Key issues concerning fungistatic versus fungicidal drugs

Optical Nanomotion Detection to Rapidly Discriminate between Fungicidal and Fungistatic Effects of Antifungals on Single-Cell Candida albicans

Candida albicans is an emerging pathogen that poses a significant challenge due to its multidrug-resistant nature. There are two types of antifungal agents, fungicidal and fungistatic, with distinct mechanisms of action against fungal pathogens. Fungicidal agents kill fungal pathogens, whereas fungistatic agents inhibit their growth. The growth can be restored once the agent is removed and favorable conditions are established. Recognizing this difference is crucial as it influences treatment selection and infection prognosis. We present a technique based on optical nanomotion detection (ONMD) (i.e., observing the movement of the cells using an optical microscope) to discriminate rapidly between fungicidal (caspofungin) and fungistatic (fluconazole) drugs. The technique is based on the change in a yeast cell's nanomotion as a function of time during a two-hour treatment with the antifungal of interest followed by a one-hour growth period. The cells are entrapped in microwells in a microfluidic chip, which allows a quick exchange of growth medium and antifungal agent, enabling ONMD measurements on the same individual cells before and after treatment. This procedure permits to discriminate between fungicidal and fungistatic antifungals in less than 3 h, with single-cell resolution by observing if the nanomotion recovers after removing the treatment and reintroducing growth medium (YPD), or continues to drop. The simplicity of the approach holds promise for further development into a user-friendly device for rapid antifungal susceptibility testing (AFST), potentially being implemented in hospitals and medical centers worldwide in developed and developing countries.

Should Empiric Anti-Fungals Be Administered Routinely for All Patients with Perforated Peptic Ulcers? A Critical Review of the Existing Literature

A perforated peptic ulcer (PPU) is a surgical emergency with a high mortality rate. PPUs cause secondary peritonitis due to bacterial and fungal peritoneal contamination. Surgery is the main treatment modality and patient's comorbidites impacts perioperative morbidity and surgical outcomes. Even after surgery, resuscitation efforts should continue. While empiric antibiotics are recommended, the role of empiric anti-fungal treatment is unclear due to a lack of scientific evidence. This literature review demonstrated a paucity of studies evaluating the role of empiric anti-fungals in PPUs, and with conflicting results. Studies were heterogeneous in terms of patient demographics and underlying surgical pathology (PPUs vs. any gastrointestinal perforation), type of anti-fungal agent, timing of administration and duration of use. Other considerations include the need to differentiate between fungal colonization vs. invasive fungal infection. Despite positive fungal isolates from fluid culture, it is important for clinical judgement to identify the right group of patients for anti-fungal administration. Biochemistry investigations including new fungal biomarkers may help to guide management. Multidisciplinary discussions may help in decision making for this conundrum. Moving forward, further research may be conducted to select the right group of patients who may benefit from empiric anti-fungal use.

Azoles activate type I and type II programmed cell death pathways in crop pathogenic fungi

Triazoles are widely used to control pathogenic fungi. They inhibit the ergosterol biosynthetic pathway, but the precise mechanisms leading to fungicidal activities in many fungal pathogens are poorly understood. Here, we elucidate the mode of action of epoxiconazole and metconazole in the wheat pathogen Zymoseptoria tritici and the rice blast fungus Magnaporthe oryzae. We show that both azoles have fungicidal activity and reduce fluidity, but not integrity, of the plasma membrane. This impairs localisation of Cdc15-like F-BAR proteins, resulting in defective actin ring assembly and incomplete septation. However, mutant studies and pharmacological experiments in vitro and in planta show that azole lethality is due to a combination of reactive oxygen species-induced apoptosis and macroautophagy. Simultaneous inhibition of both programmed cell death pathways abolishes azole-induced cell death. Other classes of ergosterol biosynthesis inhibitors also induce apoptosis and macroautophagy, suggesting that activation of these two cell death pathways is a hallmark of ergosterol synthesis-targeting fungicides. This knowledge will inform future crop protection strategies.

Again and Again-Survival of Candida albicans in Urine Containing Antifungals

BACKGROUND

Relapse of Candida albicans urinary tract infection (UTI) is frequent despite appropriate treatment, as commonly used antifungals such fluconazole and flucytosine are only fungistatics. To improve treatment of Candida UTI and decrease relapses, understanding the long-term metabolic activity and survival of C. albicans in urine containing antifungals at minimal inhibitory concentration (MIC) is needed.

METHODS

we monitored the survival, metabolic activity and consumption of glucose and proteins by C. albicans using conventional methods and isothermal microcalorimetry (IMC). We also investigated the influence of dead Candida cells on the growth of their living counterparts.

RESULTS

For 33 days, weak activity was observed in samples containing antifungals in which C. albicans growth rate was reduced by 48%, 60% and 88%, and the lag increased to 172 h, 168 h and 6 h for amphotericin, flucytosine and fluconazole, respectively. The metabolic activity peaks corresponded to the plate counts but were delayed compared to the exhaustion of resources. The presence of dead cells promoted growth in artificial urine, increasing growth rate and reducing lag in similar proportions.

CONCLUSIONS

Even with antifungal treatment, C. albicans relapses are possible. The low metabolic activity of surviving cells leading to regrowth and chlamydospore formation possibly supported by autophagy are likely important factors in relapses.

Antifungal activity of eumelanin-inspired indoylenepheyleneethynylene against Cryptococcus neoformans

Cryptococcus neoformans is an opportunistic fungal pathogen that causes meningitis in >152,000 immunocompromised individuals annually, leading to 112,000 yearly deaths. The four classes of existing antifungal agents target plasma membrane sterols (ergosterol), nucleic acid synthesis, and cell wall synthesis. Existing drugs are not highly effective against Cryptococcus, and antifungal drug resistance is an increasing problem. A novel antimicrobial compound, a eumelanin-inspired indoylenepheyleneethynylene, EIPE-1, was synthesized and has antimicrobial activity against Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MSRA), but not towards Gram-negative organisms. Based on EIPE-1's antibacterial activity, we hypothesized that EIPE-1 could have antifungal activity. For these studies, we tested EIPE-1 against C. neoformans strain H99 and 6 additional cryptococcal clinical isolates. We examined antifungal activity, cytotoxicity, effects on fungal gene expression, and mechanism of action of EIPE-1. Results showed that EIPE-1 has fungicidal effects on seven cryptococcal strains with MICs ranging from 1.56 to 3.125 μg/mL depending on the strain, and it is non-toxic to mammalian cells. We conducted scanning and transmission electron microscopy on the exposed cells to examine structural changes to the organism following EIPE-1 treatment. Cells exposed displayed structural changes to their cell wall and membranes, with internal contents leaking out of the cells. To understand the effect of EIPE-1 on fungal gene expression, RNA sequencing was conducted. Results showed that EIPE-1 affects several processes involved stress response, ergosterol biosynthesis, capsule biosynthesis, and cell wall attachment and remodeling. Therefore, our studies demonstrate that EIPE-1 has antifungal activity against C. neoformans, which affects both cellular structure and gene expression of multiple fungal pathways involved in cell membrane stability and viability.

Screening of Entomopathogenic Fungal Culture Extracts with Honeybee Nosemosis Inhibitory Activity

This study aimed to select the most effective culture extracts for controlling honeybee nosemosis using 342 entomopathogenic fungi of 24 species from 18 genera. The germination inhibitory activity of the fungal culture extract on Nosema ceranae spores was evaluated using an in vitro germination assay method. Among 89 fungal culture extracts showing germination inhibitory activity of approximately 80% or more, 44 fungal culture extracts that maintained their inhibitory activity even at a concentration of 1% were selected. Finally, the honeybee nosemosis inhibitory activity was evaluated using the cultured extracts of five fungal isolates having a Nosema inhibitory activity of approximately 60% or more, even when the extract was removed after treatment. As a result, the proliferation of Nosema spores was reduced by all fungal culture extract treatments. However, only the treatment of the culture extracts from Paecilomyces marquandii 364 and Pochonia bulbillosa 60 showed a reduction in honeybee mortality due to nosemosis. In particular, the extracts of these two fungal isolates also increased the survival of honeybees.

Antifungal activity against Fusarium oxysporum of quinolizidines isolated from three controlled-growth Genisteae plants: structure-activity relationship implications

The Genisteae tribe belongs to the Fabaceae family. The wide occurrence of secondary metabolites, explicitly highlighting the quinolizidine alkaloids (QAs), characterizes this tribe. In the present study, twenty QAs (1-20), including lupanine (1-7), sparteine (8-10), lupanine (11), cytisine and tetrahydrocytisine (12-17), and matrine (18-20)-type QAs were extracted and isolated from leaves of three species (i.e., Lupinus polyphyllus ('rusell' hybrid), Lupinus mutabilis, and Genista monspessulana) belonging to the Genisteae tribe. These plant sources were propagated under greenhouse conditions. The isolated compounds were elucidated by analyzing their spectroscopical data (MS, NMR). The antifungal effect on the mycelial growth of Fusarium oxysporum (Fox) of each isolated QA was then evaluated through the amended medium assay. The best antifungal activity was found to be for compounds 8 (IC₅₀ = 16.5 µM), 9 (IC₅₀ = 7.2 µM), 12 (IC₅₀ = 11.3 µM), and 18 (IC₅₀ = 12.3 µM). The inhibitory data suggest that some QAs could efficiently inhibit Fox mycelium growth depending on particular structural requirements deduced from structure-activity relationship scrutinies. The identified quinolizidine-related moieties can be involved in lead structures to develop further antifungal bioactives against Fox.

Antimicrobial Performance of Innovative Functionalized Surfaces Based on Enamel Coatings: The Effect of Silver-Based Additives on the Antibacterial and Antifungal Activity

Frequently touched surfaces (FTS) that are contaminated with pathogens are one of the main sources of nosocomial infections, which commonly include hospital-acquired and healthcare-associated infections (HAIs). HAIs are considered the most common adverse event that has a significant burden on the public's health worldwide currently. The persistence of pathogens on contaminated surfaces and the transmission of multi-drug resistant (MDR) pathogens by way of healthcare surfaces, which are frequently touched by healthcare workers, visitors, and patients increase the risk of acquiring infectious agents in hospital environments. Moreover, not only in hospitals but also in high-traffic public places, FTS play a major role in the spreading of pathogens. Consequently, attention has been devoted to developing novel and alternative methods to tackle this problem. This study planned to produce and characterize innovative functionalized enameled coated surfaces supplemented with 1% AgNO₃ and 2% AgNO₃. Thus, the antimicrobial properties of the enamels against relevant nosocomial pathogens including the Gram-positive Staphylococcus aureus and the Gram-negative Escherichia coli and the yeast Candida albicans were assessed using the ISO:22196:2011 norm.

Disruption of Iron Homeostasis and Mitochondrial Metabolism Are Promising Targets to Inhibit Candida auris

Fungal infections are a global threat, but treatments are limited due to a paucity in antifungal drug targets and the emergence of drug-resistant fungi such as Candida auris. Metabolic adaptations enable microbial growth in nutrient-scarce host niches, and they further control immune responses to pathogens, thereby offering opportunities for therapeutic targeting. Because it is a relatively new pathogen, little is known about the metabolic requirements for C. auris growth and its adaptations to counter host defenses. Here, we establish that triggering metabolic dysfunction is a promising strategy against C. auris. Treatment with pyrvinium pamoate (PP) induced metabolic reprogramming and mitochondrial dysfunction evident in disrupted mitochondrial morphology and reduced tricarboxylic acid (TCA) cycle enzyme activity. PP also induced changes consistent with disrupted iron homeostasis. Nutrient supplementation experiments support the proposition that PP-induced metabolic dysfunction is driven by disrupted iron homeostasis, which compromises carbon and lipid metabolism and mitochondria. PP inhibited C. auris replication in macrophages, which is a relevant host niche for this yeast pathogen. We propose that PP causes a multipronged metabolic hit to C. auris: it restricts the micronutrient iron to potentiate nutritional immunity imposed by immune cells, and it further causes metabolic dysfunction that compromises the utilization of macronutrients, thereby curbing the metabolic plasticity needed for growth in host environments. Our study offers a new avenue for therapeutic development against drug-resistant C. auris, shows how complex metabolic dysfunction can be caused by a single compound triggering antifungal inhibition, and provides insights into the metabolic needs of C. auris in immune cell environments. IMPORTANCE Over the last decade, Candida auris has emerged as a human pathogen around the world causing life-threatening infections with wide-spread antifungal drug resistance, including pandrug resistance in some cases. In this study, we addressed the mechanism of action of the antiparasitic drug pyrvinium pamoate against C. auris and show how metabolism could be inhibited to curb C. auris proliferation. We show that pyrvinium pamoate triggers sweeping metabolic and mitochondrial changes and disrupts iron homeostasis. PP-induced metabolic dysfunction compromises the utilization of both micro- and macronutrients by C. auris and reduces its growth in vitro and in immune phagocytes. Our findings provide insights into the metabolic requirements for C. auris growth and define the mechanisms of action of pyrvinium pamoate against C. auris, demonstrating how this compound works by inhibiting the metabolic flexibility of the pathogen. As such, our study characterizes credible avenues for new antifungal approaches against C. auris.

Aprepitant, an antiemetic agent, interferes with metal ion homeostasis of Candida auris and displays potent synergistic interactions with azole drugs

With the rapid increase in the frequency of azole-resistant species, combination therapy appears to be a promising tool to augment the antifungal activity of azole drugs against resistant Candida species. Here, we report the effect of aprepitant, an antiemetic agent, on the antifungal activities of azole drugs against the multidrug-resistant Candida auris. Aprepitant reduced the minimum inhibitory concentration (MIC) of itraconazole in vitro, by up to eight-folds. Additionally, the aprepitant/itraconazole combination interfered significantly with the biofilm-forming ability of C. auris by 95 ± 0.13%, and significantly disrupted mature biofilms by 52 ± 0.83%, relative to the untreated control. In a Caenorhabditis elegans infection model, the aprepitant/itraconazole combination significantly prolonged the survival of infected nematodes by ~90% (five days post-infection) and reduced the fungal burden by ~92% relative to the untreated control. Further, this novel drug combination displayed broad-spectrum synergistic interactions against other medically important Candida species such as C. albicans, C. krusei, C. tropicalis, and C. parapsilosis (ƩFICI ranged from 0.08 to 0.31). Comparative transcriptomic profiling and mechanistic studies indicated aprepitant/itraconazole interferes significantly with metal ion homeostasis and compromises the ROS detoxification ability of C. auris. This study presents aprepitant as a novel, potent, and broad-spectrum azole chemosensitizing agent that warrants further investigation.

Effect of chlorogenic and gallic acids combined with azoles on antifungal susceptibility and virulence of multidrug-resistant Candida spp. and Malassezia furfur isolates

Chlorogenic acid (CHA) and gallic acid (GA) are safe natural phenolic compounds that are used as enhancers of some drugs in influencing antioxidant, anticancer, and antibacterial activities. Among fungi, Candida spp. and Malassezia spp. are characterized by an increasing prevalence of multidrug resistance phenomena and by a high morbidity and mortality of their infections. No data are available about the efficacy of CHA and GA combined with azoles on the antifungal susceptibility and on the virulence of both fungi. Therefore, their antifungal and antivirulence effects have been tested in combination with fluconazole (FLZ) or ketoconazole (KTZ) on 23 Candida spp. and 8 M. furfur isolates. Broth microdilution chequerboard, time-kill studies, and extracellular enzymes (phospholipase and hemolytic) activities were evaluated, displaying a synergistic antifungal action between CHA or GA and FLZ or KTZ on C. albicans, C. bovina, and C. parapsilosis, and antagonistic antifungal effects on M. furfur and Pichia kudriavzevii (Candida krusei) isolates. The time-kill studies confirmed the chequerboard findings, showing fungicidal inhibitory effect only when the GA was combined with azoles on Candida strains. However, the combination of phenolics with azoles had no effect on the virulence of the tested isolates. Our study indicates that the combination between natural products and conventional drugs could be an efficient strategy for combating azole resistance and for controlling fungistatic effects of azole drugs.

NO Candida auris: Nitric Oxide in Nanotherapeutics to Combat Emerging Fungal Pathogen Candida auris

Candida auris (C. auris) is an emerging pathogenic fungal species that is especially worrisome due to its high mortality rates and widespread antifungal resistance. Previous studies have demonstrated the efficacy of nitric oxide (NO) nanoparticles on Candida species, and, to our knowledge, this is the first study to investigate the antifungal effects of a NO-generating nanoparticle on C. auris. Six C. auris strains were incubated with a nanoparticle (NAC-SNO-np), which releases N-acetylcysteine S-nitrosothiol (NAC-SNO) and N-acetylcysteine (NAC), and generates NO, through colony forming unit (CFU) assays, and confocal laser scanning microscopy. NAC-SNO-np effectively eradicates planktonic and biofilm C. auris. Across all six strains, 10 mg/mL NAC-SNO-np significantly reduced the number of CFUs (p < 0.05) and demonstrated a >70% decrease in biofilm viability (p < 0.05). NAC-SNO-np effectively eradicates planktonic C. auris and significantly reduces C. auris biofilm formation. Hence, this novel NO-releasing nanoparticle shows promise as a future therapeutic.

Wheldone: Characterization of a Unique Scaffold from the Coculture of Aspergillus fischeri and Xylaria flabelliformis

Wheldone (1) was isolated and elucidated from a coculture of Aspergillus fischeri (NRRL 181) and Xylaria flabelliformis (G536), where secondary metabolite biosynthesis was stimulated by antagonism between these fungi. First observed via in situ analysis between these competing fungal cultures, the conditions were scaled to reproducibly generate 1, whose novel structure was elucidated by one- and two-dimensional NMR and mass spectrometry. Compound 1 displayed cytotoxic activity against breast, ovarian, and melanoma cancer cell lines.

Identification of a Phenylthiazole Small Molecule with Dual Antifungal and Antibiofilm Activity Against Candida albicans and Candida auris

Candida species are a leading source of healthcare infections globally. The limited number of antifungal drugs combined with the isolation of Candida species, namely C. albicans and C. auris, exhibiting resistance to current antifungals necessitates the development of new therapeutics. The present study tested 85 synthetic phenylthiazole small molecules for antifungal activity against drug-resistant C. albicans. Compound 1 emerged as the most potent molecule, inhibiting growth of C. albicans and C. auris strains at concentrations ranging from 0.25–2 µg/mL. Additionally, compound 1 inhibited growth of other clinically-relevant yeast (Cryptococcus) and molds (Aspergillus) at a concentration as low as 0.50 µg/mL. Compound 1 exhibited rapid fungicidal activity, reducing the burden of C. albicans and C. auris below the limit of detection within 30 minutes. Compound 1 exhibited potent antibiofilm activity, similar to amphotericin B, reducing the metabolic activity of adherent C. albicans and C. auris biofilms by more than 66% and 50%, respectively. Furthermore, compound 1 prolonged survival of Caenorhabditis elegans infected with strains of C. albicans and C. auris, relative to the untreated control. The present study highlights phenylthiazole small molecules, such as compound 1, warrant further investigation as novel antifungal agents for drug-resistant Candida infections.

In Vitro Activity of Chlorhexidine Compared with Seven Antifungal Agents against 98 Fusarium Isolates Recovered from Fungal Keratitis Patients

Fungal keratitis is a common but severe eye infection in tropical and subtropical areas of the world. In regions with a temperate climate, the frequency of infection is rising in patients with contact lenses and following trauma. Early and adequate therapy is important to prevent disease progression and loss of vision. The management of Fusarium keratitis is complex, and the optimal treatment is not well defined. We investigated the in vitro activity of chlorhexidine and seven antifungal agents against a well-characterized collection of Fusarium isolates recovered from patients with Fusarium keratitis. The fungus culture collection of the Center of Expertise in Mycology Radboudumc/CWZ was searched for Fusarium isolates that were cultured from cornea scrapings, ocular biopsy specimens, eye swabs, and contact lens fluid containers from patients with suspected keratitis. The Fusarium isolates that were cultured from patients with confirmed keratitis were all identified using conventional and molecular techniques. Antifungal susceptibility testing was performed according to the EUCAST broth microdilution reference method. The antifungal agents tested included amphotericin B, voriconazole, posaconazole, miconazole, natamycin, 5-fluorocytosine, and caspofungin. In addition, the activity of chlorhexidine was determined. The fungal culture collection contained 98 Fusarium isolates of confirmed fungal keratitis cases from 83 Dutch patients and 15 Tanzanian patients. The isolates were collected between 2007 and 2017. Fusarium oxysporum (n = 24, 24.5%) was the most frequently isolated species followed by Fusarium solani sensu stricto (n = 18, 18.4%) and Fusarium petroliphilum (n = 11, 11.2%). Amphotericin B showed the most favorable in vitro inhibition of Fusarium species followed by natamycin, voriconazole, and chlorhexidine, while 5-fluorocytosine, posaconazole, miconazole, and caspofungin showed no relevant inhibiting effect. However, chlorhexidine showed fungicidal activity against 90% of F. oxysporum strains and 100% of the F. solani strains. Our study supports the clinical efficacy of chlorhexidine and therefore warrants its further clinical evaluation for primary therapy of fungal keratitis, particularly in low and middle income countries where fungal keratitis is much more frequent and, currently, antifungal eye drops are often unavailable.

Hybrid Molecules Development: A Versatile Landscape for the Control of Antifungal Drug Resistance: A Review

Hybrid molecule approach of drug design has become popular due to advantages such as delayed resistance, reduced toxicity, ease of treatment of co-infection and lower cost of preclinical evaluation. Antifungal drugs currently available for the treatment of fungal diseases suffer a major side effect of drug resistance. Hybrid drugs development is one of the approaches that has been employed to control microbial resistance. Their antifungal activity is influenced by their design. This review is focused on hybrid molecules exhibiting antifungal properties to guide scientists in search of more efficient drugs for the treatment of fungal diseases.

Antifungal activity of well-defined chito-oligosaccharide preparations against medically relevant yeasts

Due to their antifungal activity, chitosan and its derivatives have potential to be used for treating yeast infections in humans. However, to be considered for use in human medicine, it is necessary to control and know the chemical composition of the compound, which is not always the case for polymeric chitosans. Here, we analyze the antifungal activity of a soluble and well-defined chito-oligosaccharide (CHOS) with an average polymerization degree (DP_n) of 32 and fraction of acetylation (F_A) of 0.15 (C32) on 52 medically relevant yeast strains. Minimal inhibitory concentrations (MIC) varied widely among yeast species, strains and isolates (from > 5000 to < 9.77 μg mL^-1) and inhibition patterns showed a time- and dose-dependencies. The antifungal activity was predominantly fungicidal and was inversely proportional to the pH, being maximal at pH 4.5, the lowest tested pH. Furthermore, antifungal effects of CHOS fractions with varying average molecular weight indicated that those fractions with an intermediate degree of polymerization, i.e. DP 31 and 54, had the strongest inhibitory effects. Confocal imaging showed that C32 adsorbs to the cell surface, with subsequent cell disruption and accumulation of C32 in the cytoplasm. Thus, C32 has potential to be used as a therapy for fungal infections.

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

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

Structure-activity relationship studies of ultra-short peptides with potent activities against fluconazole-resistant Candida albicans

Vulvovaginal candidiasis (VVC) is a genital fungal infection afflicting approximately 75% of women globally and is primarily caused by the yeast Candida albicans. The extensive use of fluconazole, the first-line antifungal drug of choice, has led to the emergence of fluconazole-resistant C. albicans, creating a global clinical concern. This, coupled to the lack of new antifungal drugs entering the market over the past decade, has made it imperative for the introduction of new antifungal drug classes. Peptides with antifungal properties are deemed potential drug candidates due to their rapid membrane-disrupting mechanism of action. By specifically targeting and rapidly disrupting fungal membranes, they reduce the chances of resistance development and treatment duration. In a previous screening campaign involving an antimicrobial peptide library, we identified an octapeptide (IKIKIKIK-NH₂) with potent activity against C. albicans. Herein, we report a structure-activity relationship study on this peptide with the aim of designing a more potent peptide for further development. The lead peptide was then tested against a panel of fluconazole-resistant C. albicans, subjected to a fungicidal/static determination assay, a human dermal fibroblast viability assay and a homozygous profiling assay to gain insights into its mechanism of action and potential for further development as a topical antifungal agent.

Concentration and timing of application reveal strong fungistatic effect of tebuconazole in a Daphnia-microparasitic yeast model

Given the importance of pollutant effects on host-parasite relationships and disease spread, the main goal of this study was to assess the influence of different exposure scenarios for the fungicide tebuconazole (concentration×timing of application) on a Daphnia-microparasitic yeast experimental system. Previous results had demonstrated that tebuconazole is able to suppress Metschnikowia bicuspidata infection at ecologically-relevant concentrations; here, we aimed to obtain an understanding of the mechanism underlying the anti-parasitic (fungicidal or fungistatic) action of tebuconazole. We exposed the Daphnia-yeast system to four nominal tebuconazole concentrations at four timings of application (according to the predicted stage of parasite development), replicated on two Daphnia genotypes, in a fully crossed experiment. An "all-or-nothing" effect was observed, with tebuconazole completely suppressing infection from 13.5μgl^-1 upwards, independent of the timing of tebuconazole application. A follow-up experiment confirmed that the suppression of infection occurred within a narrow range of tebuconazole concentrations (3.65-13.5μgl^-1), although a later application of the fungicide had to be compensated for by a slight increase in concentration to elicit the same anti-parasitic effect. The mechanism behind this anti-parasitic effect seems to be the inhibition of M. bicuspidata sporulation, since tebuconazole was effective in preventing ascospore production even when applied at a later time. However, this fungicide also seemed to affect the vegetative growth of the yeast, as demonstrated by the enhanced negative effect of the parasite (increasing mortality in one of the host genotypes) at a later time of application of tebuconazole, when no signs of infection were observed. Fungicide contamination can thus affect the severity and spread of disease in natural populations, as well as the inherent co-evolutionary dynamics in host-parasite systems.

Investigation of aryl isonitrile compounds with potent, broad-spectrum antifungal activity

Invasive fungal infections present a formidable global public health challenge due to the limited number of approved antifungal agents and the emergence of resistance to the frontline treatment options, such as fluconazole. Three fungal pathogens of significant concern are Candida, Cryptococcus, and Aspergillus given their propensity to cause opportunistic infections in immunocompromised individuals. New antifungal agents composed of unique chemical scaffolds are needed to address this public health challenge. The present study examines the structure-activity relationship of a set of aryl isonitrile compounds that possess broad-spectrum antifungal activity primarily against species of Candida and Cryptococcus. The most potent derivatives are capable of inhibiting growth of these key pathogens at concentrations as low as 0.5µM. Remarkably, the most active compounds exhibit an excellent safety profile and are non-toxic to mammalian cells even at concentrations up to 256µM. The present study lays the foundation for further investigation of aryl isonitrile compounds as a new class of antifungal agents.

Structural Properties and Antifungal Activity against Candida albicans Biofilm of Different Composite Layers Based on Ag/Zn Doped Hydroxyapatite-Polydimethylsiloxanes

Modern medicine is still struggling to find new and more effective methods for fighting off viruses, bacteria and fungi. Among the most dangerous and at times life-threatening fungi is Candida albicans. Our work is focused on surface and structural characterization of hydroxyapatite, silver doped hydroxyapatite and zinc doped hydroxyapatite deposited on a titanium substrate previously coated with polydimethylsiloxane (HAp-PDMS, Ag:HAp-PDMS, Zn:HAp-PDMS) by different techniques: Scanning Electron Microscopy (SEM), Glow Discharge Optical Emission Spectroscopy (GDOES) and Fourier Transform Infrared Spectroscopy (FTIR). The morphological studies revealed that the use of the PDMS polymer as an interlayer improves the quality of the coatings. The structural characterizations of the thin films revealed the basic constituents of both apatitic and PDMS structure. In addition, the GD depth profiles indicated the formation of a composite material as well as the successful embedding of the HAp, Zn:HAp and Ag:HAp into the polymer. On the other hand, in vitro evaluation of the antifungal properties of Ag:HAp-PDMS and Zn:HAp-PDMS demonstrated the fungicidal effects of Ag:HAp-PDMS and the potential antifungal effect of Zn:HAp-PDMS composite layers against C. albicans biofilm. The results acquired in this research complete previous research on the potential use of new complex materials produced by nanotechnology in biomedicine.

Isolation, characterization and mechanism of action of an antimicrobial peptide from Lecythis pisonis seeds with inhibitory activity against Candida albicans

Antimicrobial peptides (AMPs) are produced by a range of organisms as a first line of defense against invaders or competitors. Owing to their broad antimicrobial activity, AMPs have attracted attention as a potential source of chemotherapeutic drugs. The increasing prevalence of infections caused by Candida species as opportunistic pathogens in immunocompromised patients requires new drugs. Lecythis pisonis is a Lecythydaceae tree that grows in Brazil. The AMPs produced by this tree have not been described previously. We describe the isolation of 12 fractions enriched in peptides from L. pisonis seeds. Of the 12 fractions, at 10 μg/ml, the F4 fraction had the strongest growth inhibitory effect (53.7%) in Candida albicans, in addition to a loss of viability of 94.9%. The F4 fraction was separated into seven sub-fractions by reversed-phase chromatography. The F4.7' fraction had the strongest activity at 10 μg/ml, inhibiting C. albicans growth by 38.5% and a 69.3% loss of viability. The peptide in F4.7' was sequenced and was found to be similar to plant defensins. For this reason, the peptide was named L. pisonis defensin 1 (Lp-Def1). The mechanism of action that is responsible for C. albicans inhibition by Lp-Def1 includes a slight increase of reactive oxygen species induction and a significant loss of mitochondrial function. The results described here support the future development of plant defensins, specifically Lp-Def1, as new therapeutic substances against fungi, especially C. albicans.

Antidermatophytic Activity of Mikania micrantha Kunth: An Invasive Weed

CONTEXT

The incidence of dermatophytosis has risen dramatically in recent years. Limited availability of side-effect free drugs has led to a search for new antidermatophytic agents.

OBJECTIVE

The objective was to investigate antidermatophytic activity and in vitro anti-inflammatory activity (protease inhibition assay) of whole plant (aerial parts only) of Mikania micrantha.

MATERIALS AND METHODS

The dried and powdered aerial parts of M. micrantha were extracted separately with petroleum ether, ethyl acetate and methanol. Antidermatophytic activity was determined by agar tube dilution method against Epidermophyton floccosum var. nigricans, Microsporum canis, Microsporum gypseum and Trichophyton rubrum. The activities of various parts of the plant - flowers, leaves and stem were separately analyzed using their ethyl acetate extract. Fungicidal efficacy and trypsin inhibiting activity of the whole plant, flowers and leaves were also analyzed using the ethyl acetate extracts.

STATISTICAL ANALYSIS USED

For trypsin inhibition assay results are expressed as mean ± standard division. For antidermatophytic assay, the significance of the difference between control and test was analyzed statistically using Fisher's exact test.

RESULTS

Ethyl acetate extract of M. micrantha exhibited excellent antidermatophytic activity, followed by petroleum ether and methanolic extracts. Ethyl acetate extracts of whole plant, flowers, leaves and stem completely inhibited the growth of dermatophytes at the tested concentration of 2 mg/mL. Furthermore, ethyl acetate extracts of whole plant, leaves and flowers were fungicidal, and the percentages of trypsin inhibition exhibited were 33.73 ± 0.306, 39.0 ± 0.505 and 35.53 ± 0.503, respectively.

CONCLUSIONS

Since M. micrantha possesses antidermatophytic as well as anti-inflammatory activities, the plant is an excellent candidate for the development of new medicaments against dermatophytoses in traditional as well as modern medicine.

Ultrastructural analysis of Candida albicans when exposed to silver nanoparticles

Candida albicans is the most common fungal pathogen in humans, and recently some studies have reported the antifungal activity of silver nanoparticles (AgNPs) against some Candida species. However, ultrastructural analyses on the interaction of AgNPs with these microorganisms have not been reported. In this work we evaluated the effect of AgNPs on C. albicans, and the minimum inhibitory concentration (MIC) was found to have a fungicidal effect. The IC₅₀ was also determined, and the use of AgNPs with fluconazole (FLC), a fungistatic drug, reduced cell proliferation. In order to understand how AgNPs interact with living cells, the ultrastructural distribution of AgNPs in this fungus was determined. Transmission electron microscopy (TEM) analysis revealed a high accumulation of AgNPs outside the cells but also smaller nanoparticles (NPs) localized throughout the cytoplasm. Energy dispersive spectroscopy (EDS) analysis confirmed the presence of intracellular silver. From our results it is assumed that AgNPs used in this study do not penetrate the cell, but instead release silver ions that infiltrate into the cell leading to the formation of NPs through reduction by organic compounds present in the cell wall and cytoplasm.

Genetic diversity and antifungal susceptibility profiles in causative agents of sporotrichosis

Background

Sporotrichosis is a chronic subcutaneous mycosis of humans and animals, which is typically acquired by traumatic inoculation of plant material contaminated with Sporothrix propagules, or via animals, mainly felines. Sporothrix infections notably occur in outbreaks, with large epidemics currently taking place in southeastern Brazil and northeastern China. Pathogenic species include Sporothrix brasiliensis, Sporothrix schenckii s. str., Sporothrix globosa, and Sporothrix luriei, which exhibit differing geographical distribution, virulence, and resistance to antifungals. The phylogenetically remote species Sporothrix mexicana also shows a mild pathogenic potential.

Methods

We assessed a genetically diverse panel of 68 strains. Susceptibility profiles of medically important Sporothrix species were evaluated by measuring the MICs and MFCs for amphotericin B (AMB), fluconazole (FLC), itraconazole (ITC), voriconazole (VRC), posaconazole (PCZ), flucytosine (5FC), and caspofungin (CAS). Haplotype networks were constructed to reveal interspecific divergences within clinical Sporothrix species to evaluate genetically deviant isolates.

Results

ITC and PCZ were moderately effective against S. brasiliensis (MIC₉₀ = 2 and 2 μg/mL, respectively) and S. schenckii (MIC₉₀ = 4 and 2 μg/mL, respectively). PCZ also showed low MICs against the rare species S. mexicana. 5FC, CAS, and FLC showed no antifungal activity against any Sporothrix species. The minimum fungicidal concentration ranged from 2 to >16 μg/mL for AMB against S. brasiliensis and S. schenckii, while the MFC₉₀ was >16 μg/mL for ITC, VRC, and PCZ.

Conclusion

Sporothrix species in general showed high degrees of resistance against antifungals. Evaluating a genetically diverse panel of strains revealed evidence of multidrug resistant phenotypes, underlining the need for molecular identification of etiologic agents to predict therapeutic outcome.

Synergism of antifungal activity between mitochondrial respiration inhibitors and kojic acid

Co-application of certain types of compounds to conventional antimicrobial drugs can enhance the efficacy of the drugs through a process termed chemosensitization. We show that kojic acid (KA), a natural pyrone, is a potent chemosensitizing agent of complex III inhibitors disrupting the mitochondrial respiratory chain in fungi. Addition of KA greatly lowered the minimum inhibitory concentrations of complex III inhibitors tested against certain filamentous fungi. Efficacy of KA synergism in decreasing order was pyraclostrobin > kresoxim-methyl > antimycin A. KA was also found to be a chemosensitizer of cells to hydrogen peroxide (H₂O₂), tested as a mimic of reactive oxygen species involved in host defense during infection, against several human fungal pathogens and Penicillium strains infecting crops. In comparison, KA-mediated chemosensitization to complex III inhibitors/H₂O₂ was undetectable in other types of fungi, including Aspergillus flavus, A. parasiticus, and P. griseofulvum, among others. Of note, KA was found to function as an antioxidant, but not as an antifungal chemosensitizer in yeasts. In summary, KA could serve as an antifungal chemosensitizer to complex III inhibitors or H₂O₂ against selected human pathogens or Penicillium species. KA-mediated chemosensitization to H₂O₂ seemed specific for filamentous fungi. Thus, results indicate strain- and/or drug-specificity exist during KA chemosensitization.

Enhancement of commercial antifungal agents by Kojic Acid

Natural compounds that pose no significant medical or environmental side effects are potential sources of antifungal agents, either in their nascent form or as structural backbones for more effective derivatives. Kojic acid (KA) is one such compound. It is a natural by-product of fungal fermentation commonly employed by food and cosmetic industries. We show that KA greatly lowers minimum inhibitory (MIC) or fungicidal (MFC) concentrations of commercial medicinal and agricultural antifungal agents, amphotericin B (AMB) and strobilurin, respectively, against pathogenic yeasts and filamentous fungi. Assays using two mitogen-activated protein kinase (MAPK) mutants, i.e., sakAΔ, mpkCΔ, of Aspergillus fumigatus, an agent for human invasive aspergillosis, with hydrogen peroxide (H₂O₂) or AMB indicate such chemosensitizing activity of KA is most conceivably through disruption of fungal antioxidation systems. KA could be developed as a chemosensitizer to enhance efficacy of certain conventional antifungal drugs or fungicides.

Enhancement of antimycotic activity of amphotericin B by targeting the oxidative stress response of Candida and cryptococcus with natural dihydroxybenzaldehydes

In addition to the fungal cellular membrane, the cellular antioxidant system can also be a viable target in the antifungal action of amphotericin B (AMB). Co-application of certain redox-potent natural compounds with AMB actually increases efficacy of the drug through chemosensitization. Some redox-potent chemosensitizers and AMB perturb common cellular targets, resulting in synergistic inhibition of fungal growth. Chemosensitizing activities of four redox-potent benzaldehydes were tested against clinical and reference strains of Candida albicans, C. krusei, C. tropicalis, and Cryptococcus neoformans in combination with AMB, based on assays outlined by the European Committee on Antimicrobial Susceptibility Testing. Two dihydroxybenzaldehydes (DHBAs), i.e., 2,3-DHBA and 2,5-DHBA, significantly enhanced activity of AMB against most strains, as measured by lower minimum inhibitory concentrations and/or minimum fungicidal concentrations (MFCs). A non-hydroxylated benzaldehyde, trans-cinnamaldehyde, showed chemosensitizing activity through lower MFCs, only. Contrastingly, a methoxylated benzaldehyde (3,5-dimethoxybenzaldehyde) had no chemosensitizing activity, as all strains were hypertolerant to this compound. Bioassays using deletion mutants of the model yeast, Saccharomyces cerevisiae, indicated DHBAs exerted their chemosensitizing activity by targeting mitochondrial superoxide dismutase. This targeting, in turn, disrupted the ability of the yeast strains to respond to AMB-induced oxidative stress. These in vitro results indicate that certain DHBAs are potent chemosensitizing agents to AMB through co-disruption of the oxidative stress response capacity of yeasts. Such redox-potent compounds show promise for enhancing AMB-based antifungal therapy for candidiasis and cryptococcosis.

Targeting the oxidative stress response system of fungi with redox-potent chemosensitizing agents

The cellular antioxidant system is a target in the antifungal action of amphotericin B (AMB) and itraconazole (ITZ), in filamentous fungi. The sakAΔ mutant of Aspergillus fumigatus, a mitogen-activated protein kinase (MAPK) gene deletion mutant in the antioxidant system, was found to be more sensitive to AMB or ITZ than other A. fumigatus strains, a wild type and a mpkCΔ mutant (a MAPK gene deletion mutant in the polyalcohol sugar utilization system). Complete fungal kill (≥99.9%) by ITZ or AMB was also achieved by much lower dosages for the sakAΔ mutant than for the other strains. It appears msnA, an Aspergillus ortholog to Saccharomyces cerevisiaeMSN2 (encoding a stress-responsive C₂H₂-type zinc-finger regulator) and sakA and/or mpkC (upstream MAPKs) are in the same stress response network under tert-butyl hydroperoxide (t-BuOOH)-, hydrogen peroxide (H₂O₂)- or AMB-triggered toxicity. Of note is that ITZ-sensitive yeast pathogens were also sensitive to t-BuOOH, showing a connection between ITZ sensitivity and antioxidant capacity of fungi. Enhanced antifungal activity of AMB or ITZ was achieved when these drugs were co-applied with redox-potent natural compounds, 2,3-dihydroxybenzaldehyde, thymol or salicylaldehyde, as chemosensitizing agents. We concluded that redox-potent compounds, which target the antioxidant system in fungi, possess a chemosensitizing capacity to enhance efficacy of conventional drugs.

Antifungal activity of redox-active benzaldehydes that target cellular antioxidation

Background

Disruption of cellular antioxidation systems should be an effective method for control of fungal pathogens. Such disruption can be achieved with redox-active compounds. Natural phenolic compounds can serve as potent redox cyclers that inhibit microbial growth through destabilization of cellular redox homeostasis and/or antioxidation systems. The aim of this study was to identify benzaldehydes that disrupt the fungal antioxidation system. These compounds could then function as chemosensitizing agents in concert with conventional drugs or fungicides to improve antifungal efficacy.

Methods

Benzaldehydes were tested as natural antifungal agents against strains of Aspergillus fumigatus, A. flavus, A. terreus and Penicillium expansum, fungi that are causative agents of human invasive aspergillosis and/or are mycotoxigenic. The yeast Saccharomyces cerevisiae was also used as a model system for identifying gene targets of benzaldehydes. The efficacy of screened compounds as effective chemosensitizers or as antifungal agents in formulations was tested with methods outlined by the Clinical Laboratory Standards Institute (CLSI).

Results

Several benzaldehydes are identified having potent antifungal activity. Structure-activity analysis reveals that antifungal activity increases by the presence of an ortho-hydroxyl group in the aromatic ring. Use of deletion mutants in the oxidative stress-response pathway of S. cerevisiae (sod1Δ, sod2Δ, glr1Δ) and two mitogen-activated protein kinase (MAPK) mutants of A. fumigatus (sakAΔ, mpkCΔ), indicates antifungal activity of the benzaldehydes is through disruption of cellular antioxidation. Certain benzaldehydes, in combination with phenylpyrroles, overcome tolerance of A. fumigatus MAPK mutants to this agent and/or increase sensitivity of fungal pathogens to mitochondrial respiration inhibitory agents. Synergistic chemosensitization greatly lowers minimum inhibitory (MIC) or fungicidal (MFC) concentrations. Effective inhibition of fungal growth can also be achieved using combinations of these benzaldehydes.

Conclusions

Natural benzaldehydes targeting cellular antioxidation components of fungi, such as superoxide dismutases, glutathione reductase, etc., effectively inhibit fungal growth. They possess antifungal or chemosensitizing capacity to enhance efficacy of conventional antifungal agents. Chemosensitization can reduce costs, abate resistance, and alleviate negative side effects associated with current antifungal treatments.

A high-throughput assay of yeast cell lysis for drug discovery and genetic analysis

The identification of new antifungal molecules is an important goal of current anti-infective research. To achieve this goal, alternatives to traditional growth inhibition-based screening have been developed in recent years. In this study, we describe an assay to detect molecules that disrupt yeast cell integrity by using the release of adenylate kinase (AK) into culture medium as a reporter of yeast cell lysis. The protocol is applicable to 96- and 384-well microtiter plate formats; uses a commercially available luminescence assay kit to detect AK activity; is more sensitive than traditional growth-based assays; and is specific for fungicidal compounds. In the high-throughput setting, the procedure provides excellent Z' scores (0.75-0.9), making it a highly robust assay. The AK assay is performed in a single microtiter plate using an 'add and read' procedure that can be completed in a single work day.

Breakthrough Scedosporium apiospermum (Pseudallescheria boydii) brain abscess during therapy for invasive pulmonary aspergillosis following high-risk allogeneic hematopoietic stem cell transplantation. Scedosporiasis and recent advances in antifungal therapy

Systemic scedosporiasis due to the anamorph or asexual form Scedosporium apiospermum (Pseudallescheria boydii) has become an important cause of opportunistic mycosis, especially in patients undergoing high-risk hematopoietic stem cell transplantation. We report a case of rapidly progressive cerebellar hyalohyphomycosis due to Scedosporium apiospermum in an allogeneic marrow graft recipient receiving treatment for severe graft-versus-host disease. This fatal breakthrough intracranial abscess, due to amphotericin B-resistant (minimum inhibitory concentration > 16 micro g/ml) mold, developed during the course of systemic antifungal therapy given for multicentric pulmonary aspergillosis. Despite treatment with high-dose Abelcet (10 mg/kg daily), free amphotericin B was not detected in postmortem cerebellar tissue. A broad-spectrum triazole-based agent (voriconazole/UK-109, 496--Vfend), and a novel fungal cell wall inhibitor, an echinocandin/pneumocandin analog (caspofungin/MK-0991--Cancidas), which exhibit excellent in vitro activity against most clinical Pseudallescheria boydii-Scedosporium apiospermum isolates, have recently become available in the United States and may provide much needed treatment options for patients at risk.

Infectious morbidity in critically ill patients with cancer

Infection frequently complicates the course of cancer treatment and often adversely affects the outcome. Patients have a greater tendency for acquiring infections caused by opportunistic microorganisms. Agents with low virulence potential may lead to invasive and often life-threatening infections because of altered host immune function. The immune dysfunction may be caused by the underlying malignancy, by antineoplastic chemotherapy, or by invasive procedures during supportive care.

Current and future approaches to antimycotic treatment in the era of resistant fungi and immunocompromised hosts

Due to the ever-increasing number of immunocompromised patients, both localised and life-threatening systemic fungal infections are on the increase. Conventional treatment is of limited help, not in the least due to a less optimum benefit-to-risk ratio. Moreover, emerging pathogens with reduced antimicrobial susceptibility and the development of resistance in Candida albicans form a new challenge. Fortunately, conventional antimycotics have been improved and entirely new ones are on the horizon as well as alternative approaches such as immunoreconstitution.

[Review article. Molecular basis of antimycotic therapy]

A review is presented on the hitherto clinically administered antimycotic drugs, their action mechanisms and limitations as well as on the presently newly developed antifungals and their molecular targets.