Itraconazole resistance in Aspergillus fumigatus

Adoptive T-cell therapy for fungal infections in haematology patients

The prolonged immune deficiency resulting from haematopoietic stem cell transplant and chemotherapy predisposes to a high risk of invasive fungal infections. Despite the recent advances in molecular diagnostic testing, early initiation of pre-emptive antifungal therapy and the use of combination pharmacotherapy, mortality from invasive mould infections remain high among recipients of allogeneic stem cell transplant. The increasing incidences of previously rare and drug-resistant strains of fungi present a further clinical challenge. Therefore, there is a need for novel strategies to combat fungal infections in the immunocompromised. Adoptive therapy using in vitro-expanded fungus-specific CD4 cells of the Th-1 type has shown clinical efficacy in murine studies and in a small human clinical study. Several techniques for the isolation and expansion of fungus-specific T cells have been successfully applied. Here we discuss the incidence and changing patterns of invasive fungal diseases, clinical evidence supporting the role of T cells in fungal immunity, methods to expand fungus-specific T cells in the laboratory and considerations surrounding the use of T cells for fungal immunotherapy.

Structure-Functional Characterization of Cytochrome P450 Sterol 14α-Demethylase (CYP51B) from Aspergillus fumigatus and Molecular Basis for the Development of Antifungal Drugs

Aspergillus fumigatus is the opportunistic fungal pathogen that predominantly affects the immunocompromised population and causes 600,000 deaths/year. The cytochrome P450 51 (CYP51) inhibitor voriconazole is currently the drug of choice, yet the treatment efficiency remains low, calling for rational development of more efficient agents. A. fumigatus has two CYP51 genes, CYP51A and CYP51B, which share 59% amino acid sequence identity. CYP51B is expressed constitutively, whereas gene CYP51A is reported to be inducible. We expressed, purified, and characterized A. fumigatus CYP51B, including determination of its substrate preferences, catalytic parameters, inhibition, and x-ray structure in complexes with voriconazole and the experimental inhibitor (R)-N-(1-(2,4-dichlorophenyl)-2-(1H-imidazol-1-yl)ethyl)-4-(5-phenyl-1,3,4-oxadiazol-2-yl)benzamide (VNI). The enzyme demethylated its natural substrate eburicol and the plant CYP51 substrate obtusifoliol at steady-state rates of 17 and 16 min(-1), respectively, but did not metabolize lanosterol, and the topical antifungal drug miconazole was the strongest inhibitor that we identified. The x-ray crystal structures displayed high overall similarity of A. fumigatus CYP51B to CYP51 orthologs from other biological kingdoms but revealed phylum-specific differences relevant to enzyme catalysis and inhibition. The complex with voriconazole provides an explanation for the potency of this relatively small molecule, whereas the complex with VNI outlines a direction for further enhancement of the efficiency of this new inhibitory scaffold to treat humans afflicted with filamentous fungal infections.

Medically important fungi respond to azole drugs: an update

The increased numbers of patients with compromised immune systems in the last three decades have increased the chances of life-threatening fungal infections. Numerous antifungal drugs have been developed in the last 20 years to treat these infections. The largest group, the azoles, inhibits the synthesis of fungal sterols. The use of these fungistatic azoles has subsequently led to the emergence of acquired azole resistance. The most common mechanisms that result in azole resistance include the overexpression or mutation of the azole target enzyme, and overexpression of drug transporters that are responsible for azole efflux from cells. Additional, less-frequent mechanisms have also been identified. Understanding azole resistance mechanisms is crucial for current antifungal treatment and for the future development of new treatment strategies.

Passive surveillance for azole-resistant Aspergillus fumigatus, United States, 2011-2013

A. fumigatus cyp51A–mediated resistance to azole drugs is rare in the United States.

Emergence of Aspergillus fumigatus strains containing mutations that lead to azole resistance has become a serious public health threat in many countries. Nucleotide polymorphisms leading to amino acid substitutions in the lanosterol demethylase gene (cyp51A) are associated with reduced susceptibility to azole drugs. The most widely recognized mutation is a lysine to histidine substitution at aa 98 (L98H) and a duplication of the untranscribed promoter region, together known as TR₃₄/L98H. This mechanism of resistance has been reported in Europe, Asia, and the Middle East, and is associated with resistance to all azole drugs and subsequent treatment failures. To determine whether isolates with this mutation are spreading into the United States, we conducted a passive surveillance–based study of 1,026 clinical isolates of A. fumigatus from 22 US states during 2011–2013. No isolates harboring the TR₃₄/L98H mutation were detected, and MICs of itraconazole were generally low.

Genomic Context of Azole Resistance Mutations in Aspergillus fumigatus Determined Using Whole-Genome Sequencing

A rapid and global emergence of azole resistance has been observed in the pathogenic fungus Aspergillus fumigatus over the past decade. The dominant resistance mechanism appears to be of environmental origin and involves mutations in the cyp51A gene, which encodes a protein targeted by triazole antifungal drugs. Whole-genome sequencing (WGS) was performed for high-resolution single-nucleotide polymorphism (SNP) analysis of 24 A. fumigatus isolates, including azole-resistant and susceptible clinical and environmental strains obtained from India, the Netherlands, and the United Kingdom, in order to assess the utility of WGS for characterizing the alleles causing resistance. WGS analysis confirmed that TR₃₄/L98H (a mutation comprising a tandem repeat [TR] of 34 bases in the promoter of the cyp51A gene and a leucine-to-histidine change at codon 98) is the sole mechanism of azole resistance among the isolates tested in this panel of isolates. We used population genomic analysis and showed that A. fumigatus was panmictic, with as much genetic diversity found within a country as is found between continents. A striking exception to this was shown in India, where isolates are highly related despite being isolated from both clinical and environmental sources across >1,000 km; this broad occurrence suggests a recent selective sweep of a highly fit genotype that is associated with the TR₃₄/L98H allele. We found that these sequenced isolates are all recombining, showing that azole-resistant alleles are segregating into diverse genetic backgrounds. Our analysis delineates the fundamental population genetic parameters that are needed to enable the use of genome-wide association studies to identify the contribution of SNP diversity to the generation and spread of azole resistance in this medically important fungus.

Resistance to azoles in the ubiquitous ascomycete fungus A. fumigatus was first reported from clinical isolates collected in the United States during the late 1980s. Over the last decade, an increasing number of A. fumigatus isolates from the clinic and from nature have been found to show resistance to azoles, suggesting that resistance is emerging through selection by the widespread usage of agricultural azole antifungal compounds. Aspergillosis is an emerging clinical problem, with high rates of treatment failures necessitating the development of new techniques for surveillance and for determining the genome-wide basis of azole resistance in A. fumigatus.

First determination of azole resistance in Aspergillus fumigatus strains carrying the TR34/L98H mutations in Turkey

Aspergillus fumigatus is the most important etiological agent of invasive aspergillosis. Recently, an increasing number of azole-resistant A. fumigatus isolates have been described in various countries. The prevalence of azole resistance was investigated in this study using our culture collection of A. fumigatus isolates collected between 1999 and 2012 from clinical specimens. Seven hundred and forty-six A. fumigatus isolates, collected from 419 patients, were investigated. First, all isolates were screened for resistance to itraconazole by subculturing on Sabouraud dextrose agar that contained 4 mg/L itraconazole. For isolates that grew on the itraconazole containing agar, the in vitro activities of amphotericin B, itraconazole, voriconazole and posaconazole were determined using the Clinical and Laboratory Standards Institute (CLSI) M38-A reference method. After PCR amplification, the full sequence of the cyp51A gene and its promoter region was determined for all in vitro azole-resistant isolates. Itraconazole resistance was found in 10.2% of the A. fumigatus isolates. From 2000 onwards, patients were observed annually with an itraconazole-resistant isolate. According to in vitro susceptibility tests, amphotericin B exhibited good activity against all isolates whereas the azoles were resistant. Sequence analysis of the promoter region and CYP51A gene indicated the presence of TR34/L98H in 86.8% (n = 66) of isolates. This initial analysis of the resistance mechanism of A. fumigatus from Turkey revealed a common TR34/L98H mutation in the cyp51A gene.

Prevalence and mechanism of triazole resistance in Aspergillus fumigatus in a referral chest hospital in Delhi, India and an update of the situation in Asia

Aspergillus fumigatus causes varied clinical syndromes ranging from colonization to deep infections. The mainstay of therapy of Aspergillus diseases is triazoles but several studies globally highlighted variable prevalence of triazole resistance, which hampers the management of aspergillosis. We studied the prevalence of resistance in clinical A. fumigatus isolates during 4 years in a referral Chest Hospital in Delhi, India and reviewed the scenario in Asia and the Middle East. Aspergillus species (n = 2117) were screened with selective plates for azole resistance. The isolates included 45.4% A. flavus, followed by 32.4% A. fumigatus, 15.6% Aspergillus species and 6.6% A. terreus. Azole resistance was found in only 12 (1.7%) A. fumigatus isolates. These triazole resistant A. fumigatus (TRAF) isolates were subjected to (a) calmodulin and β tubulin gene sequencing (b) in vitro antifungal susceptibility testing against triazoles using CLSI M38-A2 (c) sequencing of cyp51A gene and real-time PCR assay for detection of mutations and (d) microsatellite typing of the resistant isolates. TRAF harbored TR₃₄/L98H mutation in 10 (83.3%) isolates with a pan-azole resistant phenotype. Among the remaining two TRAF isolates, one had G54E and the other had three non-synonymous point mutations. The majority of patients were diagnosed as invasive aspergillosis followed by allergic bronchopulmonary aspergillosis and chronic pulmonary aspergillosis. The Indian TR₃₄/L98H isolates had a unique genotype and were distinct from the Chinese, Middle East, and European TR₃₄/L98H strains. This resistance mechanism has been linked to the use of fungicide azoles in agricultural practices in Europe as it has been mainly reported from azole naïve patients. Reports published from Asia demonstrate the same environmental resistance mechanism in A. fumigatus isolates from two highly populated countries in Asia, i.e., China and India and also from the neighboring Middle East.

Azole-resistant aspergillosis

Azole-resistance in Aspergillus fumigatus is emerging and is becoming an increasing problem in the management of aspergillosis. Two types of development of resistance have been described; resistance acquired during azole treatment in an individual patient and through environmental exposure to fungicides. The main molecular mechanism of azole resistance in A. fumigatus is explained by mutations in the cyp51A-gene. The environmental route of resistance development is particularly worrying and may affect all patients whether azole exposed or naïve, and whether suffering from acute or chronic aspergillosis. No management guidelines to assist clinicians confronted with azole-resistant aspergillosis are available and pre-clinical and clinical evidence supporting treatment choices is scarce.

Update on Antifungal Drug Resistance

Invasive fungal infections remain a major source of global morbidity and mortality, especially among patients with underlying immune suppression. Successful patient management requires antifungal therapy. Yet, treatment choices are restricted due to limited classes of antifungal agents and the emergence of antifungal drug resistance. In some settings, the evolution of multidrug-resistant strains insensitive to several classes of antifungal agents is a major concern. The resistance mechanisms responsible for acquired resistance are well characterized and include changes in drug target affinity and abundance, and reduction in the intracellular level of drug by biofilms and efflux pumps. The development of high-level and multidrug resistance occurs through a stepwise evolution of diverse mechanisms. The genetic factors that influence these mechanisms are emerging and they form a complex symphony of cellular interactions that enable the cell to adapt and/or overcome drug-induced stress. Drivers of resistance involve a complex blend of host and microbial factors. Understanding these mechanisms will facilitate development of better diagnostics and therapeutic strategies to overcome and prevent antifungal resistance.

The molecular mechanism of azole resistance in Aspergillus fumigatus: from bedside to bench and back

The growing use of immunosuppressive therapies has resulted in a dramatic increased incidence of invasive fungal infections (IFIs) caused by Aspergillus fumigatus, a common pathogen, and is also associated with a high mortality rate. Azoles are the primary guideline-recommended therapy agents for first-line treatment and prevention of IFIs. However, increased azole usage in medicinal and agricultural settings has caused azole-resistant isolates to repeatedly emerge in the environment, resulting in a significant threat to human health. In this review, we present and summarize current research on the resistance mechanisms of azoles in A. fumigatus as well as efficient susceptibility testing methods. Moreover, we analyze and discuss the putative clinical (bedside) indication of these findings from bench work.

Aspergillus flavus endocarditis of the native mitral valve in a bone marrow transplant patient

Patient: Male, 36

Final Diagnosis: Aspergillus flavus endocarditis

Symptoms: Malaise • fatigue and dyspnea

Medication: —

Clinical Procedure: Mitral vale replacemnet

Specialty: Cardiology

Multiple mechanisms contribute to the development of clinically significant azole resistance in Aspergillus fumigatus

Infections caused by the filamentous fungus Aspergillus fumigatus are a significant clinical issue and represent the second most-common form of fungal infection. Azole drugs are effective against this pathogen but resistant isolates are being found more frequently. Infections associated with azole resistant A. fumigatus have a significantly increased mortality making understanding drug resistance in this organism a priority. The target of azole drugs is the lanosterol α-14 demethylase enzyme encoded by the cyp51A gene in A. fumigatus. Mutations in cyp51A have been described that give rise to azole resistance and been argued to be the primary, if not sole, contributor to azole resistance. Here, I discuss recent developments that indicate multiple mechanisms, including increased expression of ATP-binding cassette (ABC) transporter proteins, contribute to azole resistance. ABC transporters are well-established determinants of drug resistance in other fungal pathogens and seem likely to play a similar role in A. fumigatus.

Mechanisms of Antifungal Drug Resistance

Antifungal therapy is a central component of patient management for acute and chronic mycoses. Yet, treatment choices are restricted because of the sparse number of antifungal drug classes. Clinical management of fungal diseases is further compromised by the emergence of antifungal drug resistance, which eliminates available drug classes as treatment options. Once considered a rare occurrence, antifungal drug resistance is on the rise in many high-risk medical centers. Most concerning is the evolution of multidrug- resistant organisms refractory to several different classes of antifungal agents, especially among common Candida species. The mechanisms responsible are mostly shared by both resistant strains displaying inherently reduced susceptibility and those acquiring resistance during therapy. The molecular mechanisms include altered drug affinity and target abundance, reduced intracellular drug levels caused by efflux pumps, and formation of biofilms. New insights into genetic factors regulating these mechanisms, as well as cellular factors important for stress adaptation, provide a foundation to better understand the emergence of antifungal drug resistance.

Whole-genome comparison of Aspergillus fumigatus strains serially isolated from patients with aspergillosis

The emergence of azole-resistant strains of Aspergillus fumigatus during treatment for aspergillosis occurs by a mutation selection process. Understanding how antifungal resistance mechanisms evolve in the host environment during infection is of great clinical importance and biological interest. Here, we used next-generation sequencing (NGS) to identify mutations that arose during infection by A. fumigatus strains sequentially isolated from two patients, one with invasive pulmonary aspergillosis (IPA) (five isolations) and the other with aspergilloma (three isolations). The serial isolates had identical microsatellite types, but their growth rates and conidia production levels were dissimilar. A whole-genome comparison showed that three of the five isolates from the IPA patient carried a mutation, while 22 mutations, including six nonsynonymous ones, were found among three isolates from the aspergilloma patient. One aspergilloma isolate carried the cyp51A mutation P216L, which is reported to confer azole resistance, and it displayed an MIC indicating resistance to itraconazole. This isolate harbored five other nonsynonymous mutations, some of which were found in the afyap1 and aldA genes. We further identified a large deletion in the aspergilloma isolate in a region containing 11 genes. This finding suggested the possibility that genomic deletions can occur during chronic infection with A. fumigatus. Overall, our results revealed dynamic alterations that occur in the A. fumigatus genome within its host during infection and treatment.

Resistance to antifungals that target CYP51

Fungal diseases are an increasing global burden. Fungi are now recognised to kill more people annually than malaria, whilst in agriculture, fungi threaten crop yields and food security. Azole resistance, mediated by several mechanisms including point mutations in the target enzyme (CYP51), is increasing through selection pressure as a result of widespread use of triazole fungicides in agriculture and triazole antifungal drugs in the clinic. Mutations similar to those seen in clinical isolates as long ago as the 1990s in Candida albicans and later in Aspergillus fumigatus have been identified in agriculturally important fungal species and also wider combinations of point mutations. Recently, evidence that mutations originate in the field and now appear in clinical infections has been suggested. This situation is likely to increase in prevalence as triazole fungicide use continues to rise. Here, we review the progress made in understanding azole resistance found amongst clinically and agriculturally important fungal species focussing on resistance mechanisms associated with CYP51. Biochemical characterisation of wild-type and mutant CYP51 enzymes through ligand binding studies and azole IC50 determinations is an important tool for understanding azole susceptibility and can be used in conjunction with microbiological methods (MIC50 values), molecular biological studies (site-directed mutagenesis) and protein modelling studies to inform future antifungal development with increased specificity for the target enzyme over the host homologue.

Exploring azole antifungal drug resistance in Aspergillus fumigatus with special reference to resistance mechanisms

ABSTRACT: 

Aspergillus fumigatus, a ubiquitously distributed opportunistic pathogen, is the global leading cause of aspergillosis. Azole antifungals play an important role in the management of aspergillosis. However, over a decade, azole resistance in A. fumigatus isolates has been increasingly reported with variable prevalence worldwide and it is challenging the effective management of aspergillosis. The high mortality rates observed in patients with invasive aspergillosis caused by azole-resistant A. fumigatus (ARAF) isolates pose serious challenges to the clinical microbiologist for timely identification of resistance and appropriate therapeutic interventions. The majority of ARAF isolates contain alterations in the cyp51A gene; however, there have been increasing reports on non-cyp51A mutations contributing to azole resistant phenotypes. This review highlights the emergence and various mechanisms implicated in the development of azole resistance in A. fumigatus. We further present recent developments related to the environmental route in the emergence of ARAF isolates and discuss the therapeutic options available.

In vitro studies of the activity of dithiocarbamate organoruthenium complexes against clinically relevant fungal pathogens

The in vitro antifungal activity of nine dirutheniumpentadithiocarbamate complexes C1-C9 was investigated and assessed for its activity against four different fungal species with clinical interest and related to invasive fungal infections (IFIs), such as Candida spp. [C. albicans (two clinical isolates), C. glabrata, C. krusei, C. parapsolisis, C. tropicalis, C.dubliniensis (six clinical isolates)], Paracoccidioides brasiliensis (seven clinical isolates), Cryptococcus neoformans and Sporothrix schenckii. All synthesized complexes C1-C9 and also the free ligands L1-L9 were submitted to in vitro tests against those fungi and the results are very promising, since some of the obtained MIC (minimal inhibitory concentration) values were very low (from 10-6 mol mL-1 to 10-8 mol mL-1) against all investigated clinically relevant fungal pathogens, except for C. glabrata, that the MIC values are close to the ones obtained for fluconazole, the standard antifungal agent tested. Preliminary structure-activity relations (SAR) might be suggested and a strong influence from steric and lipophilic parameters in the antifungal activity can be noticed. Cytotoxicity assays (IC50) showed that the complexes are not as toxic (IC50 values are much higher-30 to 200 fold-than MIC values). These ruthenium complexes are very promising lead compounds for novel antifungal drug development, especially in IFIs, one of most harmful emerging infection diseases (EIDs).

Mutations in the Cyp51A gene and susceptibility to itraconazole in Aspergillus fumigatus isolated from avian farms in France and China

Azole resistance in the fungal pathogen Aspergillus fumigatus is an emerging problem and may develop during azole therapy in humans and animals or exposure to azole fungicides in the environment. To assess the potential risk of azole-resistance emergence in avian farms where azole compounds are used for the control of avian mycoses, we conducted a drug susceptibility study including A. fumigatus isolates from birds and avian farms in France and Southern China. A total number of 175 isolates were analyzed: 57 isolates were collected in France in avian farms where chemoprophylaxis with parconazole was performed; 51 isolates were collected in southern China in avian farms where no chemoprophylaxis was performed; and 67 additional isolates came from the collection of a mycology laboratory. No resistant isolate was detected, and the distribution of minimum inhibitory concentrations was similar for isolates collected in farms with or without azole chemoprophylaxis. For 61 randomly selected isolates, the full coding sequence of the Cyp51A gene was determined to detect mutations. Nine amino acid alterations were found in the target enzyme, 3 of which were new.

Environmental fungicides and triazole resistance in Aspergillus

Fungal diseases are problematic in both human health and agriculture. Treatment options are limited and resistance may emerge. The relatively recent recognition of triazole resistance in Aspergillus fumigatus has prompted questioning of the origin of resistance. While multiple mechanisms are described in clinical isolates from triazole-treated patients, some de novo resistance is also recognised, especially attributable to TR34 /L98H. Such strains probably arose in the environment, and, indeed, multiple studies have now demonstrated TR(34) /L98H triazole resistance strains of A. fumigatus from soil. Docking and other in vitro studies are consistent with environmental resistance induction through exposure to certain triazole fungicides, notably difenoconazole, propiconazole, epoxiconazole, bromuconazole and tebuconazole. This article addresses the potential implications of this issue for both human health and food security.

Breakpoints for antifungal agents: an update from EUCAST focussing on echinocandins against Candida spp. and triazoles against Aspergillus spp

Candida and Aspergillus infections have emerged as significant pathogens in recent decades. During this same time, broad spectrum triazole and echinocandin antifungal agents have been developed and increasingly used. One consequence of widespread use is leading to the emergence of mutants with acquired resistance mutations. Therefore, accurate susceptibility testing and appropriate clinical breakpoints for the interpretation of susceptibility results have become increasingly important. Here we review the underlying methodology by which breakpoints have been selected by EUCAST (European Committee on Antimicrobial Susceptibility Testing). Five parameters are evaluated: dosing regimens used; EUCAST MIC distributions from multiple laboratories, species and compound specific epidemiological cut off values (upper MIC limits of wild type isolates or ECOFFs), pharmacokinetic/pharmacodynamic relationships and targets associated with outcome and finally clinical data by species and MIC when available. The general principles are reviewed followed by a detailed review of the individual aspects for Candida species and the three echinocandins and for Aspergillus and the three mould-active azoles. This review provides an update of the subcommittee on antifungal susceptibility testing (AFST) of the EUCAST methodology and summarises the current EUCAST breakpoints for Candida and Aspergillus. Recommendations about applicability of antifungal susceptibility testing in the routine setting are also included.

Nikkomycin Z is an effective inhibitor of the chytrid fungus linked to global amphibian declines

Fungal infections in humans, wildlife, and plants are a growing concern because of their devastating effects on human and ecosystem health. In recent years, populations of many amphibian species have declined, and some have become extinct due to chytridiomycosis caused by the fungal pathogen Batrachochytrium dendrobatidis. For some endangered amphibian species, captive colonies are the best intermediate solution towards eventual reintroduction, and effective antifungal treatments are needed to cure chytridiomycosis and limit the spread of this pathogen in such survival assurance colonies. Currently, the best accepted treatment for infected amphibians is itraconazole, but its toxic side effects reduce its usefulness for many species. Safer antifungal treatments are needed for disease control. Here, we show that nikkomycin Z, a chitin synthase inhibitor, dramatically alters the cell wall stability of B. dendrobatidis cells and completely inhibits growth of B. dendrobatidis at 250 μM. Low doses of nikkomycin Z enhanced the effectiveness of natural antimicrobial skin peptide mixtures tested in vitro. These studies suggest that nikkomycin Z would be an effective treatment to significantly reduce the fungal burden in frogs infected by B. dendrobatidis.

Oxygen and an extracellular phase transition independently control central regulatory genes and conidiogenesis in Aspergillus fumigatus

Conidiogenesis is the primary process for asexual reproduction in filamentous fungi. As the conidia resulting from the conidiogenesis process are primarily disseminated via air currents and/or water, an outstanding question has been how fungi recognize aerial environments suitable for conidial development. In this study, we documented the somewhat complex development of the conidia-bearing structures, termed conidiophores, from several Aspergillus species in a subsurface (gel-phase) layer of solid media. A subset of the isolates studied was able to develop conidiophores in a gel-phase environment, but exposure to the aeriform environment was required for the terminal developmental transition from phialide cells to conidia. The remaining Aspergilli could not initiate the conidiogenesis process until they were exposed to the aeriform environment. Our observations of conidiophore development in high or low oxygen conditions in both aeriform and gel-phase environments revealed that oxygen and the aeriform state are positive environmental factors for inducing conidiogenesis in most of the aspergilli tested in this study. Transcriptional analysis using A. fumigatus strain AF293 confined to either the aeriform or gel-phase environments revealed that expression of a key regulatory gene for conidiophore development (AfubrlA) is facilitated by oxygen while expression of another regulatory gene controlling conidia formation from phialides (AfuabaA) was repressed regardless of oxygen levels in the gel-embedded environment. Furthermore, by comparing the developmental behavior of conidiation-defective mutants lacking genes controlling various regulatory checkpoints throughout the conidiogenesis pathway, we propose that this aerial response by the fungus requires both oxygen and the phase transition (solid to aeriform), with these environmental signals integrating into the upstream regulatory pathway and central regulatory pathway of conidiogenesis, respectively. Our findings provide not only novel insight into how fungi respond to an aerial environment to trigger development for airborne conidia production but also the relationship between environmental factors and conidiogenesis regulation in aspergilli.

Composite survival index to compare virulence changes in azole-resistant Aspergillus fumigatus clinical isolates

Understanding resistance to antifungal agents in Aspergillus fumigatus is of increasing importance for the treatment of invasive infections in immunocompromised patients. Although a number of molecular resistance mechanisms are described in detail, the potential accompanying virulence changes and impact on clinical outcome have had little attention. We developed a new measure of survival, the composite survival index (CSI) to use as a measure of the virulence properties of A. fumigatus. Using a novel mathematical model we found a strong correlation between the in vitro growth characteristics and virulence in vivo expressed as CSI. Our model elucidates how three critical parameters (the lag phase (τ), decay constant (λ), and growth rate (ν)) interact with each other resulting in a CSI that correlated with virulence. Hence, strains with a long lag phase and high decay constant were less virulent in a murine model of invasive aspergillosis, whereas high virulence for isolates with a high CSI was associated in vitro with rapid growth and short lag phases. Resistant isolates with cyp51A mutations, which account for the majority of azole resistant aspergillosis cases, did not show a lower virulence compared to azole-susceptible isolates. In contrast, the CSI index revealed that a non-cyp51A-mediated resistance mechanism was associated with a dramatic decrease in CSI. Because of its predictive value, the mathematical model developed may serve to explore strain characteristics in vitro to predict virulence in vivo and significantly reduce the number of experimental animals required in such studies. The proposed measure of survival, the CSI can be used more in a general form in survival studies to explore optimal treatment options.

Functional analysis of an ATP-binding cassette transporter protein from Aspergillus fumigatus by heterologous expression in Saccharomyces cerevisiae

Aspergillus fumigatus is the major filamentous fungal pathogen in humans. Although A. fumigatus can be treated with many of the available antifungal drugs, including azole compounds, drug resistant isolates are being recovered at an increasing rate. In other fungal pathogens such as the Candida species, ATP-binding cassette (ABC) transporter proteins play important roles in development of clinically-significant azole resistance phenotypes. Central among these ABC transporter proteins are homologues of the Saccharomyces cerevisiae Pdr5 multidrug transporter. In this work, we test the two A. fumigatus genes encoding proteins sharing the highest degree of sequence similarity to S. cerevisiae Pdr5 for their ability to be function in a heterologous pdr5Δ strain of S. cerevisiae. Expression of full-length cDNAs for these two Afu proteins failed to suppress the drug sensitive phenotype of a pdr5Δ strain and no evidence could be obtained for their expression as green fluorescent protein (GFP) fusions. To improve the expression of one of these Afu ABC transporters (XP_755847), we changed the sequence of the cDNA to use codons corresponding to the major tRNA species in S. cerevisiae. This codon-optimized (CO Afu abcA) cDNA was efficiently expressed in pdr5Δ cells and able to be detected as a GFP fusion protein. The CO Afu abcA did not correct the drug sensitivity of the pdr5Δ strain and exhibited a high degree of perinuclear fluorescence suggesting that this fusion protein was localized to the S. cerevisiae ER. Interestingly, when these experiments were repeated at 37 °C, the CO Afu abcA was able to complement the drug sensitive phenotype of pdr5Δ cells and exhibited less intracellular fluorescence. Additionally, we found that the CO Afu abcA was able to reduce resistance to drugs like phytosphingosine that act via causing mislocalization of amino acid permeases in fungi. These data suggest that the Afu abcA protein can carry out two different functions of Pdr5: drug transport and regulation of protein internalization from the plasma membrane.

Itraconazole: an update on pharmacology and clinical use for treatment of invasive and allergic fungal infections

INTRODUCTION

Fungal infections are a major source of global morbidity and mortality. Itraconazole is a triazole antifungal agent that is widely used for the prevention and treatment of fungal infection. While newer antifungal agents are now available, itraconazole is an orally bioavailable agent with broad-spectrum antifungal activity. Itraconazole remains a useful drug for the management of allergic and invasive mycoses worldwide.

AREAS COVERED

This article provides a summary of the pharmacokinetics, pharmacodynamics and clinical uses of itraconazole. Additionally, the authors summarise the safety and recently described toxicodynamics and discuss the value of therapeutic drug monitoring (TDM) with itraconazole. The following search criteria were constructed in order to identify relevant literature using PubMed and Ovid-MEDLINE: itraconazole, triazole, pharmacokinetics, pharmacodynamics, toxicodynamics and TDM. Relevant abstracts and articles identified from reviewing secondary citations were additionally retrieved and included if relevant.

EXPERT OPINION

Itraconazole remains an important agent in the prevention and treatment of fungal infection. Itraconazole has a broad-spectrum of activity and is available in both an intravenous and oral form making long-term use in chronic mycoses practical. Itraconazole is widely used for the treatment of endemic fungal infections. Pharmacokinetic variability and clinically important drug interactions make TDM of itraconazole an important consideration.

Azole resistant Aspergillus fumigatus: an emerging problem

Azole resistance has appeared recently in Aspergillus fumigatus and increased dangerously in the last decade. The main resistance mechanism is a point mutation of CYP51A, the gene encoding 14α-sterol demethylase, the target enzyme of azole antifungal drugs. This mutation can induce resistance to itraconazole alone or multi-azole resistance. CYP51A mutation can occur in two cases. The first usually concerns patients receiving long-term azole therapy, most of the time for chronic aspergillosis, and involves a wide range of mutations. The second is due to the use of azole fungicides in agriculture. The latter favors a single mutagenesis event: a substitution of leucine for histidine at codon 98 and the tandem repeat of a 34-base pair tandem sequence in the CYP51A gene promoter region. This confers cross-resistance to all azole antifungal drugs. This emerging and environmentally linked issue is of growing concern for the management of antifungal therapy. This mechanism of resistance was first described in the Netherlands and is now reported worldwide. It may have become the leading mechanism of azole resistance in A. fumigatus. Azoles are major agents for the treatment of aspergillosis, and the only oral antifungals. Infection with antifungal-resistant strains is correlated with treatment failure. This emerging phenomenon stresses the urgent need for new preventive strategies (controlled use of antifungals and azole prophylaxis), new diagnostic strategies (early detection of resistance), and new therapeutic strategies in the management of A. fumigatus infections.

Management of chronic pulmonary aspergillosis

Chronic pulmonary aspergillosis (CPA) is a relatively rare, slowly progressive pulmonary syndrome caused by Aspergillus spp. The scarcity of clinical evidence for its management is an important issue. Oral azoles are recommended as the primary treatment of CPA; however, the evidence for their effectiveness is insufficient. Azole-resistant A. fumigatus is rapidly increasing and becoming a serious concern. Because long-term administration of azoles is the mainstay of CPA, azole resistance may pose a serious threat. Furthermore, prolonged oral administration of azoles may lead to increased azole resistance in CPA patients. Therefore, alternative management strategies for CPA must be considered, and one option may involve the use of intravenous antifungals such as echinocandins and polyens. The utility of these antifungals, however, has not been well evaluated and remains controversial because the drugs are expensive and require patients to be admitted to the hospital for their use. New antifungal drugs with novel mechanisms of action are also needed.

Azole resistance in Aspergillus: global status in Europe and Asia

Azole-resistant strains of Aspergillus have been reported from European and Asian countries at varying frequencies. Based on the limited rates of isolation of Aspergillus from clinical samples in routine practice and the limited number of the screening studies carried out so far, the true prevalence of triazole resistance and the rate of multiazole-resistant strains remain partly unknown. Also, available data are mostly for A. fumigatus (complex), thus the situation for non-fumigatus Aspergilli is less clear. In general, exposure of Aspergillus to antifungal agents via medical or environmental (agricultural) use of these compounds appears to have the possible major impact on acquisition of triazole resistance. Azole resistance in Aspergillus remains to be further elucidated by continued surveillance studies. Based on the possible association with agricultural azole use, environmental sampling appears significant as well.

Microbial cytochromes P450: biodiversity and biotechnology. Where do cytochromes P450 come from, what do they do and what can they do for us?

The first eukaryote genome revealed three yeast cytochromes P450 (CYPs), hence the subsequent realization that some microbial fungal genomes encode these proteins in 1 per cent or more of all genes (greater than 100) has been surprising. They are unique biocatalysts undertaking a wide array of stereo- and regio-specific reactions and so hold promise in many applications. Based on ancestral activities that included 14α-demethylation during sterol biosynthesis, it is now seen that CYPs are part of the genes and metabolism of most eukaryotes. In contrast, Archaea and Eubacteria often do not contain CYPs, while those that do are frequently interesting as producers of natural products undertaking their oxidative tailoring. Apart from roles in primary and secondary metabolism, microbial CYPs are actual/potential targets of drugs/agrochemicals and CYP51 in sterol biosynthesis is exhibiting evolution to resistance in the clinic and the field. Other CYP applications include the first industrial biotransformation for corticosteroid production in the 1950s, the diversion into penicillin synthesis in early mutations in fungal strain improvement and bioremediation using bacteria and fungi. The vast untapped resource of orphan CYPs in numerous genomes is being probed and new methods for discovering function and for discovering desired activities are being investigated.

The effect of Aspergillus fumigatus infection on vitamin D receptor expression in cystic fibrosis

RATIONALE

Aspergillus fumigatus (A. fumigatus) in cystic fibrosis (CF) is increasingly recognized. Although allergic bronchopulmonary aspergillosis (ABPA) leads to deterioration of pulmonary function, the effect of A. fumigatus colonization in the absence of ABPA remains unclear.

OBJECTIVES

To address this, we examined individuals with CF with A. fumigatus who were ABPA negative to identify the effects of itraconazole therapy on Aspergillus-induced lung inflammation.

METHODS

The effect of A. fumigatus on nuclear vitamin D receptor (VDR) expression was investigated using qRT-PCR and Western blotting. IL-5 and IL-13 levels were quantified by ELISA. The effect of itraconazole was assessed by a combination of high-resolution computed tomography, lung function test, and microbiological analysis.

MEASUREMENTS AND MAIN RESULTS

We demonstrate that A. fumigatus down-regulates VDR in macrophages and airway epithelial cells and that the fungal metabolite gliotoxin (Gt) is the main causative agent. Gt overcame the positive effect of 1,25-OH vitamin D(3) on VDR expression in vitro, resulting in increased IL-5 and IL-13 production. In vivo, A. fumigatus positivity was associated with increased Gt in CF bronchoalveolar lavage fluid and increased bronchoalveolar lavage fluid levels of IL-5 and IL-13. After airway eradication of A. fumigatus with itraconazole, we observed decreased Gt, IL-5 and IL-13, improved respiratory symptoms, and diminished high-resolution computed tomography mosaic pattern consistent with sustained pulmonary function.

CONCLUSIONS

This study provides a rationale for the therapeutic effect of itraconazole and implied that the therapeutic potential of vitamin D supplementation in preventing ABPA is only feasible with concurrent elimination of A. fumigatus to permit VDR expression and its positive functional consequences.

Susceptibility screening of hyphae-forming fungi with a new, easy, and fast inoculum preparation method

In vitro susceptibility testing of clinically important fungi becomes more and more essential due to the rising number of fungal infections in patients with impaired immune system. Existing standardized microbroth dilution methods for in vitro testing of molds (CLSI, EUCAST) are not intended for routine testing. These methods are very time-consuming and dependent on sporulating of hyphomycetes. In this multicentre study, a new (independent of sporulation) inoculum preparation method (containing a mixture of vegetative cells, hyphae, and conidia) was evaluated. Minimal inhibitory concentrations (MIC) of amphotericin B, posaconazole, and voriconazole of 180 molds were determined with two different culture media (YST and RPMI 1640) according to the DIN (Deutsches Institut für Normung) microdilution assay. 24 and 48 h MIC of quality control strains, tested per each test run, prepared with the new inoculum method were in the range of DIN. YST and RPMI 1640 media showed similar MIC distributions for all molds tested. MIC readings at 48 versus 24 h yield 1 log(2) higher MIC values and more than 90 % of the MICs read at 24 and 48 h were within ± 2 log(2) dilution. MIC end point reading (log(2 MIC-RPMI 1640)-log(2 MIC-YST)) of both media demonstrated a tendency to slightly lower MICs with RPMI 1640 medium. This study reports the results of a new, time-saving, and easy-to-perform method for inoculum preparation for routine susceptibility testing that can be applied for all types of spore-/non-spore and hyphae-forming fungi.

Identification of novel genes conferring altered azole susceptibility in Aspergillus fumigatus

Azoles are currently the mainstay of antifungal treatment both in agricultural and in clinical settings. Although the target site of azole action is well studied, the basis of azole resistance and the ultimate mode of action of the drug in fungi are poorly understood. To gain a deeper insight into these aspects of azole action, restriction-mediated plasmid integration (REMI) was used to create azole sensitive and resistant strains of the clinically important fungus Aspergillus fumigatus. Four azole sensitive insertions and four azole-resistant insertions were characterized. Three phenotypes could be re-created in wild-type AF210 by reintegration of rescued plasmid and a further four could be confirmed by complementation of the mutant phenotype with a copy of the wild-type gene predicted to be disrupted by the original insertional event. Six insertions were in genes not previously associated with azole sensitivity or resistance. Two insertions occur in transporter genes that may affect drug efflux, whereas others may affect transcriptional regulation of sterol biosynthesis genes and NADH metabolism in the mitochondrion. Two insertions are in genes of unknown function.

In vitro combination of anidulafungin and voriconazole against intrinsically azole-susceptible and -resistant Aspergillus spp

In vitro interaction of anidulafungin with voriconazole was tested by a microdilution broth checkerboard technique and an agar diffusion method against 30 Aspergillus clinical isolates belonging to five different species. By using a complete inhibition endpoint, indifferent interactions were observed for 97% of the isolates by the checkerboard technique (FIC index from 0.5 to 2) and for 100% of the isolates by the agar diffusion method (variation of -2 to +1 log(2) dilutions).

Resistance to voriconazole due to a G448S substitution in Aspergillus fumigatus in a patient with cerebral aspergillosis

A voriconazole-resistant isolate of Aspergillus fumigatus was recovered from an immunocompetent patient receiving long-term antifungal therapy for cerebral aspergillosis. A G448S amino acid substitution in the azole target (Cyp51A) was identified as the cause of the resistance phenotype. This article describes the first isolation of a voriconazole-resistant A. fumigatus isolate from an immunocompetent patient in Spain.

Invasive mold infections in chronic granulomatous disease: a 25-year retrospective survey

BACKGROUND

Invasive fungal infection (IFI) represents a life-threatening condition for patients with chronic granulomatous disease (CGD) and causes one-third of deaths in this population. This study offers a descriptive review of invasive mold infection (mIFI) in children with CGD over an extended period of time.

METHODS

In a cohort of patients with CGD registered in the French National database for Primary Immunodeficiency, we performed a retrospective review of proven mIFI episodes (European Organization for Research and Treatment of Cancer/Invasive Fungal Infections Cooperative Group and the National Institute of Allergy and Infectious Diseases Mycoses Study Group 2008 criteria) occurring from 1984 through 2009.

RESULTS

Twenty-nine proven mIFIs were identified in 24 patients. Thirteen (54%) of 24 children were receiving itraconazole prophylaxis. Seven episodes were caused by Aspergillus fumigatus, 10 by Aspergillus nidulans, 2 by Aspergillus species, and 6 by other opportunistic molds (4 patients only had positive pathological examination findings). First proven mIFI occurred later in the group that received itraconazole than in the group without (median time to mIFI, 10 vs 4 years; P < .01), with a higher proportion of infections due to A. nidulans and other opportunistic molds (P < .05). Course of IFI was complex, with the median duration of therapy and hospitalization reaching 446 and 153 days, respectively. Combined antifungal therapy was commonly used. Four patients received geno-identical hematopoietic stem cell transplantation as salvage therapy. Global cure rate among the cohort reached 75%, but sequelae were frequent. Prognosis has improved over time (43% mortality during 1985-1990 vs 6% thereafter; P = .06). Mortality tended to be lower in the group that recieved itraconazole prophylaxis but at the cost of a longer duration of therapy among cured patients.

CONCLUSIONS

Management of mIFI remains challenging in patients with CGD, but significant improvements have been made over the past decade.

The T788G mutation in the cyp51C gene confers voriconazole resistance in Aspergillus flavus causing aspergillosis

With voriconazole (VRC) being approved as the first choice in treating invasive aspergillosis (IA) and its increasing use in treatment, a VRC-resistant strain of Aspergillus flavus, the second leading cause of IA after Aspergillus fumigatus, has emerged. The VRC-resistant strain of A. flavus was isolated for the first time from the surgical lung specimen of an IA patient with no response to VRC therapy. In order to ascertain the mechanism of VRC resistance, the azole target enzyme genes in this strain of A. flavus were cloned and sequenced, and 4 mutations generating amino acid residue substitutions were found in the cyp51C gene. To further determine the role of this mutated gene for VRC resistance in A. flavus, an Agrobacterium tumefaciens-mediated gene replacement approach was applied. Consequently, the mutated cyp51C gene from this A. flavus strain was proven to confer the VRC resistance. Finally, to discern the one out of the four mutations in the cyp51C gene that is responsible for contributing to VRC resistance, a site-directed gene mutagenesis procedure combined with a gene replacement method was performed. As a result, the T788G missense mutation in the cyp51C gene was identified as responsible for VRC resistance in A. flavus. These findings indicated that the detection of this mutation in A. flavus could serve as an indicator for physicians to avoid the use of VRC during IA treatment. Further comprehensive surveillance for antifungal susceptibility, as well as intensive study on the mechanism of azole resistance in A. flavus causing IA, would be required to fully understand this mechanism.

Antifungal resistance and new strategies to control fungal infections

Despite improvement of antifungal therapies over the last 30 years, the phenomenon of antifungal resistance is still of major concern in clinical practice. In the last 10 years the molecular mechanisms underlying this phenomenon were extensively unraveled. In this paper, after a brief overview of currently available antifungals, molecular mechanisms of antifungal resistance will be detailed. It appears that major mechanisms of resistance are essential due to the deregulation of antifungal resistance effector genes. This deregulation is a consequence of point mutations occurring in transcriptional regulators of these effector genes. Resistance can also follow the emergence of point mutations directly in the genes coding antifungal targets. In addition we further describe new strategies currently undertaken to discover alternative therapy targets and antifungals. Identification of new antifungals is essentially achieved by the screening of natural or synthetic chemical compound collections. Discovery of new putative antifungal targets is performed through genome-wide approaches for a better understanding of the human pathogenic fungi biology.

CADRE: the Central Aspergillus Data REpository 2012

The Central Aspergillus Data REpository (CADRE; http://www.cadre-genomes.org.uk) is a public resource for genomic data extracted from species of Aspergillus. It provides an array of online tools for searching and visualising features of this significant fungal genus. CADRE arose from a need within the medical community to understand the human pathogen Aspergillus fumigatus. Due to the paucity of Aspergillus genomic resources 10 years ago, the long-term goal of this project was to collate and maintain Aspergillus genomes as they became available. Since our first release in 2004, the resource has expanded to encompass annotated sequence for eight other Aspergilli and provides much needed support to the international Aspergillus research community. Recent developments, however, in sequencing technology are creating a vast amount of genomic data and, as a result, we shortly expect a tidal wave of Aspergillus data. In preparation for this, we have upgraded the database and software suite. This not only enables better management of more complex data sets, but also improves annotation by providing access to genome comparison data and the integration of high-throughput data.

SREBP-dependent triazole susceptibility in Aspergillus fumigatus is mediated through direct transcriptional regulation of erg11A (cyp51A)

As triazole antifungal drug resistance during invasive Aspergillus fumigatus infection has become more prevalent, the need to understand mechanisms of resistance in A. fumigatus has increased. The presence of two erg11 (cyp51) genes in Aspergillus spp. is hypothesized to account for the inherent resistance of this mold to the triazole fluconazole (FLC). Recently, an A. fumigatus null mutant of a transcriptional regulator in the sterol regulatory element binding protein (SREBP) family, the ΔsrbA strain, was found to have increased susceptibility to FLC and voriconazole (VCZ). In this study, we examined the mechanism engendering the observed increase in A. fumigatus triazole susceptibility in the absence of SrbA. We observed a significant reduction in the erg11A transcript in the ΔsrbA strain in response to FLC and VCZ. Transcript levels of erg11B were also reduced but not to the extent of erg11A. Interestingly, erg11A transcript levels increased upon extended VCZ, but not FLC, exposure. Construction of an erg11A conditional expression strain in the ΔsrbA strain was able to restore erg11A transcript levels and, consequently, wild-type MICs to the triazole FLC. The VCZ MIC was also partially restored upon increased erg11A transcript levels; however, total ergosterol levels remained significantly reduced compared to those of the wild type. Induction of the erg11A conditional strain did not restore the hypoxia growth defect of the ΔsrbA strain. Taken together, our results demonstrate a critical role for SrbA-mediated regulation of ergosterol biosynthesis and triazole drug interactions in A. fumigatus that may have clinical importance.

Rapid induction of multiple resistance mechanisms in Aspergillus fumigatus during azole therapy: a case study and review of the literature

Nine consecutive isogenic Aspergillus fumigatus isolates cultured from a patient with aspergilloma were investigated for azole resistance. The first cultured isolate showed a wild-type phenotype, but four azole-resistant phenotypes were observed in the subsequent eight isolates. Four mutations were found in the cyp51A gene of these isolates, leading to the substitutions A9T, G54E, P216L, and F219I. Only G54 substitutions were previously proved to be associated with azole resistance. Using a Cyp51A homology model and recombination experiments in which the mutations were introduced into a susceptible isolate, we show that the substitutions at codons P216 and F219 were both associated with resistance to itraconazole and posaconazole. A9T was also present in the wild-type isolate and thus considered a Cyp51A polymorphism. Isolates harboring F219I evolved further into a pan-azole-resistant phenotype, indicating an additional acquisition of a non-Cyp51A-mediated resistance mechanism. Review of the literature showed that in patients who develop azole resistance during therapy, multiple resistance mechanisms commonly emerge. Furthermore, the median time between the last cultured wild-type isolate and the first azole-resistant isolate was 4 months (range, 3 weeks to 23 months), indicating a rapid induction of resistance.