Facilitators of adaptation and antifungal resistance mechanisms in clinically relevant fungi

Strategies of Pharmacological Repositioning for the Treatment of Medically Relevant Mycoses

Fungal infections represent a worldwide concern for public health, due to their prevalence and significant increase in cases each year. Among the most frequent mycoses are those caused by members of the genera Candida, Cryptococcus, Aspergillus, Histoplasma, Pneumocystis, Mucor, and Sporothrix, which have been treated for years with conventional antifungal drugs, such as flucytosine, azoles, polyenes, and echinocandins. However, these microorganisms have acquired the ability to evade the mechanisms of action of these drugs, thus hindering their treatment. Among the most common evasion mechanisms are alterations in sterol biosynthesis, modifications of drug transport through the cell wall and membrane, alterations of drug targets, phenotypic plasticity, horizontal gene transfer, and chromosomal aneuploidies. Taking into account these problems, some research groups have sought new therapeutic alternatives based on drug repositioning. Through repositioning, it is possible to use existing pharmacological compounds for which their mechanism of action is already established for other diseases, and thus exploit their potential antifungal activity. The advantage offered by these drugs is that they may be less prone to resistance. In this article, a comprehensive review was carried out to highlight the most relevant repositioning drugs to treat fungal infections. These include antibiotics, antivirals, anthelmintics, statins, and anti-inflammatory drugs.

Safety and efficacy of new generation azole antifungals in the management of recalcitrant superficial fungal infections and onychomycosis

INTRODUCTION

Terbinafine is considered the gold standard for treating skin fungal infections and onychomycosis. However, recent reports suggest that dermatophytes are developing resistance to terbinafine and the other traditional antifungal agents, itraconazole and fluconazole. When there is resistance to terbinafine, itraconazole or fluconazole, or when these agents cannot used, for example, due to potential drug interactions with the patient's current medications, clinicians may need to consider off-label use of new generation azoles, such as voriconazole, posaconazole, fosravuconazole, or oteseconazole. It is essential to emphasize that we do not advocate the use of newer generation azoles unless traditional agents such as terbinafine, itraconazole, or fluconazole have been thoroughly evaluated as first-line therapies.

AREAS COVERED

This article reviews the clinical evidence, safety, dosage regimens, pharmacokinetics, and management algorithm of new-generation azole antifungals.

EXPERT OPINION

Antifungal stewardship should be the top priority when prescribing new-generation azoles. First-line antifungal therapy is terbinafine and itraconazole. Fluconazole is a consideration but is generally less effective and its use may be off-label in many countries. For difficult-to-treat skin fungal infections and onychomycosis, that have failed terbinafine, itraconazole and fluconazole, we propose consideration of off-label voriconazole or posaconazole.

Drug repurposing for fungal infections

The rise of multidrug-resistant bacteria is a well-recognized threat to world health, necessitating the implementation of effective treatments. This issue has been identified as a top priority on the global agenda by the World Health Organization. Certain strains, such as Candida glabrata, Candida krusei, Candida lusitaniae, Candida auris, select cryptococcal species, and opportunistic Aspergillus or Fusarium species, have significant intrinsic resistance to numerous antifungal medicines. This inherent resistance and subsequent suboptimal clinical outcomes underscore the critical imperative for enhanced therapeutic alternatives and management protocols. The challenge of effectively treating fungal infections, compounded by the protracted timelines involved in developing novel drugs, underscores the pressing need to explore alternative therapeutic avenues. Among these, drug repurposing emerges as a particularly promising and expeditious solution, providing cost-effective solutions and safety benefits. In the fight against life-threatening resistant fungal infections, the idea of repurposing existing medications has encouraged research into both established and new compounds as a last-resort therapy. This chapter seeks to provide a comprehensive overview of contemporary antifungal drugs, as well as their key resistance mechanisms. Additionally, it seeks to provide insight into the antimicrobial properties of non-traditional drugs, thereby offering a holistic perspective on the evolving landscape of antifungal therapeutics.

Computer-made peptide RQ18 acts as a dual antifungal and antibiofilm peptide though membrane-associated mechanisms of action

The spread of fungi resistant to conventional drugs has become a threatening problem. In this context, antimicrobial peptides (AMPs) have been considered as one of the main alternatives for controlling fungal infections. Here, we report the antifungal and antibiofilm activity and some clues about peptide RQ18's mechanism of action against Candida and Cryptococcus. This peptide inhibited yeast growth from 2.5 μM and killed all Candida tropicalis cells within 2 h incubation. Moreover, it showed a synergistic effect with antifungal agent the amphotericin b. RQ18 reduced biofilm formation and promoted C. tropicalis mature biofilms eradication. RQ18's mechanism of action involves fungal cell membrane damage, which was confirmed by the results of RQ18 in the presence of free ergosterol in the medium and fluorescence microscopy by Sytox green. No toxic effects were observed in murine macrophage cell lines and Galleria mellonella larvae, suggesting fungal target selectivity. Therefore, peptide RQ18 represents a promising strategy as a dual antifungal and antibiofilm agent that contributes to infection control without damaging mammalian cells.

Nanoparticles assisted intra and transdermic delivery of antifungal ointment: an updated review

This review paper highlights the trans-dermic delivery of nanoparticles (NPs) based antifungal ointments with the help of nanotechnology. It also describes the novel trans-dermal approach utilizing various nanoparticles which enables an efficient delivery to the target site. This current review gives an overview about past research and developments as well as the current nanoparticle-based ointments. This review also presents data regarding types, causes of infection, and different pathogens within their infection site. It also gives information about antifungal ointments with their activity and side effects of antifungal medicines. Additionally, this review also focuses on the future aspects of the topical administration of nanoparticle-based antifungal ointments. These nanoparticles can encapsulate multiple antifungal drugs as a combination therapy targeting different aspects of fungal infection. Nanoparticles can be designed in such a way that they can specifically target fungal cells and do not affect healthy cells. Nanoparticle based antifungal ointments exhibit outstanding potential to treat fungal diseases. As further research and advancements evolve in nanotechnology, we expect more development of nanoparticle-based antifungal formulations shortly. This paper discusses all the past and future applications, recent trends, and developments in the various field and also shows its bright prospective in the upcoming years.

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.

A promising synthetic citric crosslinked β-cyclodextrin derivative for antifungal drugs: Solubilization, cytotoxicity, and antifungal activity

Effective antifungal therapy for the treatment of fungal keratitis requires a high drug concentration at the corneal surface. However, the use of natural β-cyclodextrin (βCD) in the preparation of aqueous eye drop formulations for treating fungal keratitis is limited by its low aqueous solubility. Here, we synthesized water-soluble anionic βCD derivatives capable of forming water-soluble complexes and evaluated the solubility, cytotoxicity, and antifungal efficacy of drug prepared using the βCD derivative. To achieve this, a citric acid crosslinked βCD (polyCTR-βCD) was successfully synthesized, and the aqueous solubilities of selected antifungal drugs, including voriconazole, miconazole (MCZ), itraconazole, and amphotericin B, in polyCTR-βCD and analogous βCD solutions were evaluated. Among the drugs tested, complexation of MCZ with polyCTR-βCD (MCZ/polyCTR-βCD) increased MCZ aqueous solubility by 95-fold compared with that of MCZ/βCD. The inclusion complex formation of MCZ/βCD and MCZ/polyCTR-βCD was confirmed by spectroscopic techniques. Additionally, the nanoaggregates of saturated MCZ/polyCTR-βCD and MCZ/βCD solutions were observed using dynamic light scattering and transmission electron microscopy. Moreover, MCZ/polyCTR-βCD solution exhibited good mucoadhesion, sustained drug release, and high drug permeation of porcine cornea ex vivo. Hen's Egg test-chorioallantoic membrane assay and cell viability study using Statens Seruminstitut Rabbit Cornea cell line showed that both MCZ/polyCTR-βCD and MCZ/βCD exhibited no sign of irritation and non-toxic to cell line. Additionally, antifungal activity evaluation demonstrated that all isolated fungi, including Candida albicans, Aspergillus flavus, and Fusarium solani, were susceptible to MCZ/polyCTR-βCD. Overall, the results showed that polyCTR-βCD could be a promising nanocarrier for the ocular delivery of MCZ.

Bovine Lactoferrin-Loaded Plasmonic Magnetoliposomes for Antifungal Therapeutic Applications

Bovine lactoferrin (bLf) is a milk-derived protein that exhibits potent broad-spectrum antifungal activity against multiple fungi. bLf is susceptible to degradation, while some of its properties depend on the tertiary structure. So, the encapsulation of bLf in stimuli-responsive therapeutic formulations provides an added value to enhance its biological activities. Plasmonic magnetoliposomes (PMLs) arise as promising nanocarriers for dual hyperthermia (magneto-photothermia) and local chemotherapy, since the combination of magnetic and gold nanoparticles (NPs) in a single nanosystem (multifunctional liposomes) enables the targeting and controlled release of loaded drugs. In this work, plasmonic magnetoliposomes (PMLs) containing manganese ferrite nanoparticles (28 nm size) and gold nanoparticles (5-7.5 nm size), functionalized with 11-mercaptoundecanoic acid or octadecanethiol, were prepared and loaded with bLf. The NPs' optical, magnetic and structural properties were measured via UV/vis/NIR absorption spectroscopy, SQUID and TEM, respectively. The Specific Absorption Rate (SAR) was calculated to assess the capabilities for magnetic and photothermal hyperthermia. Finally, the antifungal potential of bLf-loaded PMLs and their mechanism of internalization were assessed in Saccharomyces cerevisiae by counting the colony forming units and using fluorescence microscopy. The results demonstrate that PMLs are mainly internalized through an energy- and temperature-dependent endocytic process, though the contribution of a diffusion component cannot be discarded. Most notably, only bLf-loaded plasmonic magnetoliposomes display cytotoxicity with an efficiency similar to free bLf, attesting their promising potential for bLf delivery in the context of antifungal therapeutic interventions.

Nanotechnology-Based Strategies to Combat Multidrug-Resistant Candida auris Infections

An emerging multidrug-resistant pathogenic yeast called Candida auris has a high potential to spread quickly among hospitalized patients and immunodeficient patients causing nosocomial outbreaks. It has the potential to cause pandemic outbreaks in about 45 nations with high mortality rates. Additionally, the fungus has become resistant to decontamination techniques and can survive for weeks in a hospital environment. Nanoparticles might be a good substitute to treat illnesses brought on by this newly discovered pathogen. Nanoparticles have become a trend and hot topic in recent years to combat this fatal fungus. This review gives a general insight into the epidemiology of C. auris and infection. It discusses the current conventional therapy and mechanism of resistance development. Furthermore, it focuses on nanoparticles, their different types, and up-to-date trials to evaluate the promising efficacy of nanoparticles with respect to C. auris.

The Transcriptome Response to Azole Compounds in Aspergillus fumigatus Shows Differential Gene Expression across Pathways Essential for Azole Resistance and Cell Survival

The opportunistic pathogen Aspergillus fumigatus is found on all continents and thrives in soil and agricultural environments. Its ability to readily adapt to novel environments and to produce billions of spores led to the spread of azole-resistant A. fumigatus across the globe, posing a threat to many immunocompromised patients, including critically ill patients with severe influenza or COVID-19. In our study, we sought to compare the adaptational response to azoles from A. fumigatus isolates that differ in azole susceptibility and genetic background. To gain more insight into how short-term adaptation to stressful azole compounds is managed through gene expression, we conducted an RNA-sequencing study on the response of A. fumigatus to itraconazole and the newest clinically approved azole, isavuconazole. We observed many similarities in ergosterol biosynthesis up-regulation across isolates, with the exception of the pan-azole-resistant isolate, which showed very little differential regulation in comparison to other isolates. Additionally, we found differential regulation of membrane efflux transporters, secondary metabolites, iron metabolism, and various stress response and cell signaling mechanisms.

Improvement of Akanthomyces lecanii resistance to tebuconazole through UV-C radiation and selective pressure on microbial evolution and growth arenas

Tebuconazole (TEB) is a fungicide widely used in agriculture; however, its constant application has increased the emergence of resistant plant pathogenic fungal strains and reduced the effectiveness of fungi as biological control agents; for instance, the entomopathogenic and hyperparasitic fungus Akanthomyces lecanii, suitable for simultaneous biological control of insect pest and plant pathogenic fungi, is highly sensitive to fungicides. We carried out the induction of resistance to TEB in two wild type strains of A. lecanii by UV radiation and selective pressure in increasing fungicide gradients using a modified Microbial Evolution and Growth Arena (MEGA), to produce A. lecanii strains that can be used as biological control agent in the presence of tebuconazole. Nine UV-induced and three naturally adapted A. lecanii strains were resistant to TEB at the agriculturally recommended dose, and three irradiated strains were resistant to TEB concentration ten times higher; moreover, growth, sporulation rates, production of hydrolytic enzymes, and virulence against the hemipteran Coccus viridis, a major pest of coffee crops, were not affected in the TEB-resistant strains. These A. lecanii TEB-resistant strains would have a greater opportunity to develop and to establish themselves in fields where the fungicide is present and can be used in a combined biological-chemical strategy to improve insect and plant pathogenic fungal control in agriculture. Also, the selective pressure through modified MEGA plate methodology can be used for the adaptation of entomopathogenic filamentous fungi to withstand other chemical or abiotic stresses that limits its effectiveness for pest control.

Using inorganic nanoparticles to fight fungal infections in the antimicrobial resistant era

Fungal infections pose a serious threat to human health and livelihoods. The number and variety of clinically approved antifungal drugs is very limited, and the emergence and rapid spread of resistance to these drugs means the impact of fungal infections will increase in the future unless alternatives are found. Despite the significance and major challenges associated with fungal infections, this topic receives significantly less attention than bacterial infections. A major challenge in the development of fungi-specific drugs is that both fungi and mammalian cells are eukaryotic and have significant overlap in their cellular machinery. This lack of fungi-specific drug targets makes human cells vulnerable to toxic side effects from many antifungal agents. Furthermore, antifungal drug resistance necessitates higher doses of the drugs, leading to significant human toxicity. There is an urgent need for new antifungal agents, specifically those that can limit the emergence of new resistant species. Non-drug nanomaterials have primarily been explored as antibacterial agents in recent years; however, they are also a promising source of new antifungal candidates. Thus, this article reviews current research on the use of inorganic nanoparticles as antifungal agents. We also highlight challenges facing antifungal nanoparticles and discuss possible future research opportunities in this field. STATEMENT OF SIGNIFICANCE: Fungal infections pose a growing threat to human health and livelihood. The rapid spread of resistance to current antifungal drugs has led to an urgent need to develop alternative antifungals. Nanoparticles have many properties that could make them useful antimycotic agents. To the authors' knowledge, there is no published review so far that has comprehensively summarized the current development status of antifungal inorganic nanomaterials, so we decided to fill this gap. In this review, we discussed the state-of-the-art research on antifungal inorganic nanoparticles including metal, metal oxide, transition-metal dichalcogenides, and inorganic non-metallic particle systems. Future directions for the design of inorganic nanoparticles with higher antifungal efficacy and lower toxicity are described as a guide for further development in this important area.

Existing and emerging therapies for the treatment of invasive candidiasis and candidemia

INTRODUCTION

Invasive candidiasis or candidemia is a severe infection affecting more than 250,000 people worldwide every year. It is present in up to 16% of ICU patients. The prognosis of these infections is unfavorable, with global death estimated around 50,000 per year, which corresponds to up to 40% depending on patient severity and comorbidities. Therapeutic failure is not rare due to the emergence of multiresistant strains and of new species poorly responsive to current therapies like Candida auris.

AREAS COVERED

We first review the positioning of antifungal drugs used to treat candidiasis, namely polyenes, azoles, echinocandins and pyrimidine analogues. We then discuss the progresses brought by new formulations, new derivatives within these classes, compounds acting on new targets or repurposed drugs in terms of pharmacokinetic profile, spectrum of activity, potency, safety or risk of drug-drug interactions.

EXPERT OPINION

While new formulations (amphotericin B cochleate) improve oral bioavailability of the corresponding drugs, new azoles or echinocandins offer higher potency including against strains resistant to former generations of drugs. Repurposed drugs show synergism with current therapies in vitro. Results from ongoing and future clinical trials will be decisive to establish the interest for these drugs in our arsenal.

A Current Overview of Cyclodextrin-Based Nanocarriers for Enhanced Antifungal Delivery

Fungal infections are an extremely serious health problem, particularly in patients with compromised immune systems. Most antifungal agents have low aqueous solubility, which may hamper their bioavailability. Their complexation with cyclodextrins (CDs) could increase the solubility of antifungals, facilitating their antifungal efficacy. Nanoparticulate systems are promising carriers for antifungal delivery due to their ability to overcome the drawbacks of conventional dosage forms. CD-based nanocarriers could form beneficial combinations of CDs and nanoparticulate platforms. These systems have synergistic or additive effects regarding improved drug loading, enhanced chemical stability, and enhanced drug permeation through membranes, thereby increasing the bioavailability of drugs. Here, an application of CD in antifungal drug formulations is reviewed. CD-based nanocarriers, such as nanoparticles, liposomes, nanoemulsions, nanofibers, and in situ gels, enhancing antifungal activity in a controlled-release manner and possessing good toxicological profiles, are described. Additionally, the examples of current, updated CD-based nanocarriers loaded with antifungal drugs for delivery by various routes of administration are discussed and summarized.

Molecular Mechanisms of Antifungal Resistance in Mucormycosis

Mucormycosis is one among the life-threatening fungal infections with high morbidity and mortality. It is an uncommon and rare infection targeting people with altered immunity. This lethal infection induced by fungi belonging to the Mucorales family is very progressive in nature. The incidence has increased in recent decades owing to the rise in immunocompromised patients. Disease management involves a multimodal strategy including early administration of drugs and surgical removal of infected tissues. Among the antifungals, azoles and amphotericin B remain the gold standard drugs of choice for initial treatment. The order Mucorales are developing a high level of resistance to the available systemic antifungal drugs, and the efficacy still remains below par. Deciphering the molecular mechanisms behind the antifungal resistance in Mucormycosis would add vital information to our available antifungal armamentarium and design novel therapies. Therefore, in this review, we have discussed the mechanisms behind Mucormycosis antifungal resistance. Moreover, this review also highlights the basic mechanisms of action of antifungal drugs and the resistance landscape which is expected to augment future treatment strategies.

In Vitro Activity of Essential Oils Distilled from Colombian Plants against Candidaauris and Other Candida Species with Different Antifungal Susceptibility Profiles

Multi-drug resistant species such as Candida auris are a global health threat. This scenario has highlighted the need to search for antifungal alternatives. Essential oils (EOs), or some of their major compounds, could be a source of new antifungal molecules. The aim of this study was to evaluate the in vitro activity of EOs and some terpenes against C. auris and other Candida spp. The eleven EOs evaluated were obtained by hydro-distillation from different Colombian plants and the terpenes were purchased. EO chemical compositions were obtained by gas chromatography/mass spectrometry (GC/MS). Antifungal activity was evaluated following the CLSI standard M27, 4th Edition. Cytotoxicity was tested on the HaCaT cell line and fungal growth kinetics were tested by time–kill assays. Candida spp. showed different susceptibility to antifungals and the activity of EOs and terpenes was strain-dependent. The Lippia origanoides (thymol + p-cymene) chemotype EO, thymol, carvacrol, and limonene were the most active, mainly against drug-resistant strains. The most active EOs and terpenes were also slightly cytotoxic on the HaCaT cells. The findings of this study suggest that some EOs and commercial terpenes can be a source for the development of new anti-Candida products and aid the identification of new antifungal targets or action mechanisms.

Bioactive Antimicrobial Peptides: A New Weapon to Counteract Zoonosis

Zoonoses have recently become the center of attention of the general population and scientific community. Notably, more than 30 new human pathogens have been identified in the last 30 years, 75% of which can be classified as zoonosis. The complete eradication of such types of infections is far out of reach, considering the limited understanding of animal determinants in zoonoses and their causes of emergence. Therefore, efforts must be doubled in examining the spread, persistence, and pathogenicity of zoonosis and studying possible clinical interventions and antimicrobial drug development. The search for antimicrobial bioactive compounds has assumed great emphasis, considering the emergence of multi-drug-resistant microorganisms. Among the biomolecules of emerging scientific interest are antimicrobial peptides (AMPs), potent biomolecules that can potentially act as important weapons against infectious diseases. Moreover, synthetic AMPs are easily tailored (bioinformatically) to target specific features of the pathogens to hijack, inducing no or very low resistance. Although very promising, previous studies on SAMPs' efficacy are still at their early stages. Indeed, further studies and better characterization on their mechanism of action with in vitro and in vivo assays are needed so as to proceed to their clinical application on human beings.

Post-Translational Modifications of PCNA: Guiding for the Best DNA Damage Tolerance Choice

The sliding clamp PCNA is a multifunctional homotrimer mainly linked to DNA replication. During this process, cells must ensure an accurate and complete genome replication when constantly challenged by the presence of DNA lesions. Post-translational modifications of PCNA play a crucial role in channeling DNA damage tolerance (DDT) and repair mechanisms to bypass unrepaired lesions and promote optimal fork replication restart. PCNA ubiquitination processes trigger the following two main DDT sub-pathways: Rad6/Rad18-dependent PCNA monoubiquitination and Ubc13-Mms2/Rad5-mediated PCNA polyubiquitination, promoting error-prone translation synthesis (TLS) or error-free template switch (TS) pathways, respectively. However, the fork protection mechanism leading to TS during fork reversal is still poorly understood. In contrast, PCNA sumoylation impedes the homologous recombination (HR)-mediated salvage recombination (SR) repair pathway. Focusing on Saccharomyces cerevisiae budding yeast, we summarized PCNA related-DDT and repair mechanisms that coordinately sustain genome stability and cell survival. In addition, we compared PCNA sequences from various fungal pathogens, considering recent advances in structural features. Importantly, the identification of PCNA epitopes may lead to potential fungal targets for antifungal drug development.

Fungal infections: Pathogenesis, antifungals and alternate treatment approaches

Increasing incidence of fungal infections of recent times requires immediate intervention. Fungal infections are seldom construed at initial stages that intensify the severity of infections and complicate the treatment procedures. Fungal pathogens employ various mechanisms to evade the host immune system and to progress the severity of infections. For the treatment of diverse superficial and systemic infections, antifungal drugs from the available repertoire are administered. However, well documented evidence of fungal resistance to most of the antifungal drugs hampers disease control and poses challenges in antifungal therapy. Several physiological adaptations and genetic mutations followed by their selection in presence of antifungal agents drive the resistance development in fungi. The availability of limited antifungal arsenal, emergence of resistance and biofilm-conferred resistance drives the need for development of novel drugs and alternate approaches for the better treatment outcome against mycoses. This graphical review explicitly shed light on various fungal infections and causative organisms, pathogenesis, different antifungal drugs and resistance mechanisms including host immune response and evasion strategies. Here, we have highlighted recent developments on novel antifungal agents and other alternate approaches for fighting against fungal infections.

Mechanical and antimicrobial effects of riboflavin-mediated photosensitization of in vitro C. albicans formed on polymethyl methacrylate resin

PURPOSE

This study assessed the potential of riboflavin-mediated photodynamic therapy (RF-PDT) against Candida albicans (C. albicans) and compared the effects of RF-PDT with other therapeutic modalities in terms of mechanical and surface characteristics of acrylic denture base material.

MATERIALS AND METHODS

Molds (10 × 10 × 2 mm) of acrylic resin specimens were prepared and underwent artificial ageing. C. albicans were grown aerobically over the specimens and divided into four groups (n = 10/group); Group-I: no decontamination; Group-II: nystatin suspension; Group-III: riboflavin 0.1% in darkness, Group-IV: blue LED light only, and Group-V: riboflavin 0.1% for 10 minutes (pre-irradiation time) and photoactivated by the blue LED light (light dose). Fungal viability was assessed using MTT assay and characterized using scanning electron microscopy and confocal laser microscopy (CLSM). Treated specimens were subjected to surface roughness (R_a), flexural strength (FS), and flexural modulus (FM).

RESULTS

Group-I showed the highest C. albicans viability followed by Group-III. Nystatin group (Group-II) showed ∼50% of the viability while RF-PDT showed the least C. albicans viability among the four groups (p<0.05). On SEM, specimens treated with Group-IV and V showed almost clear and free from C. albicans that was evidenced on CLSM. Post-treated specimens and storage after 72 h revealed that FS was significantly higher for RF-PDT group as compared to any other group (>105.82 MPa) (p<0.05). The FM and Ra showed statistically no significant difference between the groups (p>0.05).

CONCLUSION

RF-PDT showed the highest anti-fungal capacity against C. albicans over acrylic denture surface without any surface deterioration.

Preliminary Characterization of NP339, a Novel Polyarginine Peptide with Broad Antifungal Activity

Fungi cause disease in nearly one billion individuals worldwide. Only three classes of antifungal agents are currently available in mainstream clinical use. Emerging and drug-resistant fungi, toxicity, and drug-drug interactions compromise their efficacy and applicability. Consequently, new and improved antifungal therapies are urgently needed. In response to that need, we have developed NP339, a 2-kDa polyarginine peptide that is active against pathogenic fungi from the genera Candida, Aspergillus, and Cryptococcus, as well as others. NP339 was designed based on endogenous cationic human defense peptides, which are constituents of the cornerstone of immune defense against pathogenic microbes. NP339 specifically targets the fungal cell membrane through a charge-charge-initiated membrane interaction and therefore possesses a differentiated safety and toxicity profile to existing antifungal classes. NP339 is rapidly fungicidal and does not elicit resistance in target fungi upon extensive passaging in vitro. Preliminary analyses in murine models indicate scope for therapeutic application of NP339 against a range of systemic and mucocutaneous fungal infections. Collectively, these data indicate that NP339 can be developed into a highly differentiated, first-in-class antifungal candidate for poorly served invasive and other serious fungal diseases.

A Simple Antifungal assay for Testing Actinomycetes and Other Microbial Extracts

Antifungal assay in vitro is a useful tool for the characterization of biological activity of microbial extracts. Here we describe a simple in vitro test at two final extract concentrations that allows long-term storage of the plates containing dry extracts before using. The assay protocol is described for two fungal strains, a unicellular yeast, with clinical interest (Candida albicans), and a sporulated and phytopathogenic filamentous fungus (Botrytis cinerea). They could serve as models for adapting other filamentous/yeast-like fungi.Plates are prepared by placing 100 and 10 μg, respectively, of the organic extracts in microtiter 96-well plates, where the test will be performed. The assay develops by adding 200 μL of a spore suspension 10⁴ spores/mL for B. cinerea and 10⁶ cells/mL for C. albicans in Sabouraud medium.After the incubation of the plates at 25 °C, for 2 days for C. albicans and 5 days for B. cinerea , the growth of the fungal targets is evaluated in a plate reader for unicellular yeast , or visually under the microscope for filamentous fungi. If visually evaluated, observed growth can be assigned to different categories by comparison with growth control and inhibition control. Inhibition effect on C. albicans at eight concentrations of amphotericin B (8-4-2-1-0.5-0.25-0.125-0.00625 μg/mL) or B. cinerea exposed of eight concentrations of iprodione (100-50-10-5-1-0.5-0.1-0.05 μg/mL) are used as inhibition controls, respectively.

Tulbaghia violacea (Harv) Exerts its Antifungal Activity by Reducing Ergosterol Production in Aspergillus flavus

Opportunistic infections in immunosuppressed patients have led to an increase in fungal infections, with Aspergillus being one of the main causative agents. Medicinal plants exhibiting antifungal activity have the potential to be used as chemotherapeutic agents. However, often their mechanisms of action are not fully researched. Tulbaghia violacea exhibits antifungal activity towards Candida, Aspergillus flavus and Aspergillus parasiticus but its mode of action has only recently begun to be investigated. This study aimed to ascertain the effect of T. violacea rhizome extracts on ergosterol production in A. flavus and the mechanism of inhibition. The MIC of a T. violacea rhizome extract against A. flavus was first determined, using a broth dilution assay, to be 15 mg/ml. Thereafter, the culture was subjected to sub-inhibitory concentrations of the extract before sterol intermediates of the ergosterol biosynthetic pathway were isolated and analysed for dose-dependent accumulation. Analysis by reverse-phase HPLC displayed a decline in ergosterol production in a dose-dependent manner when exposed to increasing concentrations of T. violacea extract. Quantification of the sterol intermediates of the ergosterol pathway indicated a definite accumulation of 2,3-oxidosqualene. The results prove that the plant extract affected ergosterol synthesis by inhibiting oxidosqualene cyclase. This prevented the formation of downstream intermediates of the ergosterol pathway ultimately resulting in inhibition of ergosterol production.

1,2,4-Triazole: A Privileged Scaffold for the Development of Potent Antifungal Agents - A Brief Review

Over the past decades, a tremendous rise in invasive fungal infection diseases attributed to the yeast Candida albicans in immunocompromised individuals poses a seriously challenging issue. Another concern is the emergence of multi-drug resistant pathogens to the existing medicines due to their overuse and misuse. It was recently reported that 25-55% of the mortality rate is caused by invasive infection. Despite a large variety of drugs being available to treat invasive candidiasis, only two of them contain a 1,2,4-triazole core, namely Fluconazole and itraconazole, which are efficient in treating infection induced by fungal Candida species. Moreover, long-term therapy associated with azole medications has led to an increase in azole resistance as well as a high risk of toxicity. Despite numerous outstanding achievements in antifungal drug discovery, development of novel, safer and potent antifungal agents while overcoming the resistance problem associated with the current drugs is becoming the main focus of medicinal chemists. Therefore, this review outlines the breakthroughs in medicinal chemistry research regarding 1,2,4- triazole-based derivatives as potential antifungal agents in the past decade. In addition, the structureactivity relationship of these compounds is also discussed.

Investigation of Alternative Therapeutic and Biocidal Options to Combat Antifungal-Resistant Zoonotic Fungal Pathogens Isolated from Companion Animals

Fungal skin infections and iatrogenic disease of companion animals continue to be an ongoing issue for veterinarians, where misdiagnosis or inapt medical treatment result in secondary conditions within animals. The widespread use of antifungals in both modern medicine and agriculture has resulted in concomitant resistance in species, where zoonotic transfer poses a risk to public health. Studies described herein assess the resistance of pathogenic species isolated from companion animals to a battery of conventional antimicrobial agents. Levels of resistance were detected using recognised in vitro methods, where additional novel therapeutic and biocide options were also extensively investigated. Results show high levels of resistance to the three main families of antifungal agents, namely caspofungin, Amp B and fluconazole. Resistance in Candida, Cryptococcal, Aspergillus and Trichophyton species is described herein, highlighting the need for defined species-specific antifungal breakpoints, and for Malassezia and Wickerhamomyces anomalus species which also have zoonotic potential. Novel compound phendione showed promising antimicrobial activity, with MICs determined for both fungal and bacterial species. The biocidal options investigated also showed potential to act as intermediate-level disinfectants, where peracetic acid proved most effective against fungal spore formers.

Oceanapiside, a Marine Natural Product, Targets the Sphingolipid Pathway of Fluconazole-Resistant Candida glabrata

Oceanapiside (OPS), a marine natural product with a novel bifunctional sphingolipid structure, is fungicidal against fluconazole-resistant Candida glabrata at 10 μg/mL (15.4 μM). The fungicidal effect was observed at 3 to 4 h after exposure to cells. Cytological and morphological studies revealed that OPS affects the budding patterns of treated yeast cells with a significant increase in the number of cells with single small buds. In addition, this budding morphology was found to be sensitive in the presence of OPS. Moreover, the number of cells with single medium-sized buds and cells with single large buds were decreased significantly, indicating that fewer cells were transformed to these budding patterns, suggestive of inhibition of polarized growth. OPS was also observed to disrupt the organized actin assembly in C. glabrata, which correlates with inhibition of budding and polarized growth. It was also demonstrated that phytosphingosine (PHS) reversed the antifungal activity of oceanapiside. We quantified the amount of long chain-bases (LCBs) and phytoceramide from the crude extracts of treated cells using LC-ESI-MS. PHS concentration was elevated in extracts of cells treated with OPS when compared with cells treated with miconazole and amphotericin B. Elevated levels of PHS in OPS-treated cells confirms that OPS affects the pathway at a step downstream of PHS synthesis. These results also demonstrated that OPS has a mechanism of action different to those of miconazole and amphotericin B and interdicts fungal sphingolipid metabolism by specifically inhibiting the step converting PHS to phytoceramide.

Genetic and Phenotypic Characterization of in-Host Developed Azole-Resistant Aspergillus flavus Isolates

Aspergillus flavus is a pathogenic fungal species that can cause pulmonary aspergillosis, and triazole compounds are used for the treatment of these infections. Prolonged exposure to azoles may select for compensatory mutations in the A. flavus genome, resulting in azole resistance. Here, we characterize a series of 11 isogenic A. flavus strains isolated from a patient with pulmonary aspergillosis. Over a period of three months, the initially azole-susceptible strain developed itraconazole and voriconazole resistance. Short tandem repeat analysis and whole-genome sequencing revealed the high genetic relatedness of all isolates, indicating an infection with one single isolate. In contrast, the isolates were macroscopically highly diverse, suggesting an adaptation to the environment due to (epi)genetic changes. The whole-genome sequencing of susceptible and azole-resistant strains showed a number of mutations that might be associated with azole resistance. The majority of resistant strains contain a Y119F mutation in the Cyp51A gene, which corresponds to the Y121F mutation found in A. fumigatus. One azole-resistant strain demonstrated a divergent set of mutations, including a V99A mutation in a major facilitator superfamily (MSF) multidrug transporter (AFLA 083950).

Antifungals, arthropods and antifungal resistance prevention: lessons from ecological interactions

Arthropods can produce a wide range of antifungal compounds, including specialist proteins, cuticular products, venoms and haemolymphs. In spite of this, many arthropod taxa, particularly eusocial insects, make use of additional antifungal compounds derived from their mutualistic association with microbes. Because multiple taxa have evolved such mutualisms, it must be assumed that, under certain ecological circumstances, natural selection has favoured them over those relying upon endogenous antifungal compound production. Further, such associations have been shown to persist versus specific pathogenic fungal antagonists for more than 50 million years, suggesting that compounds employed have retained efficacy in spite of the pathogens' capacity to develop resistance. We provide a brief overview of antifungal compounds in the arthropods' armoury, proposing a conceptual model to suggest why their use remains so successful. Fundamental concepts embedded within such a model may suggest strategies by which to reduce the rise of antifungal resistance within the clinical milieu.

Phenomic profiling of a novel sibling species within the Scedosporium complex in Thailand

Background

Scedosporium species are a group of pathogenic fungi, which can be found worldwide around high human-impacted areas. Infections of Scedosporium have been reported in several immunocompromised and immunocompetent patients with a high mortality rate. Recently, we have isolated and identified several Scedosporium strains during an environmental survey in Thailand.

Results

We describe the isolate, TMMI-012, possibly a new species isolated from soils in the Chatuchak public park, Bangkok, Thailand. TMMI-012 is phylogenetically related to the Scedosporium genus and is a sibling to S. boydii but shows distinct morphological and pathological characteristics. It is fast growing and highly resistant to antifungal drugs and abiotic stresses. Pathological studies of in vitro and in vivo models confirm its high virulence and pathogenicity.

Conclusion

TMMI-012 is considered a putative novel Scedosporium species. The high antifungal resistance of TMMI-012 compared with its sibling, Scedosporium species is likely related to its clinical impact on human health.

Insects, Rodents, and Pets as Reservoirs, Vectors, and Sentinels of Antimicrobial Resistance

This paper reviews the occurrence of antimicrobial resistance (AMR) in insects, rodents, and pets. Insects (e.g., houseflies, cockroaches), rodents (rats, mice), and pets (dogs, cats) act as reservoirs of AMR for first-line and last-resort antimicrobial agents. AMR proliferates in insects, rodents, and pets, and their skin and gut systems. Subsequently, insects, rodents, and pets act as vectors that disseminate AMR to humans via direct contact, human food contamination, and horizontal gene transfer. Thus, insects, rodents, and pets might act as sentinels or bioindicators of AMR. Human health risks are discussed, including those unique to low-income countries. Current evidence on human health risks is largely inferential and based on qualitative data, but comprehensive statistics based on quantitative microbial risk assessment (QMRA) are still lacking. Hence, tracing human health risks of AMR to insects, rodents, and pets, remains a challenge. To safeguard human health, mitigation measures are proposed, based on the one-health approach. Future research should include human health risk analysis using QMRA, and the application of in-silico techniques, genomics, network analysis, and ’big data’ analytical tools to understand the role of household insects, rodents, and pets in the persistence, circulation, and health risks of AMR.

A Noncanonical DNA Damage Checkpoint Response in a Major Fungal Pathogen

In order to preserve genome integrity, all cells must mount appropriate responses to DNA damage, including slowing down or arresting the cell cycle to give the cells time to repair the damage and changing gene expression, for example to induce genes involved in DNA repair. The Rad53 protein kinase is a conserved central mediator of these responses in eukaryotic cells, and its extensive phosphorylation upon DNA damage is necessary for its activation and subsequent activity.

DNA damage checkpoints are key guardians of genome integrity. Eukaryotic cells respond to DNA damage by triggering extensive phosphorylation of Rad53/CHK2 effector kinase, whereupon activated Rad53/CHK2 mediates further aspects of checkpoint activation, including cell cycle arrest and transcriptional changes. Budding yeast Candida glabrata, closely related to model eukaryote Saccharomyces cerevisiae, is an opportunistic pathogen characterized by high genetic diversity and rapid emergence of drug-resistant mutants. However, the mechanisms underlying this genetic variability are unclear. We used Western blotting and mass spectrometry to show that, unlike S. cerevisiae, C. glabrata cells exposed to DNA damage did not induce C. glabrata Rad53 (CgRad53) phosphorylation. Furthermore, flow cytometry analysis showed that, unlike S. cerevisiae, C. glabrata cells did not accumulate in S phase upon DNA damage. Consistent with these observations, time-lapse microscopy showed C. glabrata cells continuing to divide in the presence of DNA damage, resulting in mitotic errors and cell death. Finally, transcriptome sequencing (RNAseq) analysis revealed transcriptional rewiring of the DNA damage response in C. glabrata and identified several key protectors of genome stability upregulated by DNA damage in S. cerevisiae but downregulated in C. glabrata, including proliferating cell nuclear antigen (PCNA). Together, our results reveal a noncanonical fungal DNA damage response in C. glabrata, which may contribute to rapidly generating genetic change and drug resistance.

Mechanisms of triazole resistance in Aspergillus fumigatus

The ubiquitous fungal pathogen Aspergillus fumigatus is the primary cause of opportunistic mould infections in humans. Aspergilli disseminate via asexual conidia passively travelling through air currents to germinate within a broad range of environs, wherever suitable nutrients are found. Though the average human inhales hundreds of conidia daily, A. fumigatus invasive infections primarily affect the immunocompromised. At-risk individuals can develop often fatal invasive disease for which therapeutic options are limited. Regrettably, the global insurgence of isolates resistant to the triazoles, the frontline antifungal class used in medicine and agriculture to control A. fumigatus, is complicating the treatment of patients. Triazole antifungal resistance in A. fumigatus has become recognized as a global, yet poorly comprehended, problem. Due to a multitude of factors, the magnitude of resistant infections and their contribution to treatment outcomes are likely underestimated. Current studies suggest that human drug-resistant infections can be either environmentally acquired or de novo host selected during patient therapy. While much concerning development of resistance is yet unknown, recent investigations have revealed assorted underlying mechanisms enabling triazole resistance within individual clinical and environmental isolates. This review will provide an overview of triazole resistance as it is currently understood, as well as highlight some of the prominent biological mechanisms associated with clinical and environmental resistance to triazoles in A. fumigatus.

Comparative Genome Sequence Analyses of Geographic Samples of Aspergillus fumigatus-Relevance for Amphotericin B Resistance

Amphotericin B (AMB) is a major fungicidal polyene agent that has a broad spectrum of action against invasive fungal infections. AMB is typically used as the last-line drug against serious and life-threatening infections when other drugs have failed to eliminate the fungal pathogens. Recently, AMB resistance in Aspergillus fumigatus has become more evident. For example, a high rate of AMB resistance (96%) was noted in the A. fumigatus population in Hamilton, Ontario, Canada. AMB-resistant strains have also been found in other countries. However, the mechanism of AMB resistance remains largely unknown. Here, we investigated the potential genes and mutations associated with AMB resistance using whole-genome sequences and examined AMB resistance distribution among genetic populations. A total of 196 whole-genome sequences representing strains from 11 countries were examined. Analyses of single nucleotide polymorphisms (SNPs) at the whole-genome level revealed that these strains belonged to three divergent genetic clusters, with the majority (90%) of AMB resistant strains located in one of the three clusters, Cluster 2. Our analyses identified over 60 SNPs significantly associated with AMB resistance. Together, these SNPs represent promising candidates from which to investigate the putative molecular mechanisms of AMB resistance and for their potential use in developing rapid diagnostic markers for clinical screening of AMB resistance in A. fumigatus.

Cinnamyl Schiff bases: synthesis, cytotoxic effects and antifungal activity of clinical interest

The aim of this study was to synthesize and investigate the in vitro antifungal properties of 23 cinnamyl Schiff bases. In addition, cytotoxic effects of such cinnamyl Schiff bases against human lung, kidney or red blood cells were also checked. The compounds were synthesized in a single-step, 2 min of reaction under microwave irradiation produced up to 97% yield. Six of the 23 cinnamyl Schiff bases possessed antifungal activities against strains of Candida, Aspergillus, Fonsecaea and, particularly, Cryptococcus species. Indeed, cinnamyl Schiff bases 1 and 23 exhibited minimum inhibitory concentration (MIC) values more than twofold lower than fluconazole (FCZ) against all the Cryptococcus neoformans strains (MIC = 1·33, 1·4 and 5·2 µg ml^-1 , respectively) and Cryptococcus gattii strains (MIC = 5·3, 2·8 and 9·2 µg ml^-1 , respectively) (12 strains of each species) while cinnamyl Schiff base 11 was as potent as FCZ against all strains from both Cryptococcus species. No significant cytotoxic effects were observed for Schiff bases against human lung, kidney or red blood cells, all presenting selective indexes higher than 10. In conclusion, this study revealed cinnamyl Schiff bases, especially 1 and 23, as new lead anticryptococcal agents for the discovery of novel antifungal drugs. SIGNIFICANCE AND IMPACT OF THE STUDY: The occurrence and severity of fungal infections have increased in recent decades due to resistance to available antifungal drugs and the appearance of new emerging pathogens. Thus, the search for new antifungal agents is mandatory. From a series of 23 cinnamyl Schiff bases, two compounds (1 and 23) were interrogated as new anticryptococcal agents without significant cytotoxicity against human lung, kidney or red blood cells. In turns, these new Schiff bases are lead compounds for the discovery of novel antifungal drugs.

Companion and complementary diagnostics for infectious diseases

INTRODUCTION

Companion diagnostics (CDx) are important in oncology therapeutic decision-making, but specific regulatory-approved CDx for infectious disease treatment are officially lacking. While not approved as CDx, several ID diagnostics are used as CDx. The diagnostics community, manufacturers, and regulatory agencies have made major efforts to ensure that diagnostics for new antimicrobials are available at or near release of new agents.

AREAS COVERED

This review highlights the status of Complementary and companion diagnostic (c/CDx) in the infectious disease literature, with a focus on genotypic antimicrobial resistance testing against pathogens as a class of diagnostic tests.

EXPERT OPINION

CRISPR, sepsis markers, and narrow spectrum antimicrobials, in addition to current and emerging technologies, present opportunities for infectious disease c/CDx. Challenges include slow guideline revision, high costs for regulatory approval, lengthy buy in by agencies, discordant pharmaceutical/diagnostic partnerships, and higher treatment costs. The number of patients and available medications used to treat different infectious diseases is well suited to support competing diagnostic tests. However, newer approaches to treatment (for example, narrow spectrum antibiotics), may be well suited for a small number of patients, i.e. a niche market in support of a CDx. The current emphasis is rapid and point-of-care (POC) diagnostic platforms as well as changes in treatment.

Tracking the functional meaning of the human oral-microbiome protein-protein interactions

The interactome - the network of protein-protein interactions (PPIs) within a cell or organism - is technically difficult to assess. Bioinformatic tools can, not only, identify potential PPIs that can be later experimentally validated, but also be used to assign functional meaning to PPIs. Saliva's potential as a non-invasive diagnostic fluid is currently being explored by several research groups. But, in order to fully attain its potential, it is necessary to achieve the full characterization of the mechanisms that take place within this ecosystem. The onset of omics technologies, and specifically of proteomics, delivered a huge set of data that is largely underexplored. Quantitative information relative to proteins within a given context (for example a given disease) can be used by computational algorithms to generate information regarding PPIs. These PPIs can be further analyzed concerning their functional meaning and used to identify potential biomarkers, therapeutic targets, defense and pathogenicity mechanisms. We describe a computational pipeline that can be used to identify and analyze PPIs between human and microbial proteins. The pipeline was tested within the scenario of human PPIs of systemic (Zika Virus infection) and of oral conditions (Periodontal disease) and also in the context of microbial interactions (Candida-Streptococcus) and showed to successfully predict functionally relevant PPIs. The pipeline can be applied to different scientific areas, such as pharmacological research, since a functional meaningful PPI network can provide insights on potential drug targets, and even new uses for existing drugs on the market.

Exploring the resistance mechanisms in Trichosporon asahii: Triazoles as the last defense for invasive trichosporonosis

Trichosporon asahii has recently been recognized as an emergent fungal pathogen able to cause invasive infections in neutropenic cancer patients as well as in critically ill patients submitted to invasive medical procedures and broad-spectrum antibiotic therapy. T. asahii is the main pathogen associated with invasive trichosporonosis worldwide. Treatment of patients with invasive trichosporonosis remains a controversial issue, but triazoles are mentioned by most authors as the best first-line antifungal therapy. There is mounting evidence supporting the claim that fluconazole (FLC) resistance in T. asahii is emerging worldwide. Since 2000, 15 publications involving large collections of T. asahii isolates described non-wild type isolates for FLC and/or voriconazole. However, very few papers have addressed the epidemiology and molecular mechanism of antifungal resistance in Trichosporon spp. Data available suggest that continuous exposure to azoles can induce mutations in the ERG11 gene, resulting in resistance to this class of antifungal drugs. A recent report characterizing T. asahii azole-resistant strains found several genes differentially expressed and highly mutated, including genes related to the Target of Rapamycin (TOR) pathway, indicating that evolutionary modifications on this pathway induced by FLC stress may be involved in developing azole resistance. Finally, we provided new data suggesting that hyperactive efflux pumps may play a role as drug transporters in FLC resistant T. asahii strains.