite their differences and phylogenetic divergence, they are successful as pathogens and commensals of humans. Both species can cause a broad variety of infections, ranging from superficial to potentially lethal systemic infections. While they share similarities in certain infection strategies, including tissue adhesion and invasion, they differ significantly in key aspects of their biology, interaction with immune cells, host damage strategies, and metabolic adaptations. Here we provide insights on key aspects of their biology, epidemiology, commensal and pathogenic lifestyles, interactions with the immune system, and antifungal resistance.

Roles of alcohol dehydrogenase 1 in the biological activities of Candida albicans

Candida albicans stands as the foremost prevalent human commensal pathogen and a significant contributor to nosocomial fungal infections. In the metabolism of C. albicans, alcohol dehydrogenase 1 (Adh1) is one of the important enzymes that converts acetaldehyde produced by pyruvate decarboxylation into ethanol at the end of glycolysis. Leveraging the foundational processes of alcoholic fermentation, Adh1 plays an active role in multiple biological phenomena, including biofilm formation, interactions between different species, the development of drug resistance, and the potential initiation of gastrointestinal cancer. Additionally, Adh1 within C. albicans has demonstrated associations with regulating the cell cycle, stress responses, and various intracellular states. Furthermore, Adh1 is extracellularly localized on the cell wall surface, where it plays roles in processes such as tissue invasion and host immune responses. Drawing from an analysis of ADH1 gene structure, expression patterns, and fundamental functions, this review elucidates the intricate connections between Adh1 and various biological processes within C. albicans, underscoring its potential implications for the prevention, diagnosis, and treatment of candidiasis.

Spectrum of activity and mechanisms of azole-bisphosphonate synergy in pathogenic Candida

Candidiasis places a significant burden on human health and can range from common superficial vulvovaginal and oral infections to invasive diseases with high mortality. The most common Candida species implicated in human disease is Candida albicans, but other species like Candida glabrata are emerging. The use of azole antifungals for treatment is limited by increasing rates of resistance. This study explores repositioning bisphosphonates, which are traditionally used for osteoporosis, as antifungal synergists that can improve and revitalize the use of azoles. Risedronate, alendronate, and zoledronate (ZOL) were tested against isolates from six different species of Candida, and ZOL produced moderate antifungal activity and strong synergy with azoles like fluconazole (FLC), particularly in C. glabrata. FLC:ZOL combinations had increased fungicidal and antibiofilm activity compared to either drug alone, and the combination prevented the development of antifungal resistance. Mechanistic investigations demonstrated that the synergy was mediated by the depletion of squalene, resulting in the inhibition of ergosterol biosynthesis and a compromised membrane structure. In C. glabrata, synergy compromised the function of membrane-bound multidrug transporters and caused an accumulation of reactive oxygen species, which may account for its acute sensitivity to FLC:ZOL. The efficacy of FLC:ZOL in vivo was confirmed in a Galleria mellonella infection model, where combinations improved the survival of larvae infected with C. albicans and C. glabrata to a greater extent than monotherapy with FLC or ZOL, and at reduced dosages. These findings demonstrate that bisphosphonates and azoles are a promising new combination therapy for the treatment of topical candidiasis.

IMPORTANCE

Candida is a common and often very serious opportunistic fungal pathogen. Invasive candidiasis is a prevalent cause of nosocomial infections with a high mortality rate, and mucocutaneous infections significantly impact the quality of life of millions of patients a year. These infections pose substantial clinical challenges, particularly as the currently available antifungal treatment options are limited in efficacy and often toxic. Azoles are a mainstay of antifungal therapy and work by targeting the biosynthesis of ergosterol. However, there are rising rates of acquired azole resistance in various Candida species, and some species are considered intrinsically resistant to most azoles. Our research demonstrates the promising therapeutic potential of synergistically enhancing azoles with non-toxic, FDA-approved bisphosphonates. Repurposing bisphosphonates as antifungal synergists can bypass much of the drug development pipeline and accelerate the translation of azole-bisphosphonate combination therapy.

A novel diterpenic derivative produced by Streptomyces chrestomyceticus ADP4 is a potent inhibitor of biofilm and virulence factors in Candida albicans and C. auris

AIM

Isolation, identification, structural and functional characterization of potent anti-Candida compound with specific antagonistic activities against significant human pathogens, Candida albicans and C. auris.

METHODS AND RESULTS

The compound (55B3) was purified from the metabolites produced by Streptomyces chrestomyceticus ADP4 by employing column chromatography. The structure of 55B3 was determined from the analyses of spectral data that included LCMS, nuclear magnetic resonance, FTIR, and UV spectroscopies. It was identified as a novel derivative of diterpenic aromatic acid, 3-(dictyotin-11'-oate-15'α, 19'β-olide)-4-(dictyotin-11'-oate-15″α, 19″β-olide)-protocatechoic acid. The compound displayed potent antifungal and anti-biofilm activities against C. albicans ATCC 10231 (Minimum Inhibitory Concentration, MIC90:14.94 ± 0.17 μgmL-1 and MBIC90: 16.03 ± 1.1 μgmL-1) and against C. auris CBS 12372 (MIC90: 21.75 ± 1.5 μgmL-1 and Minimum Biofilm Inhibitory Concentration, MBIC90: 18.38 ± 1.78 μgmL-1). Further, pronounced inhibition of important virulence attributes of Candida spp., e.g. yeast-to-hyphae transition, secretory aspartyl proteinase and phospholipase B by 55B3 was noted at subinhibitory concentrations. A plausible mechanism of anti-Candida action of the compound appeared to be the inhibition of ergosterol biosynthesis, which was inhibited by 64 ± 3% at the MIC90 value. The non-cytotoxic attribute of the compound was noted in the liver cell line (HepG2 cells).

CONCLUSION

The present work led to the discovery of a novel diterpenic derivative produced by S. chrestomyceticus ADP4. The compound displayed potent anti-Candida activity, particularly against the two most significant human pathogens, C. albicans and C. auris, which underlined its significance as a potential drug candidate for infections involving these pathogens.

Comparative analysis of enzymatic profiles and biofilm formation in clinical and environmental Candida kefyr isolates

The global landscape of Candida infections has seen a significant shift. Previously, Candida albicans was the predominant species. However, there has been an emergence of non-albicans Candida species, which are often less susceptible to antifungal treatment. Candida kefyr, in particular, has been increasingly associated with infections. This study aimed to investigate the profiles of enzymatic activity and biofilm formation in both clinical and non-clinical isolates of C. kefyr. A total of 66 C. kefyr isolates were analysed. The activities of proteinase and phospholipase were assessed using bovine serum albumin and egg yolk agar, respectively. Haemolysin, caseinolytic and esterase activities were evaluated using specific methods. Biofilm formation was investigated using crystal violet staining. The findings indicated that biofilm and proteinase activity were detected in 81.8% and 93.9% of all the isolates, respectively. Haemolysin activity was observed with the highest occurrence (95.5%) among normal microbiota isolates. Esterase activity was predominantly identified in dairy samples and was absent in hospital samples. Caseinase production was found with the highest occurrence (18.2%) in normal microbiota and hospital samples. Phospholipase activity was limited, found in only 3% of all the isolates. These findings reveal variations in enzyme activity between clinical and non-clinical C. kefyr isolates. This sheds light on their pathogenic potential and has implications for therapeutic strategies.

A new polycyclic tetramate macrolactam from Allostreptomyces RD068384: stereochemistry and antifungal potential

A new polycyclic tetramate macrolactam designated allostreptamide (1), together with four known congeners, were isolated from the culture extract of Allostreptomyces RD068384. The planar structure of the new compound was elucidated through interpretation of NMR and MS data. The absolute configuration was determined through ROESY and ECD analyses. The isolated compounds revealed antifungal potential against fourteen Candida albicans isolates with minimum inhibitory concentrations (MICs) ranging from 64 to 2048 µg ml-1. Compound 3 showed antibiofilm action and considerably reduced the viability of five isolates (36%) in the formed biofilm. The qRT-PCR revealed that 3 downregulated the BCR1, PLB2, ALS1, and SAP5 biofilm related gene expression. Therefore, 3 could be a promising antifungal therapy for C. albicans infections.

Microbial Biofilm Inhibition Using Magnetic Cross-Linked Polyphenol Oxidase Aggregates

Microbial biofilm accumulation poses a serious threat to the environment, presents significant challenges to different industries, and exhibits a large impact on public health. Since there has not been a conclusive answer found despite various efforts, the potential green and economical methods are being focused on, particularly the innovative approaches that employ biochemical agents. In the present study, we propose a bio-nanotechnological method using magnetic cross-linked polyphenol oxidase aggregates (PPO m-CLEA) for inhibition of microbial biofilm including multidrug resistant bacteria. Free PPO solution showed only 55-60% biofilm inhibition, whereas m-CLEA showed 70-75% inhibition, as confirmed through microscopic techniques. The carbohydrate and protein contents in biofilm extracellular polymeric substances (EPSs) were reduced significantly. The m-CLEA demonstrated reusability up to 5 cycles with consistent efficiency in biofilm inhibition. Computational work was also done where molecular docking of PPO with microbial proteins associated with biofilm formation was conducted, resulting in favorable binding scores and inter-residual interactions. Overall, both in vitro and in silico results suggest that PPO interferes with microbial cell attachment and EPS formation, thereby preventing biofilm colonization.

Disruption of Biofilm by Bacteriophages in Clinically Relevant Settings

INTRODUCTION

Antibiotic-resistant bacteria are a growing threat to civilian and military health today. Although infections were once easily treatable by antibiotics and wound cleaning, the frequent mutation of bacteria has created strains impermeable to antibiotics and physical attack. Bacteria further their pathogenicity because of their ability to form biofilms on wounds, medical devices, and implant surfaces. Methods for treating biofilms in clinical settings are limited, and when formed by antibiotic-resistant bacteria, can generate chronic infections that are recalcitrant to available therapies. Bacteriophages are natural viral predators of bacteria, and their ability to rapidly destroy their host has led to increased attention in potential phage therapy applications.

MATERIALS AND METHODS

The present article sought to address a knowledge gap in the available literature pertaining to the usage of bacteriophage in clinically relevant settings and the resolution of infections particular to military concerns. PRISMA guidelines were followed for a systematic review of available literature that met the criteria for analysis and inclusion. The research completed for this review article originated from the U.S. Military Academy's library "Scout" search engine, which complies results from 254 available databases (including PubMed, Google Scholar, and SciFinder). The search criteria included original studies that employed bacteriophage use against biofilms, as well as successful phage therapy strategies for combating chronic bacterial infections. We specifically explored the use of bacteriophage against antibiotic- and treatment-resistant bacteria.

RESULTS

A total of 80 studies were identified that met the inclusion criteria following PRISMA guidelines. The application of bacteriophage has been demonstrated to robustly disrupt biofilm growth in wounds and on implant surfaces. When traditional therapies have failed to disrupt biofilms and chronic infections, a combination of these treatments with phage has proven to be effective, often leading to complete wound healing without reinfection.

CONCLUSIONS

This review article examines the available literature where bacteriophages have been utilized to treat biofilms in clinically relevant settings. Specific attention is paid to biofilms on implant medical devices, biofilms formed on wounds, and clinical outcomes, where phage treatment has been efficacious. In addition to the clinical benefit of phage therapies, the military relevance and treatment of combat-related infections is also examined. Phages offer the ability to expand available treatment options in austere environments with relatively low cost and effort, allowing the impacted warfighter to return to duty quicker and healthier.

Antifungal activity of bio-active cell-free culture extracts and volatile organic compounds (VOCs) synthesised by endophytic fungal isolates of Garden Nasturtium

Antimicrobial resistance in fungal pathogens (both human and plant) is increasing alarmingly, leading to massive economic crises. The existing anti-fungal agents are becoming ineffective, and the situation worsens on a logarithmic scale. Novel antifungals from unique natural sources are highly sought to cope sustainably with the situation. Metabolites from endophytic microbes are the best-fitted alternatives in this case. Endophytes are the untapped sources of 'plants' internal microbial population' and are promising sources of effective bio-therapeutic agents. Fungal endophytes were isolated from Tropaeolum majus and checked for antifungal activity against selected plant and human pathogens. Bioactive metabolites were identified through chromatographic techniques. The mode of action of those metabolites was evaluated through various spectroscopic techniques. The production of antifungal metabolite was optimized also. In particular VOCs (volatile organic compounds) of TML9 were tested in vitro for their anti-phytopathogenic activity. Ethyl acetate (EA) extract of cell-free culture components of Colletotrichum aenigma TML3 exhibited broad-spectrum antifungal activity against four species of Candida and the major constituents reported were 6-pentyl-2H-pyran-2-one, 2-Nonanone, 1 propanol 2-amino. The volatile metabolites, trans-ocimene, geraniol, and 4-terpinyl acetate, produced from Curvularia lunata TML9, inhibited the growth of some selected phyto pathogens. EA extract hampered the biofilm formation, minimised the haemolytic effect, and blocked the transformation of Candida albicans (MTCC 4748) from yeast to hyphal form with a Minimum Fungicidal Concentration (MFC) of 200-600 µg mL-1. Central carbohydrate metabolism, ergosterol synthesis, and membrane permeability were adversely affected and caused the lethal leakage of necessary macromolecules of C. albicans. Volatile metabolites inhibited the growth of phytopathogens i.e., Rhizoctonia solani, Alternaria alternata, Botrytis cinerea, Cercospora beticola, Penicillium digitatum, Aspergillus fumigatus, Ceratocystis ulmi, Pythium ultimum up to 89% with an IC50 value of 21.3-69.6 µL 50 mL-1 and caused leakage of soluble proteins and other intracellular molecules. Citrusy sweet odor volatiles of TML9 cultured in wheat-husk minimised the infections of Penicillium digitatum (green mold), in VOC-exposed sweet oranges (Citrus sinensis). Volatile and non-volatile antifungal metabolites of these two T. majus endophytes hold agricultural and pharmaceutical interests. Metabolites of TML3 have strong anti-Candida activity and require further assessment for therapeutic applications. Also, volatile metabolites of TML9 can be further studied as a source of antifungals. The present investigational outcomes bio-prospects the efficacy of fungal endophytes of Garden Nasturtium.

Surfactants' Interplay with Biofilm Development in Staphylococcus and Candida

The capacity of micro-organisms to form biofilms is a pervasive trait in the microbial realm. For pathogens, biofilm formation serves as a virulence factor facilitating successful host colonization. Simultaneously, infections stemming from biofilm-forming micro-organisms pose significant treatment challenges due to their heightened resistance to antimicrobial agents. Hence, the quest for active compounds capable of impeding microbial biofilm development stands as a pivotal pursuit in biomedical research. This study presents findings concerning the impact of three surfactants, namely, polysorbate 20 (T20), polysorbate 80 (T80), and sodium dodecyl sulfate (SDS), on the initial stage of biofilm development in both Staphylococcus aureus and Candida dubliniensis. In contrast to previous investigations, we conducted a comparative assessment of the biofilm development capacity of these two taxonomically distant groups, predicated on their shared ability to reduce TTC. The common metabolic trait shared by S. aureus and C. dubliniensis in reducing TTC to formazan facilitated a simultaneous evaluation of biofilm development under the influence of surfactants across both groups. Our results revealed that surfactants could impede the development of biofilms in both species by disrupting the initial cell attachment step. The observed effect was contingent upon the concentration and type of compound, with a higher inhibition observed in culture media supplemented with SDS. At maximum concentrations (5%), T20 and T80 significantly curtailed the formation and viability of S. aureus and C. dubliniensis biofilms. Specifically, T20 inhibited biofilm development by 75.36% in S. aureus and 71.18% in C. dubliniensis, while T80 exhibited a slightly lower inhibitory effect, with values ranging between 66.68% (C. dubliniensis) and 65.54% (S. aureus) compared to the controls. Incorporating these two non-toxic surfactants into pharmaceutical formulations could potentially enhance the inhibitory efficacy of selected antimicrobial agents, particularly in external topical applications.

Butyl isothiocyanate exhibits antifungal and anti-biofilm activity against Candida albicans by targeting cell membrane integrity, cell cycle progression and oxidative stress

The prevalence of Candida albicans infection has increased during the past few years, which contributes to the need for new, effective treatments due to the increasing concerns regarding antifungal drug toxicity and multidrug resistance. Butyl isothiocyanate (butylITC) is a glucosinolate derivative, and has shown a significant antifungal effect contrary to Candida albicans. Additionally, how butylITC affects the virulence traits of C. albicans and molecular mode of actions are not well known. Present study shows that at 17.36 mM concentration butylITC inhibit planktonic growth. butylITC initially slowed the hyphal transition at 0.542 mM concentration. butylITC hampered biofilm development, and inhibits biofilm formation at 17.36 mM concentration which was analysed using metabolic assay (XTT assay) and Scanning Electron Microscopy (SEM). In addition, it was noted that butylITC inhibits ergosterol biosynthesis. The permeability of cell membranes was enhanced by butylITC treatment. Moreover, butylITC arrests cells at S-phase and induces intracellular Reactive Oxygen Species (ROS) accumulation in C. albicans. The results suggest that butylITC may have a dual mode of action, inhibit virulence factors and modulate cellular processes like inhibit ergosterol biosynthesis, cell cycle arrest, induces ROS production which leads to cell death in C. albicans.

Optimization of the antifungal properties of the bacterial peptide EntV by variant analysis

Fungal resistance to commonly used medicines is a growing public health threat, and there is a dire need to develop new classes of antifungals. We previously described a peptide produced by Enterococcus faecalis, EntV, that restricts Candida albicans to a benign form rather than having direct fungicidal activity. Moreover, we showed that one 12-amino acid (aa) alpha helix of this peptide retained full activity, with partial activity down to the 10aa alpha helix. Using these peptides as a starting point, the current investigation sought to identify the critical features necessary for antifungal activity and to screen for new variants with enhanced activity using both biofilm and C. elegans infection assays. First, the short peptides were screened for residues with critical activity by generating alanine substitutions. Based on this information, we used synthetic molecular evolution (SME) to rationally vary the specific residues of the 10aa variant in combination to generate a library that was screened to identify variants with more potent antifungal activity than the parent template. Five gain-of-function peptides were identified. Additionally, chemical modifications to the peptides to increase stability, including substitutions of D-amino acids and hydrocarbon stapling, were investigated. The most promising peptides were additionally tested in mouse models of oropharyngeal and systemic candidiasis where their efficacy in preventing infection was demonstrated. The expectation is that these discoveries will contribute to the development of new therapeutics in the fight against antimicrobial resistant fungi.

IMPORTANCE

Since the early 1980s, the incidence of disseminated life-threatening fungal infections has been on the rise. Worldwide, Candida and Cryptococcus species are among the most common agents causing these infections. Simultaneously, with this rise of clinical incidence, there has also been an increased prevalence of antifungal resistance, making treatment of these infections very difficult. For example, there are now strains of Candida auris that are resistant to all three classes of currently used antifungal drugs. In this study, we report on a strategy that allows for the development of novel antifungal agents by using synthetic molecular evolution. These discoveries demonstrate that the enhancement of antifungal activity from naturally occurring peptides is possible and can result in clinically relevant agents that have efficacy in multiple in vivo models as well as the potential for broad-spectrum activity.

Antifungal activity of nisin against clinical isolates of azole-resistant Candida tropicalis

The rapid emergence of invasive infections caused by azole-resistant Candida tropicalis has become a public health concern, and there is an urgent need for alternative treatment strategies. Studies have demonstrated the antibacterial effects of nisin, a well-known peptide naturally produced by Lactococcus lactis subsp. lactis. However, there is scant information about the antifungal effect of nisin against C. tropicalis. The present study aims to investigate the in vitro antifungal activity of nisin against clinical isolates of azole-resistant C. tropicalis strains, as well as its inhibitory effect on biofilm formation. A total of 35 C. tropicalis strains isolated from patients with invasive fungal infections were divided into the azole-resistant group and the azole-sensitive group, containing 21 and 14 strains, respectively. The relative expression levels of the ERG11 and UPC2 genes in the azole-resistant group were higher than those in the azole-sensitive group (p < 0.0001), while no significant differences were observed in the expression levels of the MDR1 and CDR1 genes. The minimum inhibitory concentration of nisin against C. tropicalis ranged from 2 to 8 μg/mL. Nisin treatment inhibited the growth of azole-resistant C. tropicalis, with over a four-fold reduction in OD600 nm values observed at the 8-h time point, while it promoted the transition of C. tropicalis from the spore phase to the hyphal phase, as observed on cryo-scanning electron microscopy. The results of biofilm quantification using crystal violet staining indicated a significant decrease in OD570 nm values in the nisin-treated group compared to the controls (p < 0.0001). Among the 21 azole-resistant C. tropicalis strains, the biofilm formation was inhibited in 17 strains (17/21, 81%), and more than 85% inhibition of biofilm formation was observed in the representative strains. With regard to the molecular mechanisms, the expression of the BCR1 and UPC2 genes in the azole-resistant strains was down-regulated on nisin treatment (p < 0.05). In conclusion, we demonstrated, for the first time, that nisin has antifungal activity and significant anti-biofilm activity against clinical isolates of azole-resistant C. tropicalis strains. Based on the findings, nisin could be a promising alternative antifungal agent for combating azole-resistant C. tropicalis infections.

An improved expression and purification protocol enables the structural characterization of Mnt1, an antifungal target from Candida albicans

BACKGROUND

Candida albicans is one of the most prevalent fungi causing infections in the world. Mnt1 is a mannosyltransferase that participates in both the cell wall biogenesis and biofilm growth of C. albicans. While the cell wall performs crucial functions in pathogenesis, biofilm growth is correlated with sequestration of drugs by the extracellular matrix. Therefore, antifungals targeting CaMnt1 can compromise fungal development and potentially also render Candida susceptible to drug therapy. Despite its importance, CaMnt1 has not yet been purified to high standards and its biophysical properties are lacking.

RESULTS

We describe a new protocol to obtain high yield of recombinant CaMnt1 in Komagataella phaffii using methanol induction. The purified protein's identity was confirmed by MALDI-TOF/TOF mass spectroscopy. The Far-UV circular dichroism (CD) spectra demonstrate that the secondary structure of CaMnt1 is compatible with a protein formed by α-helices and β-sheets at pH 7.0. The fluorescence spectroscopy results show that the tertiary structure of CaMnt1 is pH-dependent, with a greater intensity of fluorescence emission at pH 7.0. Using our molecular modeling protocol, we depict for the first time the ternary complex of CaMnt1 bound to its two substrates, which has enabled the identification of residues involved in substrate specificity and catalytic reaction. Our results corroborate the hypothesis that Tyr209 stabilizes the formation of an oxocarbenium ion-like intermediate during nucleophilic attack of the acceptor sugar, opposing the double displacement mechanism proposed by other reports.

CONCLUSIONS

The methodology presented here can substantially improve the yield of recombinant CaMnt1 expressed in flask-grown yeasts. In addition, the structural characterization of the fungal mannosyltransferase presents novelties that can be exploited for new antifungal drug's development.

Biofilm-associated metabolism via ERG251 in Candida albicans

Biofilm formation by the fungal pathogen Candida albicans is the basis for its ability to infect medical devices. The metabolic gene ERG251 has been identified as a target of biofilm transcriptional regulator Efg1, and here we report that ERG251 is required for biofilm formation but not conventional free-living planktonic growth. An erg251Δ/Δ mutation impairs biofilm formation in vitro and in an in vivo catheter infection model. In both in vitro and in vivo biofilm contexts, cell number is reduced and hyphal length is limited. To determine whether the mutant defect is in growth or some other aspect of biofilm development, we examined planktonic cell features in a biofilm-like environment, which was approximated with sealed unshaken cultures. Under those conditions, the erg251Δ/Δ mutation causes defects in growth and hyphal extension. Overexpression in the erg251Δ/Δ mutant of the paralog ERG25, which is normally expressed more weakly than ERG251, partially improves biofilm formation and biofilm hyphal content, as well as growth and hyphal extension in a biofilm-like environment. GC-MS analysis shows that the erg251Δ/Δ mutation causes a defect in ergosterol accumulation when cells are cultivated under biofilm-like conditions, but not under conventional planktonic conditions. Overexpression of ERG25 in the erg251Δ/Δ mutant causes some increase in ergosterol levels. Finally, the hypersensitivity of efg1Δ/Δ mutants to the ergosterol inhibitor fluconazole is reversed by ERG251 overexpression, arguing that reduced ERG251 expression contributes to this efg1Δ/Δ phenotype. Our results indicate that ERG251 is required for biofilm formation because its high expression levels are necessary for ergosterol synthesis in a biofilm-like environment.

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.

In vitro Evaluation of Fungal Susceptibility and Inhibition of Virulence by Diosgenin

Fungal infections are a public health problem that mainly affects immunosuppressed people, Candida spp. have been responsible for most sources of contamination and invasive fungal infections described around the world. The need arises to find new therapeutic approaches to combat growing infections. Plants and natural products have been considered a valuable source for discovering new molecules with active ingredients. Diosgenin is a sapogenin found in the families of Leguminosae and Dioscoreaceae, it is obtained mainly from the dioscin saponin through the hydrolysis method, it is a phytochemical that has been highlighted in the treatment of various diseases, as well as in combating microbial resistance. The present study aimed to evaluate the susceptibility of fungal strains to diosgenin, as well as verify the association with the reference drug and evaluate the inhibition of the virulence factor through morphological changes in the yeast state to the filamentous form of hyphae and pseudohyphae in strains of Candida albicans, Candida tropicalis and Candida krusei using the broth microdilution method and microculture technique. Antifungal assays revealed that diosgenin was not able to inhibit the growth of the tested strains. However, it was able to inhibit the fungal dimorphism of the strains evaluated, however further studies are recommended to verify its effectiveness against other virulence factors.

Two promising Bacillus-derived antifungal lipopeptide leads AF4 and AF5 and their combined effect with fluconazole on the in vitro Candida glabrata biofilms

Introduction: Candida species are endowed with the ability to produce biofilms, which is one of the causes of pathogenicity, as biofilms protect yeasts from antifungal drugs. Candida glabrata (Nakaseomyces glabrata) is one of the most prevalent pathogenic yeasts in humans and a biofilm producer. Methods: The study was aimed at evaluating the combined effects of two highly promising antifungal biomolecules (AF4 and AF5) lipopeptide in nature, chromatographically purified to homogeneity from Bacillus subtilis (B. subtilis) and the standard antifungal fluconazole (at different concentrations) to demonstrate C. glabrata biofilm formation inhibition. Biofilm production and inhibition were evaluated by quantification of the biofilm biomass and metabolic activity using crystal violet (CV) staining and XTT reduction assays, respectively. Microscopic techniques such as confocal scanning laser microscopy (CSLM) and scanning electron microscopy (SEM) were employed to visualize biofilm formation and inhibition. Results and Discussion: Compared to untreated and fluconazole-treated biofilms, an enhanced in vitro anti-biofilm effect of the antifungal lipopeptides AF4/AF5 alone and their combinations with fluconazole was established. The lipopeptides AF4/AF5 alone at 8 and 16 μg/mL exhibited significant biomass and metabolic activity reductions. SEM and CSLM images provided evidence that the lipopeptide exposure results in architectural alterations and a significant reduction of C. glabrata biofilms, whereas (2', 7'-dichlorofluorescin diacetate (DCFDA) and propidium iodide (PI) analyses showed reactive oxygen species (ROS) generation along with membrane permeabilization. The estimation of exopolysaccharides (EPS) in AF4/AF5-treated biofilms indicated EPS reduction. The combinations of fluconazole (64/128 μg/mL) and AF4/AF5 lipopeptide (16 μg/mL) were found to significantly disrupt the mature (24 h) biofilms as revealed by CSLM and SEM studies. The CSLM images of biofilms were validated using COMSTAT. The FTIR-analyses indicate the antibiofilm effects of both lipopeptides on 24 h biofilms to support CSLM and SEM observations. The combinations of fluconazole (64/128 μg/mL) and AF4/AF5 lipopeptide were found to disrupt the mature biofilms; the study also showed that the lipopeptides alone have the potentials to combat C. glabrata biofilms. Taken together, it may be suggested that these lipopeptide leads can be optimized to potentially apply on various surfaces to either reduce or nearly eradicate yeast biofilms.

Stephanoascus ciferrii Complex: The Current State of Infections and Drug Resistance in Humans

In recent years, the incidence of fungal infections in humans has increased dramatically, accompanied by an expansion in the number of species implicated as etiological agents, especially environmental fungi never involved before in human infection. Among fungal pathogens, Candida species are the most common opportunistic fungi that can cause local and systemic infections, especially in immunocompromised individuals. Candida albicans (C. albicans) is the most common causative agent of mucosal and healthcare-associated systemic infections. However, during recent decades, there has been a worrying increase in the number of emerging multi-drug-resistant non-albicans Candida (NAC) species, i.e., C. glabrata, C. parapsilosis, C. tropicalis, C. krusei, C. auris, and C. ciferrii. In particular, Candida ciferrii, also known as Stephanoascus ciferrii or Trichomonascus ciferrii, is a heterothallic ascomycete yeast-like fungus that has received attention in recent decades as a cause of local and systemic fungal diseases. Today, the new definition of the S. ciferrii complex, which consists of S. ciferrii, Candida allociferrii, and Candida mucifera, was proposed after sequencing the 18S rRNA gene. Currently, the S. ciferrii complex is mostly associated with non-severe ear and eye infections, although a few cases of severe candidemia have been reported in immunocompromised individuals. Low susceptibility to currently available antifungal drugs is a rising concern, especially in NAC species. In this regard, a high rate of resistance to azoles and more recently also to echinocandins has emerged in the S. ciferrii complex. This review focuses on epidemiological, biological, and clinical aspects of the S. ciferrii complex, including its pathogenicity and drug resistance.

Biofilm inhibition/eradication: exploring strategies and confronting challenges in combatting biofilm

Biofilms are complex communities of microorganisms enclosed in a self-produced extracellular matrix, posing a significant threat to different sectors, including healthcare and industry. This review provides an overview of the challenges faced due to biofilm formation and different novel strategies that can combat biofilm formation. Bacteria inside the biofilm exhibit increased resistance against different antimicrobial agents, including conventional antibiotics, which can lead to severe problems in livestock and animals, including humans. In addition, biofilm formation also imposes heavy economic pressure on industries. Hence it becomes necessary to explore newer alternatives to eradicate biofilms effectively without applying selection pressure on the bacteria. Excessive usage of antibiotics may also lead to an increase in the number of resistant strains as bacteria employ an advanced antimicrobial resistance mechanism. This review provides insight into multifaceted technologies like quorum sensing inhibition, enzymes, antimicrobial peptides, bacteriophage, phytocompounds, and nanotechnology to neutralize biofilms without developing antimicrobial resistance (AMR). Furthermore, it will pave the way for developing newer therapeutic agents to deal with biofilms more efficiently.

Pathophysiological microenvironments in oral candidiasis

Oral candidiasis (OC), a prevalent opportunistic infection of the oral mucosa, presents a considerable health challenge, particularly in individuals with compromised immune responses, advanced age, and local predisposing conditions. A considerable part of the population carries Candida in the oral cavity, but only few develop OC. Therefore, the pathogenesis of OC may depend on factors other than the attributes of the fungus, such as host factors and other predisposing factors. Mucosal trauma and inflammation compromise epithelial integrity, fostering a conducive environment for fungal invasion. Molecular insights into the immunocompromised state reveal dysregulation in innate and adaptive immunity, creating a permissive environment for Candida proliferation. Detailed examination of Candida species (spp.) and their virulence factors uncovers a nuanced understanding beyond traditional C. albicans focus, which embrace diverse Candida spp. and their strategies, influencing adhesion, invasion, immune evasion, and biofilm formation. Understanding the pathophysiological microenvironments in OC is crucial for the development of targeted therapeutic interventions. This review aims to unravel the diverse pathophysiological microenvironments influencing OC development focusing on microbial, host, and predisposing factors, and considers Candida resistance to antifungal therapy. The comprehensive approach offers a refined perspective on OC, seeking briefly to identify potential therapeutic targets for future effective management.

The antimicrobial property of JY-1, a complex mixture of Traditional Chinese Medicine, is linked to it abilities to suppress biofilm formation and disrupt membrane permeability

The substantial increase of infections, caused by novel, sudden, and drug-resistant pathogens, poses a significant threat to human health. While numerous studies have demonstrated the antibacterial and antiviral effects of Traditional Chinese Medicine, the potential of a complex mixture of traditional Chinese Medicine with a broad-spectrum antimicrobial property remains underexplored. This study aimed to develop a complex mixture of Traditional Chinese Medicine (TCM), JY-1, and investigate its antimicrobial properties, along with its potential mechanism of action against pathogenic microorganisms. Antimicrobial activity was assessed using a zone of inhibition assay and the drop plate method. Hyphal induction of Candida albicans was conducted using RPMI1640 medium containing 10% FBS, followed by microscopic visualization. Quantitative real-time PCR (RT-qPCR) was employed to quantify the transcript levels of hyphal-specific genes such as HWP1 and ALS3. The impact of JY-1 on biofilm formation was evaluated using both the XTT reduction assay and scanning electron microscopy (SEM). Furthermore, the cell membrane integrity was assessed by protein and nucleic acid leakage assays. Our results clearly showed that JY-1 significantly inhibits the vegetative growth of Candida spp. and Cryptococcus spp. In addition, this complex mixture is effectively against a wide range of pathogenic bacteria, including Staphylococcus aureus, Vancomycin-resistant enterococci, Escherichia coli, Klebsiella pneumoniae and Enterobacter cloacae. More interestingly, JY-1 plays a direct anti-viral role against the mammalian viral pathogen vesicular stomatitis virus (VSV). Further mechanistic studies indicate that JY-1 acts to reduce the expression of hyphal specific genes HWP1 and ALS3, resulting in the suppression of the hyphal formation of C. albicans. The antimicrobial property of JY-1 could be attributed to its ability to reduce biofilm formation and disrupt the cell membrane permeability, a process resulting in microbial cell death and the release of cellular contents. Taken together, our work identified a potent broad-spectrum antimicrobial agent, a complex mixture of TCM which might be developed as a potential antimicrobial drug.

Candidemia in Adult Patients in the ICU: A Reappraisal of Susceptibility Testing and Antifungal Therapy

OBJECTIVE

To provide updates on the epidemiology and recommendations for management of candidemia in patients with critical illness.

DATA SOURCES

A literature search using the PubMed database (inception to March 2023) was conducted using the search terms "invasive candidiasis," "candidemia," "critically ill," "azoles," "echinocandin," "antifungal agents," "rapid diagnostics," "antifungal susceptibility testing," "therapeutic drug monitoring," "antifungal dosing," "persistent candidemia," and "Candida biofilm."

STUDY SELECTION/DATA EXTRACTION

Clinical data were limited to those published in the English language. Ongoing trials were identified through ClinicalTrials.gov.

DATA SYNTHESIS

A total of 109 articles were reviewed including 25 pharmacokinetic/pharmacodynamic studies and 30 studies including patient data, 13 of which were randomized controlled clinical trials. The remaining 54 articles included fungal surveillance data, in vitro studies, review articles, and survey data. The current 2016 Infectious Diseases Society of America (IDSA) Clinical Practice Guideline for the Management of Candidiasis provides recommendations for selecting empiric and definitive antifungal therapies for candidemia, but data are limited regarding optimized dosing strategies in critically ill patients with dynamic pharmacokinetic changes or persistent candidemia complicated.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

Outcomes due to candidemia remain poor despite improved diagnostic platforms, antifungal susceptibility testing, and antifungal therapy selection for candidemia in critically ill patients. Earlier detection and identification of the species causing candidemia combined with recognition of patient-specific factors leading to dosing discrepancies are crucial to improving outcomes in critically ill patients with candidemia.

CONCLUSIONS

Treatment of candidemia in critically ill patients must account for the incidence of non-albicans Candida species and trends in antifungal resistance as well as overcome the complex pathophysiologic changes to avoid suboptimal antifungal exposure.

Nanozyme-Based Robotics Approach for Targeting Fungal Infection

Fungal pathogens have been designated by the World Health Organization as microbial threats of the highest priority for global health. It remains a major challenge to improve antifungal efficacy at the site of infection while avoiding off-target effects, fungal spreading, and drug tolerance. Here, a nanozyme-based microrobotic platform is developed that directs localized catalysis to the infection site with microscale precision to achieve targeted and rapid fungal killing. Using electromagnetic field frequency modulation and fine-scale spatiotemporal control, structured iron oxide nanozyme assemblies are formed that display tunable dynamic shape transformation and catalysis activation. The catalytic activity varies depending on the motion, velocity, and shape providing controllable reactive oxygen species (ROS) generation. Unexpectedly, nanozyme assemblies bind avidly to fungal (Candida albicans) surfaces to enable concentrated accumulation and targeted ROS-mediated killing in situ. By exploiting these tunable properties and selective binding to fungi, localized antifungal activity is achieved using in vivo-like cell spheroid and animal tissue infection models. Structured nanozyme assemblies are directed to Candida-infected sites using programmable algorithms to perform precisely guided spatial targeting and on-site catalysis resulting in fungal eradication within 10 min. This nanozyme-based microrobotics approach provides a uniquely effective and targeted therapeutic modality for pathogen elimination at the infection site.

Ecological competition in the oral mycobiome of Hispanic adults living in Puerto Rico associates with periodontitis

Background: Fungi are a major component of the human microbiome that only recently received attention. The imbalance of indigenous fungal communities and environmental fungi present in the oral cavity may have a role in oral dysbiosis, which could exacerbate oral inflammatory diseases. Methods: We performed a cross-sectional study and recruited 88 participants aged 21 to 49 from sexually transmitted infection clinics in Puerto Rico. A full-mouth periodontal examination following the NHANES protocol defined periodontal severity (CDC/AAP). ITS2 (fungal) genes were amplified and sequenced for mycobiota characterization of yeast and environmental fungi. Environmental outdoor spore levels were measured daily by the American Academy of Allergy Asthma and Immunology San Juan station and defined by quartiles as spore scores. Results: Our data indicate polymicrobial colonization of yeast and environmental fungi in the oral cavity. Dominant taxa associated with periodontal disease included Saccharomyces cerevisiae, Rigidoporus vinctus, and Aspergillus penicilloides, while Candida albicans were found to be ubiquitous. Fungal aerosols were found to impact the oral cavity biofilm, likely due to competition and neutralization by inhaled outdoor and indoor fungal spores. Conclusion: To our knowledge, this is the first report showcasing the ecological competition of measured outdoor environmental fungi with the human oral mycobiota.

Impact of Intravenous Fat Emulsion Choice on Candida Biofilm, Hyphal Growth, and Catheter-Related Bloodstream Infections in Pediatric Patients

BACKGROUND

Use of mixed-oil (MO) intravenous fat emulsion (IFE) was shown to inhibit Candida albicans biofilm formation and overall rate of catheter-related bloodstream infections (CR-BSIs) compared with soybean-oil (SO) IFE). We aimed to delineate this inhibitory mechanism and impact of IFE choice on distribution of fungal CR-BSIs.

METHODS

Transcriptional profiling was conducted on C. albicans grown in SO-IFE, MO-IFE, or SO-IFE with capric acid. Overexpression strains of shared down-regulated genes were constructed using a tetracycline-off system to assess hypha and biofilm formation in IFEs. A 5-year retrospective multicenter cohort study was performed to assess differences in CR-BSIs caused by Candida species based on the IFE formulation received in pediatric patients.

RESULTS

Genes significantly down-regulated in MO-IFE and SO-IFE with capric acid included CDC11, HGC1, and UME6. Overexpression of HGC1 or UME6 enabled filamentation in capric acid and MO-IFE. Interestingly, only overexpression of UME6 was sufficient to rescue biofilm growth in MO-IFE. MO-IFE administration was associated with a higher proportion of non-albicans Candida versus C. albicans CR-BSIs (42% vs 33%; odds ratio, 1.22 [95% confidence interval, .46-3.26]).

CONCLUSIONS

MO-IFE affects C. albicans biofilm formation and hyphal growth via a UME6-dependent mechanism. A numerical but not statistically significant difference in distribution of Candida spp. among CR-BSIs was observed.

Systematic identification and characterization of five transcription factors mediating the oxidative stress response in Candida albicans

Candida albicans is an opportunistic human fungal pathogen that causes superficial and systemic infections, particularly in immunocompromised individuals. In response to C. albicans infection, innate immune cells of the host produce and accumulate reactive oxygen species (ROS), which can lead to irreversible damage and apoptosis of fungal cells. Several transcription factors involved in this oxidative stress response have been identified; however, a systematic study to identify the transcription factors that mediate the oxidative stress response has not yet been conducted. Here, we screened a comprehensive transcription factor mutant library consisting of 211 transcription factor deletion mutant strains in the presence and absence of hydrogen peroxide (H2O2), a potent ROS inducer, and identified five transcription factors (Skn7, Dpb4, Cap1, Dal81, and Stp2) that are sensitive to H2O2. Genome-wide transcriptional profiling revealed that H2O2 induces a discrete set of differentially regulated genes among the five identified transcription factor mutant strains. Functional enrichment analysis identified KEGG pathways pertaining to glycolysis/gluconeogenesis, amino sugar and nucleotide sugar metabolism, and ribosome synthesis as the most enriched pathways. GO term analysis of the top common differentially expressed genes among the transcription factor mutant strains identified hexose catabolism and iron transport as the most enriched GO terms upon exposure to H2O2. This study is the first to systematically identify and characterise the transcription factors involved in the response to H2O2. Based on our transcriptional profiling results, we found that exposure to H2O2 modulates several downstream genes involved in fungal virulence. Overall, this study sheds new light on the metabolism, physiological functions, and cellular processes involved in the H2O2-induced oxidative stress response in C. albicans.

Bibliometric analysis and thematic review of Candida pathogenesis: Fundamental omics to applications as potential antifungal drugs and vaccines

Invasive candidiasis caused by the pathogenic Candida yeast species has resulted in elevating global mortality. The pathogenicity of Candida spp. is not only originated from its primary invasive yeast-to-hyphal transition; virulence factors (transcription factors, adhesins, invasins, and enzymes), biofilm, antifungal drug resistance, stress tolerance, and metabolic adaptation have also contributed to a greater clinical burden. However, the current research theme in fungal pathogenicity could hardly be delineated with the increasing research output. Therefore, our study analysed the research trends in Candida pathogenesis over the past 37 years via a bibliometric approach against the Scopus and Web of Science databases. Based on the 3993 unique documents retrieved, significant international collaborations among researchers were observed, especially between Germany (Bernhard Hube) and the UK (Julian Naglik), whose focuses are on Candida proteinases, adhesins, and candidalysin. The prominent researchers (Neils Gow, Alistair Brown, and Frank Odds) at the University of Exeter and the University of Aberdeen (second top performing affiliation) UK contribute significantly to the mechanisms of Candida adaptation, tolerance, and stress response. However, the science mapping of co-citation analysis performed herein could not identify a hub representative of subsequent work since the clusters were semi-redundant. The co-word analysis that was otherwise adopted, revealed three research clusters; the cluster-based thematic analyses indicated the severeness of Candida biofilm and antifungal resistance as well as the elevating trend on molecular mechanism elucidation for drug screening and repurposing. Importantly, the in vivo pathogen adaptation and interactions with hosts are crucial for potential vaccine development.

Features of the rare pathogen Meyerozyma guilliermondii strain SO and comprehensive in silico analyses of its adherence-contributing virulence factor agglutinin-like sequences

Meyerozyma guilliermondii is a rare yeast pathogen contributing to the deadly invasive candidiasis. M. guilliermondii strain SO, as a promising protein expression host, showed 99% proteome similarity with the clinically isolated ATCC 6260 (type strain) in a recent comparative genomic analysis. However, their in vitro virulence features and in vivo pathogenicity were uncharacterized. This study aimed to characterize the in vitro and in vivo pathogenicity of M. guilliermondii strain SO and analyze its Als proteins (MgAls) via comprehensive bioinformatics approaches. M. guilliermondii strain SO showed lower and higher sensitivity towards β-mercaptoethanol and lithium, respectively than the avirulent S. cerevisiae but exhibited the same tolerance towards cell wall-perturbing Congo Red with C. albicans. With 7.5× higher biofilm mass, M. guilliermondii strain SO also demonstrated 75% higher mortality rate in the zebrafish embryos with a thicker biofilm layer on the chorion compared to the avirulent S. cerevisiae. Being one of the most important Candida adhesins, sequence and structural analyses of four statistically identified MgAls showed that MgAls1056 was predicted to exhibit the most conserved amyloid-forming regions, tandem repeat domain and peptide binding cavity (PBC) compared to C. albicans Als3. Favoured from the predicted largest ligand binding site and druggable pockets, it showed the highest affinity towards hepta-threonine. Non-PBC druggable pockets in the most potent virulence contributing MgAls1056 provide new insights into developing antifungal drugs targeting non-albicans Candida spp. Virtual screening of available synthetic or natural bioactive compounds and MgAls1056 deletion from the fungal genome should be further performed and validated experimentally.Communicated by Ramaswamy H. Sarma.

Recent gene selection and drug resistance underscore clinical adaptation across Candida species

Understanding how microbial pathogens adapt to treatments, humans and clinical environments is key to infer mechanisms of virulence, transmission and drug resistance. This may help improve therapies and diagnostics for infections with a poor prognosis, such as those caused by fungal pathogens, including Candida. Here we analysed genomic variants across approximately 2,000 isolates from six Candida species (C. glabrata, C. auris, C. albicans, C. tropicalis, C. parapsilosis and C. orthopsilosis) and identified genes under recent selection, suggesting a highly complex clinical adaptation. These involve species-specific and convergently affected adaptive mechanisms, such as adhesion. Using convergence-based genome-wide association studies we identified known drivers of drug resistance alongside potentially novel players. Finally, our analyses reveal an important role of structural variants and suggest an unexpected involvement of (para)sexual recombination in the spread of resistance. Our results provide insights on how opportunistic pathogens adapt to human-related environments and unearth candidate genes that deserve future attention.

Green synthesis of biogenic selenium nanoparticles functionalized with ginger dietary extract targeting virulence factor and biofilm formation in Candida albicans

To treat the systemic infections caused by Candida albicans (C. albicans), various drugs have been used, however, infections still persisted due to virulence factors and increasing antifungal resistance. As a solution to this problem, we synthesized selenium nanoparticles (SeNPs) by using Bacillus cereus bacteria. This is the first study to report a higher (70 %) reduction of selenite ions into SeNPs in under 6 h. The as-synthesized, biogenic SeNPs were used to deliver bioactive constituents of aqueous extract of ginger for inhibiting the growth and biofilm (virulence factors) in C. albicans. UV-visible spectroscopy revealed a characteristic absorption at 280 nm, and Raman spectroscopy showed a characteristic peak shift at 253 cm-1 for the biogenic SeNPs. The synthesized SeNPs are spherical with 240-250 nm in size as determined by electron microscopy. Fourier transform infrared spectroscopy confirmed the functionalization of antifungal constituents of ginger over the SeNPs (formation of Ginger@SeNPs nanoconjugates). In contrast to biogenic SeNPs, nanoconjugates were active against C. albicans for inhibiting growth and biofilm formation. In order to reveal antifungal mechanism of nanoconjugates', real-time polymerase chain reaction (RT-PCR) analysis was performed, according to RT-PCR analysis, the nanoconjugates target virulence genes involved in C. albicans hyphae and biofilm formation. Nanoconjugates inhibited 25 % growth of human embryonic kidney (HEK) 293 cell line, indicating moderate cytotoxicity of active nanoconjugates in an in-vitro cytotoxicity study. Therefore, biogenic SeNPs conjugated with ginger dietary extract may be a potential antifungal agent and drug carrier for inhibiting C. albicans growth and biofilm formation.

ROS mediated anticandidal efficacy of 3-Bromopyruvate prevents vulvovaginal candidiasis in mice model

Candidal infections, particularly vulvovaginal candidiasis (VVC), necessitate effective therapeutic interventions in clinical settings owing to their intricate clinical nature and elusive understanding of their etiological mechanisms. Given the challenges in developing effective antifungal therapies, the strategy of repurposing existing pharmaceuticals has emerged as a promising approach to combat drug-resistant fungi. In this regard, the current study investigates molecular insights on the anti-candidal efficacy of a well-proven anticancer small molecule -3-bromopyruvate (3BP) against three clinically significant VVC causing Candida species viz., C. albicans, C. tropicalis and C. glabrata. Furthermore, the study validates 3BP's therapeutic application by developing it as a vaginal cream for the treatment of VVC. 3BP exhibited phenomenal antifungal efficacy (killing >99%) with minimum inhibitory concentrations (MIC) and minimum fungicidal concentrations (MFC) of 256 μg/mL against all tested Candida spp. Time killing kinetics experiment revealed 20 min as the minimum time required for 3BP at 2XMIC to achieve complete-killing (99.9%) in all Candida strains. Moreover, the ergosterol or sorbitol experiment explicated that the antifungal activity of 3BP does not stem from targeting the cell wall or the membrane component ergosterol. Instead, 3BP was observed to instigate a sequence of pre-apoptotic cascade events, such as phosphatidylserine (PS) externalization, nuclear condensation and ROS accumulations, as evidenced by PI, DAPI and DCFH-DA staining methods. Furthermore, 3BP demonstrated a remarkable efficacy in eradicating mature biofilms of Candida spp., achieving a maximum eradication level of 90%. Toxicity/safety profiling in both in vitro erythrocyte lysis and in vivo Galleria mellonella survival assay authenticated the non-toxic nature of 3BP up to 512 μg/mL. Finally, a vaginal cream formulated with 3BP was found to be effective in VVC-induced female mice model, as it significantly decreasing fungal load and protecting vaginal mucosa. Concomitantly, the present study serves as a clear demonstration of antifungal mechanistic action of anticancer drug -3BP, against Candida species. This finding holds significant potential for mitigating candidal infections, particularly VVC, within healthcare environments.

Increased Absorption and Inhibitory Activity against Candida spp. of Imidazole Derivatives in Synergistic Association with a Surface Active Agent

This paper's purpose was to evaluate the interaction between three imidazole derivatives, (2-methyl-1H-imidazol-1-yl)methanol (SAM3), 1,1'-methanediylbis(1H-benzimidazole (AM5) and (1H-benzo[d]imidazol-1-yl)methanol 1-hydroxymethylbenzimidazole (SAM5) on the one hand, and sodium dodecyl sulphate (SDS) on the other, as antifungal combinations against Candida spp. Inhibitory activity was assessed using the agar diffusion method and Minimal Inhibitory Concentration (MIC) and showed moderate inhibitory activity of single imidazole derivatives against Candida spp. The mean value of MIC ranged from 200 µg/mL (SAM3) to 312.5 µg/mL (SAM3), while for SDS the MIC was around 1000 µg/mL. When used in combination with SDS, the imidazole derivatives demonstrated an improvement in their antifungal activity. Their MIC decreased over five times for AM5 and over seven times for SAM3 and SAM5, respectively, and ranged from 26.56 µg/mL (SAM3) to 53.90 µg/mL (AM5). Most combinations displayed an additive effect while a clear synergistic effect was recorded in only a few cases. Thus, the FIC Index (FICI) with values between 0.311 and 0.375 showed a synergistic effect against Candida spp. when SDS was associated with SAM3 (three strains), SAM5 (two strains) and AM5 (one strain). The association of imidazole derivatives with SDS led to the increased release of cellular material as well as the intracellular influx of crystal violet (CV), which indicated an alteration of the membrane permeability of Candida spp. cells. This favored the synergistic effect via increasing the intracellular influx of imidazoles.

Discovery of Novel 8-Hydroxyquinoline Derivatives with Potent In Vitro and In Vivo Antifungal Activity

Fungal pathogens can cause life-threatening infections, yet current antifungals are inadequate at treating many of these, highlighting the importance of novel drug discovery. Here, we report hit compound L14, a novel 8-hydroxyquinoline derivative with potent and broad-spectrum antifungal activity. In vitro experiments exhibited that L14 had better activity and lower cytotoxicity than that of clioquinol and showed synergy in combination with fluconazole (FLC). In a Candida albicans-infected murine model, L14 at 2 mg/kg showed better in vivo efficacy than clioquinol at reducing fungal burden and extending the survival of C. albicans-infected mice. In addition, L14 alone or in combination with FLC had significant inhibitory activity against hypha and biofilm formation. Overall, our data indicated that 8-hydroxyquinoline derivative L14 has favorable pharmacokinetics and acceptable safety profiles and could be further investigated as a promising antifungal hit compound.

Tryptophol Improves the Biocontrol Efficacy of Scheffersomyces spartinae against the Gray Mold of Strawberries by Quorum Sensing

Previously, we reported that marine yeast Scheffersomyces spartinae exhibited biocontrol efficacy against the gray mold of strawberries caused by Botrytis cinerea. Herein, tryptophol, a quorum-sensing molecule, was identified in the metabolites of S. spartinae. Subsequently, we found that 25 μM tryptophol promoted population density, biofilm formation, and cell aggregation of S. spartinae. Furthermore, 25 μM tryptophol improved the biocontrol efficacy of S. spartinae against B. cinerea in vitro and in the strawberry fruit. Under a scanning electronic microscope, tryptophol facilitated colonization and biofilm formation on strawberry wounds, showing that tryptophol increased the biocontrol efficacy of S. spartinae via quorum sensing. Transcriptome analysis revealed that tryptophol upregulated the gene expression of SDS3, DAL81, DSE1, SNF5, SUN41, FLO8, and HOP1, which was associated with cell adhesion or biofilm formation. Thus, to the best of our knowledge, this study was the first to report that tryptophol improved the biocontrol efficacy of S. spartinae via quorum sensing.

In Vitro Susceptibility Tests in the Context of Antifungal Resistance: Beyond Minimum Inhibitory Concentration in Candida spp

Antimicrobial resistance is a matter of rising concern, especially in fungal diseases. Multiple reports all over the world are highlighting a worrisome increase in azole- and echinocandin-resistance among fungal pathogens, especially in Candida species, as reported in the recently published fungal pathogens priority list made by WHO. Despite continuous efforts and advances in infection control, development of new antifungal molecules, and research on molecular mechanisms of antifungal resistance made by the scientific community, trends in invasive fungal diseases and associated antifungal resistance are on the rise, hindering therapeutic options and clinical cures. In this context, in vitro susceptibility testing aimed at evaluating minimum inhibitory concentrations, is still a milestone in the management of fungal diseases. However, such testing is not the only type at a microbiologist's disposal. There are other adjunctive in vitro tests aimed at evaluating fungicidal activity of antifungal molecules and also exploring tolerance to antifungals. This plethora of in vitro tests are still left behind and performed only for research purposes, but their role in the context of invasive fungal diseases associated with antifungal resistance might add resourceful information to the clinical management of patients. The aim of this review was therefore to revise and explore all other in vitro tests that could be potentially implemented in current clinical practice in resistant and difficult-to-treat cases.

Exploring therapeutic avenues: mesenchymal stem/stromal cells and exosomes in confronting enigmatic biofilm-producing fungi

Fungal infections concomitant with biofilms can demonstrate an elevated capacity to withstand substantially higher concentrations of antifungal agents, contrasted with infectious diseases caused by planktonic cells. This inherent resilience intrinsic to biofilm-associated infections engenders a formidable impediment to effective therapeutic interventions. The different mechanisms that are associated with the intrinsic resistance of Candida species encompass drug sequestration by the matrix, drug efflux pumps, stress response cell density, and the presence of persister cells. These persisters, a subset of fungi capable of surviving hostile conditions, pose a remarkable challenge in clinical settings in virtue of their resistance to conventional antifungal therapies. Hence, an exigent imperative has arisen for the development of novel antifungal therapeutics with specific targeting capabilities focused on these pathogenic persisters. On a global scale, fungal persistence and their resistance within biofilms generate an urgent clinical need for investigating recently introduced therapeutic strategies. This review delves into the unique characteristics of Mesenchymal stem/stromal cells (MSCs) and their secreted exosomes, which notably exhibit immunomodulatory and regenerative properties. By comprehensively assessing the current literature and ongoing research in this field, this review sheds light on the plausible mechanisms by which MSCs and their exosomes can be harnessed to selectively target fungal persisters. Additionally, prospective approaches in the use of cell-based therapeutic modalities are examined, emphasizing the importance of further research to overcome the enigmatic fungal persistence.

Ethyl Isothiocyanate as a Novel Antifungal Agent Against Candida albicans

In the recent years, occurrence of candidiasis has increased drastically which leads to significant mortality and morbidity mainly in immune compromised patients. Glucosinolate (GLS) derivatives are reported to have antifungal activities. Ethyl isothiocyanate (EITC) and its antifungal activity and mechanism of action is still unclear against Candida albicans. The present work was designed to get a mechanistic insight in to the anti-Candida efficacy of EITC through in vitro and in vivo studies. EITC inhibited C. albicans planktonic growth at 0.5 mg/ml and virulence factors like yeast to hyphal form morphogenesis (0.0312 mg/ml), adhesion to polystyrene surface (0.0312 mg/ml) and biofilm formation (developing biofilm at 2 mg/ml and mature biofilm at 0.5 mg/ml) effectively. EITC blocked ergosterol biosynthesis and arrested C. albicans cells at S-phase. EITC caused ROS-dependent cellular death and nuclear or DNA fragmentation. EITC at 0.0312 mg/ml concentration regulated the expression of genes involved in the signal transduction pathway and inhibited yeast to hyphal form morphogenesis by upregulating TUP1, MIG1, and NRG1 by 3.10, 5.84 and 2.64-fold, respectively and downregulating PDE2 and CEK1 genes by 15.38 and 2.10-fold, respectively. EITC has showed haemolytic activity at 0.5 mg/ml concentration. In vivo study in silk worm model showed that EITC has toxicity to C. albicans at 0.5 mg/ml concentration. Thus, from present study we conclude that EITC has antifungal activity and to reduce its MIC and toxicity, combination study with other antifungal drugs need to be done. EITC and its combinations might be used as alternative therapeutics for the prevention and treatment of C. albicans infections.

Real-time monitoring of biofilm growth identifies andrographolide as a potent antifungal compound eradicating Candida biofilms

Candida species cause life-threatening infections with high morbidity and mortality rates and their resistance to conventional therapy is closely linked to biofilm formation. Thus, the development of new approaches to study Candida biofilms and the identification of novel therapeutic strategies could yield improved clinical outcomes. In the current study, we have set up an impedance-based in vitro system to study Candida spp. biofilms in real-time and to evaluate their sensitivity to two conventional antifungal groups used in clinical practice - azoles and echinocandins. Both fluconazole and voriconazole were unable to inhibit biofilm formation in most strains tested, while echinocandins showed biofilm inhibitory capacity at relatively low concentrations (starting from 0.625 mg/L). However, assays performed on 24 h Candida albicans and C. glabrata biofilms revealed that micafungin and caspofungin failed to eradicate mature biofilms at all tested concentrations, evidencing that once formed, Candida spp. biofilms are extremely difficult to eliminate using currently available antifungals. We then evaluated the antifungal and anti-biofilm effect of andrographolide, a natural compound isolated from the plant Andrographis paniculata with known antibiofilm activity on Gram-positive and Gram-negative bacteria. Optical density measures, impedance evaluation, CFU counts, and electron microscopy data showed that andrographolide strongly inhibits planktonic Candida spp. growth and halts Candida spp. biofilm formation in a dose-dependent manner in all tested strains. Moreover, andrographolide was capable of eliminating mature biofilms and viable cell numbers by up to 99.9% in the C. albicans and C. glabrata strains tested, suggesting its potential as a new approach to treat multi-resistant Candida spp. biofilm-related infections.

Biofilm Inhibition of Inula viscosa (L.) Aiton and Globularia alypum L. Extracts Against Candida Infectious Pathogens and In Vivo Action on Galleria mellonella Model

The increasing importance of fungal infections has fueled the search for new beneficial alternatives substance from plant extracts. The current study investigates the antifungal and antibiofilm activity of Inula viscosa (L.) Aiton and Globularia alypum (L.) leaves extracts against Candida both in vitro and in vivo. The inhibition of planktonic and sessile Candida albicans and Candida glabrata growth using both leaf extracts are evaluated. Moreover; an in vivo infection model using Galleria mellonella larvae; infected and treated with the extracts are performed. All extracts show fungicidal activity; with a minimum fungicidal concentration (MFC) ranging from 128 to 512 µg mL-1 against the two selected strains of Candida. In particular, the best results are obtained with methanolic extract of I. viscosa and G. alypum with an MFC value of 128 µg mL-1 . The extracts are capable to prevent 90% of biofilm development at minor concentrations ranging from 100.71 ± 2.49 µg mL-1 to 380.4 ± 0.92 µg mL-1 . In vivo, tests on Galleria mellonella larvae show that the extracts increase the survival of the larvae infected with Candida. The attained results reveal that I. viscosa and G. alypum extracts may be considered as new antifungal agents and biofilm inhibiting agents for the pharmaceutical and agro-food field.

Molybdenum oxide nanotube caps decorated with ultrafine Ag nanoparticles: Synthesis and antimicrobial activity

In the contemporary era, microorganisms, spanning bacteria and viruses, are increasingly acknowledged as emerging contaminants in the environment, presenting significant risks to public health. Nevertheless, conventional methods for disinfecting these microorganisms are often ineffective. Additionally, they come with disadvantages such as high energy usage, negative environmental consequences, increased expenses, and the generation of harmful byproducts. The development of next-generation antifungal and antibacterial agents is dependent on newly synthesized nanomaterials with inherent antimicrobial behavior. In this study, we report an arc-discharge method to synthesize MoOx nanosheets and microbelts, followed by decorating them with ultrafine Ag nanoparticles (NPs). Scanning and transmission electron microscopies show that Ag NPs formation on the Molybdenum oxide nanostructures rolls them into nanotube caps (NTCs), revealing inner and outer diameters of approximately 19.8 nm and 105.5 nm, respectively. Additionally, the Ag NPs are ultrafine, with sizes in the range of 5-8 nm. Results show that the prepared NTCs exhibit dose-dependent sensitivity to both planktonic and biofilm cells of Escherichia coli and Candida albicans. The anti-biofilm activity in terms of biofilm inhibition ranged from 19.7 to 77.2% and 11.3-82.3%, while removal of more than 70% and 90% of preformed biofilms was achieved for E. coli and C. albicans, respectively, showing good potential for antimicrobial coating. Initial MoOx exhibits positive potential, while Ag-decorated Molybdenum oxide NTCs show dual potential effects (positive for Molybdenum oxide NTCs and negative for Ag NPs. Molybdenum oxide NTCs, with their strong positive potential, efficiently attract microbes due to their negatively charged cell surfaces, facilitating the antimicrobial effect of Ag NPs, leading to cell damage and death. These findings suggest that the synthesized NPs could serve as a suitable coating for biomedical applications.

Synergistic effect of chlorhexidine and azoles on candida biofilm on titanium surface

BACKGROUND

Candida infections of orthopedic implants are one of the most detrimental orthopedic implant-related complications with unsuccessful treatment and a poor prognosis. Most orthopedic Candida infections form biofilms and have resistance to the commonly used antifungal agents. This study aimed to develop a novel combination of normally prescribed drugs against Candida biofilm on orthopedic implants.

METHODS

We cultured 26 clinical isolates of Candida strains to form biofilm without titanium sheets or on titanium sheets, which are the most commonly used materials for permanent or orthopedic implants. The checkerboard method was used to evaluate the synergistic effects of chlorhexidine (CHL) and azoles on these Candida biofilms. For the evaluation of synergistic effects, we constructed the cell viability assay by fluorescence staining and CFU reduction hot map of Candida.

RESULTS

Twenty-six clinical isolates of Candida strains formed biofilm in 96-well plates without titanium sheets, and we selected 9 of them to form biofilm on titanium sheets in 24-well plates. In Candida biofilm formed in 96-wells, the synergistic rates of CHL with fluconazole, itraconazole, and voriconazole were 61% (16/26), 65% (17/26), and 23% (6/26), respectively. When compared to the blank control group, CHL monotherapy significantly inhibited biofilm formation on titanium sheets (P < 0.05). We demonstrated 100% synergistic rates of the CHL and fluconazole combination against Candida biofilm formation on titanium sheets, and the minimum inhibitory concentration of CHL and FLU decreased four- to eight-fold.

CONCLUSIONS

We concluded that CHL combined with azoles inhibited the Candida biofilm formation 96-wells or on titanium sheets and has the potential to control the infections of orthopedic implants.

Streptomyces: a natural source of anti-Candida agents

Introduction. There is an urgent need to source new compounds that can combat the current threat of serious infection caused by Candida spp. and contend with the problem of antimicrobial resistance.

Gap. A synthesis of the evidence available from the current literature is needed to identify promising antifungal chemotherapeutics.

Aim. To highlight anti-Candida compounds derived from Streptomyces spp. (a well-known source of antimicrobial compounds) that could translate to potential candidates for future clinical practice.

Methodology. A comprehensive review was conducted across three scientific literature databases spanning a 13-year period.

Results. We identified 151 compounds with anti-Candida activity. Amongst these, 40 were reported with very strong inhibitory activity, having minimum inhibitory concentrations (MICs) against Candida spp. of <3.5 µg ml−1, 66 compounds were considered strong inhibitors and 45 compounds exhibited moderate inhibitory potential. From an analysis of the MICs, we deduced that the actinomycin-like compounds RSP01 and RSP02 were probably the most promising anti-Candida compounds. Other antifungals of note included filipin-like compounds, which demonstrated superior inhibition to amphotericin B and activity against Candida glabrata and Candida krusei, and bafilomycin derivatives, which had substantial inhibition against Candida parapsilosis.

Conclusion. It is essential to recognize the limitations inherent in the quest for new antifungals, which encompass toxicity, in vivo effectiveness and constraints associated with limited data access. However, further investigation through in-depth study and emerging technologies is of paramount importance, given that there are still many more compounds to discover. This review highlights the importance of antifungal compounds derived from Streptomyces , which demonstrate robust inhibition, and, in many cases, low toxicity, making them promising candidates for the development of novel antifungal agents.

Medicinal benefits, biological, and nanoencapsulation functions of riboflavin with its toxicity profile: A narrative review

Riboflavin is a precursor of the essential coenzymes flavin mononucleotide and flavin adenine dinucleotide. Both possess antioxidant properties and are involved in oxidation-reduction reactions, which have a significant impact on energy metabolism. Also, the coenzymes participate in metabolism of pyridoxine, niacin, folate, and iron. Humans must obtain riboflavin through their daily diet because of the lack of programmed enzymatic machineries for de novo riboflavin synthesis. Because of its physiological nature and fast elimination from the human body when in excess, riboflavin consumed is unlikely to induce any negative effects or develop toxicity in humans. The use of riboflavin in pharmaceutical and clinical contexts has been previously explored, including for preventing and treating oxidative stress and reperfusion oxidative damage, creating synergistic compounds to mitigate colorectal cancer, modulating blood pressure, improving diabetes mellitus comorbidities, as well as neuroprotective agents and potent photosensitizer in killing bloodborne pathogens. Thus, the goal of this review is to provide a comprehensive understanding of riboflavin's biological applications in medicine, key considerations of riboflavin safety and toxicity, and a brief overview on the nanoencapsulation of riboflavin for various functions including the treatment of a range of diseases, photodynamic therapy, and cellular imaging.

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

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

A potential alternative to fungicides using actives-free (meth)acrylate polymers for protection of wheat crops from fungal attachment and infection

Fungicidal compounds are actives widely used for crop protection from fungal infection, but they can also kill beneficial organisms, enter the food chain and promote resistant pathogen strains from overuse. Here we report the first field crop trial of homopolymer materials that prevent fungal attachment, showing successful crop protection via an actives-free approach. In the trial, formulations containing two candidate polymers were applied to young wheat plants that were subject to natural infection with the wheat pathogen Zymoseptoria tritici. A formulation containing one of the candidate polymers, poly(di(ethylene glycol) ethyl ether acrylate) (abbreviated DEGEEA), produced a significant reduction (26%) in infection of the crop by Z. tritici, delivering protection against fungal infection that compared favourably with three different commercially established fungicide programmes tested in parallel. Furthermore, the sprayed polymers did not negatively affect wheat growth. The two lead polymer candidates were initially identified by bio-performance testing using in vitro microplate- and leaf-based assays and were taken forward successfully into a programme to optimize and scale-up their synthesis and compound them into a spray formulation. Therefore, the positive field trial outcome has also established the validity of the smaller-scale, laboratory-based bioassay data and scale-up methodologies used. Because fungal attachment to plant surfaces is a first step in many crop infections, this non-eluting polymer: (i) now offers significant potential to deliver protection against fungal attack, while (ii) addressing the fourth and aligning with the eleventh principles of green chemistry by using chemical products designed to preserve efficacy of function while reducing toxicity. A future focus should be to develop the material properties for this and other applications including other fungal pathogens.

Contribution of N-Linked Mannosylation Pathway to Candida parapsilosis and Candida tropicalis Biofilm Formation

Background

Mycoses are a growing threat to human health, and systemic candidiasis caused by Candida parapsilosis and Candida tropicalis is frequent in immunocompromised patients. Biofilm formation is a virulence factor found in these organisms, as sessile cells adhere to surfaces, the stratification and production of extracellular matrix provides protection and resistance to antifungal drugs. Previous evidence indicated that the N-linked mannosylation pathway is relevant to C. albicans biofilms, but its contribution to other species remains unknown.

Methods

C. parapsilosis and C. tropicalis och1∆ mutants, which have a disrupted N-linked mannosylation pathway, were used to form biofilms. In addition, wild-type and mutant cells were also treated to remove N-linked mannans or block this pathway. Biofilms were analyzed by quantifying the included fungal biomass, and extracellular matrix components. Moreover, gene expression and secreted hydrolytic enzymes were also quantified in these biofilms.

Results

The och1∆ mutants showed a reduced ability to form biofilms in both fungal species when compared to the wild-type and control strains. This observation was confirmed by trimming N-linked mannans from walls or blocking the pathway with tunicamycin B. According to this observation, mutant, and treated cells showed an altered composition of the extracellular matrix and increased susceptibility to antifungal drugs when compared to control or untreated cells. The gene expression of secreted virulence factors, such as aspartyl proteinases and phospholipases, was normal in all the tested cells but the secreted activity was reduced, suggesting a defect in the secretory pathway, which was later confirmed by treating cells with brefeldin A.

Conclusion

Proper N-linked mannosylation is required for biofilm formation in both C. parapsilosis and C. tropicalis. Disruption of this posttranslational modification affected the secretory pathway, offering a link between glycosylation and biofilm formation.

Cyclic strain of poly (methyl methacrylate) surfaces triggered the pathogenicity of Candida albicans

Candida albicans is an opportunistic yeast and the primary etiological factor in oral candidiasis and denture stomatitis. The pathogenesis of C. albicans could be triggered by several variables, including environmental, nutritional, and biomaterial surface cues. Specifically, biomaterial interactions are driven by different surface properties, including wettability, stiffness, and roughness. Dental biomaterials experience repetitive (cyclic) stresses from chewing and biomechanical movements. Pathogenic biofilms are formed over these biomaterial surfaces under cyclic strain. This study investigated the effect of the cyclic strain (deformation) of biomaterial surfaces on the virulence of Candida albicans. Candida biofilms were grown over Poly (methyl methacrylate) (PMMA) surfaces subjected to static (no strain) and cyclic strain with different levels (ε˜x=0.1 and 0.2%). To evaluate the biomaterial-biofilm interactions, the biofilm characteristics, yeast-to-hyphae transition, and the expression of virulent genes were measured. Results showed the biofilm biomass and metabolic activity to be significantly higher when Candida adhered to surfaces subjected to cyclic strain compared to static surfaces. Examination of the yeast-to-hyphae transition showed pseudo-hyphae cells (pathogenic) in cyclically strained biomaterial surfaces, whereas static surfaces showed spherical yeast cells (commensal). RNA sequencing was used to determine and compare the transcriptome profiles of cyclically strained and static surfaces. Genes and transcription factors associated with cell adhesion (CSH1, PGA10, and RBT5), biofilm formation (EFG1), and secretion of extracellular matrix (ECM) (CRH1, ADH5, GCA1, and GCA2) were significantly upregulated in the cyclically strained biomaterial surfaces compared to static ones. Genes and transcription factors associated with virulence (UME6 and HGC1) and the secretion of extracellular enzymes (LIP, PLB, and SAP families) were also significantly upregulated in the cyclically strained biomaterial surfaces compared to static. For the first time, this study reveals a biomaterial surface factor triggering the pathogenesis of Candida albicans, which is essential for understanding, controlling, and preventing oral infections. STATEMENT OF SIGNIFICANCE: Fungal infections produced by Candida albicans are a significant contributor to various health conditions. Candida becomes pathogenic when certain environmental conditions change, including temperature, pH, nutrients, and CO2 levels. In addition, surface properties, including wettability, stiffness, and roughness, drive the interactions between Candida and biomaterials. Clinically, Candida adheres to biomaterials that are under repetitive deformation due to body movements. In this work, we revealed that when Candida adhered to biomaterial surfaces subjected to repetitive deformation, the microorganism becomes pathogenic by increasing the formation of biofilms and the expression of virulent factors related to hyphae formation and secretion of enzymes. Findings from this work could aid the development of new strategies for treating fungal infections in medical devices or implanted biomaterials.