Antifungal susceptibility of Aspergillus fumigatus clinical isolates collected from various areas in Japan

Genomic diversity of the pathogenic fungus Aspergillus fumigatus in Japan reveals the complex genomic basis of azole resistance

Aspergillus fumigatus is a pathogenic fungus with a global distribution. The emergence of azole-resistant A. fumigatus (ARAf) other than the TR-mutants is a problem in Japan. Additionally, the genetic diversity of A. fumigatus strains in Japan remains relatively unknown. Here we show the diversity in the A. fumigatus strains isolated in Japan as well as the complexity in the global distribution of the pathogenic strains. First, we analyzed the genome sequences of 171 strains from Japan as well as the antifungal susceptibility of these strains. Next, we conducted a population analysis of 876 strains by combining the available genomic data for strains isolated worldwide, which were grouped in six clusters. Finally, a genome-wide association study identified the genomic loci associated with ARAf strains, but not the TR-mutants. These results highlight the complexity of the genomic mechanism underlying the emergence of ARAf strains other than the TR-mutants.

Optimized Antifungal Therapy for Chronic Pulmonary Aspergillosis

Chronic pulmonary aspergillosis (CPA) represents a spectrum of lung disorders caused by local proliferation of Aspergillus hyphae in individuals with non-systemic or mildly systemic immunodepression or altered pulmonary integrity due to underlying disease. While long-term systemic antifungal treatment is still the mainstay for management, surgery is considered mainly in rarer invasive disease manifestations such as sinusitis and osteomyelitis. Optimal application of existing antifungal agents with suitable pharmacokinetic properties is important for the treatment of diseases such as CPA, which requires long-term use. Appropriate management of side effects by therapeutic drug monitoring, maintenance of adherence, and assessment of drug resistance to Aspergillus can provide safe and effective treatment in the future. Most available antifungal agents for the management of mycoses in humans have disadvantages that can limit their use in clinical practice. By contrast, second generation antifungals such as triazoles have advantages of extended antifungal spectrum and availability in both oral and intravenous formulations. Isavuconazole, a new extended spectrum triazole, has been shown to be effective against Aspergillus. The safety profile and excellent pharmacokinetic characteristics of isavuconazole make it an attractive option for treatment of invasive fungal infections including CPA. With this drug now available in Japan, new evidence is expected to expand treatment options. This review focuses on the selection of antifungal agents based on national and international guidelines and the characteristics of each agent for their appropriate use in CPA.

A novel Zn2-Cys6 transcription factor clcA contributes to copper homeostasis in Aspergillus fumigatus

The filamentous fungus Aspergillus fumigatus is the most important pathogenic fungus among Aspergillus species associated with aspergillosis. A. fumigatus is exposed to diverse environmental stresses in the hosts during infection such as an excess of essential metal copper. To gain further insights into copper homeostasis, we generated an A. fumigatus laboratory evolved strain with increased fitness in copper stress, and identified the mutation in a Zn₂-Cys₆ type transcription factor clcA. We examined the role of clcA using the evolved and ∆clcA strains. The ∆clcA strain exhibited defective growth on minimal medium, PDA and copper-repleted medium, and defective conidiogenesis and conidial pigmentation. We found that clcA was required for the expressions of genes involved in conidiogenesis, conidial pigmentation, and transporters cdr1B and mfsB related to azole resistance. clcA was dispensable for the virulence in silkworm infection model. We report here that clcA plays an important role in hyphal growth, conidiogenesis, and copper adaptation.

Trends in the Prevalence of Amphotericin B-Resistance (AmBR) among Clinical Isolates of Aspergillus Species

The challenges of the invasive infections caused by the resistant Aspergillus species include the limited access to antifungals for treatment and high mortality. This study aimed to provide a global perspective of the prevalence of amphotericin B resistance (AmBR), geographic distribution, and the trend of AmBR from 2010 to 2020. To analyze the prevalence of in vitro AmBR in clinical Aspergillus species, we reviewed the literature and identified a total of 72 articles. AmBR was observed in 1128 out of 3061 Aspergillus terreus (36.8%), 538 out of 3663 Aspergillus flavus (14.9%), 141 out of 2691 Aspergillus niger (5.2%), and 353 out of 17,494 Aspergillus fumigatus isolates (2.01%). An increasing trend in AmB-resistant isolates of A. fumigatus and a decreasing trend in AmB-resistant A. terreus and A. flavus isolates were observed between 2016 and 2020. AmB-resistant A. terreus and A. niger isolates, accounting for 40.4% and 20.9%, respectively, were the common AmB-resistant Aspergillus species in Asian studies. However, common AmB-resistant Aspergillus species reported by European and American studies were A. terreus and A. flavus isolates, accounting for 40.1% and 14.3% in 31 studies from Europe and 25.1% and 11.7% in 14 studies from America, respectively. The prevalence of AmB-resistant A. niger in Asian isolates was higher than in American and European. We found a low prevalence of A. terreus in American isolates (25.1%) compared to Asian (40.4%) and European (40.1%). Future studies should focus on analyzing the trend of AmBR on a regional basis and using the same methodologies.

The accuracy and clinical impact of the morphological identification of Aspergillus species in the age of cryptic species: A single-centre study

BACKGROUND

Aspergillus spp. is identified morphologically without antifungal susceptibility tests (ASTs) in most clinical laboratories. The aim of this study was to examine the clinical impact of the morphological identification of Aspergillus spp. to ensure the adequate clinical management of Aspergillus infections.

PATIENTS/METHODS

Aspergillus isolates (n = 126) from distinct antifungal treatment-naïve patients with aspergillosis were first identified morphologically, followed by species-level identification via DNA sequencing. An AST for itraconazole (ITC) and voriconazole (VRC) was performed on each Aspergillus isolate.

RESULTS

Based on the genetic test results, morphology-based identification was accurate for >95% of the isolates at the species sensu lato level although the test concordance of Aspergillus spp. with low detection rates was low. The rates of cryptic species were found to be 1.2% among the isolates of A. fumigatus complex and 96.8% in the A. niger complex. Cryptic species with lower susceptibilities to antifungal drugs than sensu stricto species among the same Aspergillus section were as follows: The A. lentulus (n = 1) isolates had low susceptibilities to azoles among the A. fumigatus complex species (n = 86), and A. tubingensis isolates (n = 18) exhibited lower susceptibility to azoles among the A. niger complex species (n = 31).

CONCLUSION

Diagnostic accuracy was high at the A. fumigatus and A. niger complex level. However, in the presence of cryptic species, a solely morphological identification was insufficient. Particularly, ITC and VRC might be inappropriate for aspergillosis treatment when the A. niger complex is identified morphologically because it is possible that the Aspergillus isolate is A. tubingensis.

Species identification, antifungal susceptibility, and clinical feature association of Aspergillus section Nigri isolates from the lower respiratory tract

Species of Aspergillus section Nigri are generally identified by molecular genetics approaches, whereas in clinical practice, they are classified as A. niger by their morphological characteristics. This study aimed to investigate whether the species of Aspergillus section Nigri isolated from the respiratory tract vary depending on clinical diagnosis. Forty-four Aspergillus section Nigri isolates isolated from the lower respiratory tracts of 43 patients were collected from February 2012 to January 2017 at the National Hospital Organization (NHO) Tokyo National Hospital. Species identification was carried out based on β-tubulin gene analysis. Drug susceptibility tests were performed according to the Clinical and Laboratory Standards Institute (CLSI) M38 3rd edition, and the clinical characteristics were retrospectively reviewed. A. welwitschiae was isolated most frequently, followed by A. tubingensis. More than half of the A. tubingensis isolates exhibited low susceptibility to azoles in contrast to only one A. welwitschiae isolate. Approximately three quarters of the patients from whom A. welwitschiae was isolated were diagnosed with colonization, whereas more than half the patients from whom A. tubingensis was isolated were diagnosed with chronic pulmonary aspergillosis (CPA). More attention needs to be given to the drug choice for patients with CPA with Aspergillus section Nigri infection because A. tubingensis, which was found to be frequently azole-resistant, was the most prevalent in these patients.

High detection rate of azole-resistant Aspergillus fumigatus after treatment with azole antifungal drugs among patients with chronic pulmonary aspergillosis in a single hospital setting with low azole resistance

The prevalence of azole-resistant Aspergillus fumigatus (ARAF) among chronic pulmonary aspergillosis (CPA) patients treated with azoles in Japan is unknown. The aim of this study was to determine the detection rate of ARAF in isolates from CPA patients who were treated with azoles for varying durations. The potential mechanism of acquiring resistance was examined by sequencing cyp51A and hmg1, two genes associated with ARAF. A. fumigatus isolates (n = 120) were collected from CPA patients (n = 104) between February 2012 and February 2019, at National Hospital Organization Tokyo National Hospital. The isolates were tested for susceptibility to the azole drugs itraconazole (ITCZ) and voriconazole (VRCZ). The detection rate of ARAF among all isolates was 8.3% (n = 10). Of the 10 resistant isolates, eight were ITCZ-resistant and five were VRCZ-resistant. Among 47 isolates obtained from 36 CPA patients who were treated with ITCZ (for an average of 256 days) and/or VRCZ (for an average of 29 days), the resistance rates were 17.0% and 10.6%, respectively. In addition, 46.2% of 13 isolates obtained from CPA patients with ongoing azole treatment at the time of antifungal therapy failure were resistant to azoles. Among the 10 ARAF isolates, a point mutation was detected in cyp51A in seven isolates and in hmg1 in two isolates. ARAF was detected at a high rate in CPA patients, particularly in those with ongoing long-term azole treatment, at the time of azole antifungal therapy failure.

Biosynthesis of β-(1→5)-Galactofuranosyl Chains of Fungal-Type and O-Mannose-Type Galactomannans within the Invasive Pathogen Aspergillus fumigatus

β-(1→5)-Galactofuranosyl residues are widely distributed in the subphylum Pezizomycotina of the phylum Ascomycota. Pezizomycotina includes many plant and animal pathogens. Although the structure of β-(1→5)-galactofuranosyl residues of galactomannans in filamentous fungi was discovered long ago, it remains unclear which enzyme is responsible for biosynthesis of this glycan. Fungal cell wall formation processes are complicated, and information concerning glycosyltransferases is essential for understanding them. In this study, we showed that GfsA and GfsC are responsible for the biosynthesis of all β-(1→5)-galactofuranosyl residues of fungal-type and O-mannose-type galactomannans. The data presented here indicate that β-(1→5)-galactofuranosyl residues are involved in cell growth, conidiation, polarity, and cell surface hydrophobicity. Our new understanding of β-(1→5)-galactofuranosyl residue biosynthesis provides important novel insights into the formation of the complex cell wall structure and the virulence of the members of the subphylum Pezizomycotina.

The pathogenic fungus Aspergillus fumigatus contains galactomannans localized on the surface layer of its cell walls, which are involved in various biological processes. Galactomannans comprise α-(1→2)-/α-(1→6)-mannan and β-(1→5)-/β-(1→6)-galactofuranosyl chains. We previously revealed that GfsA is a β-galactofuranoside β-(1→5)-galactofuranosyltransferase involved in the biosynthesis of β-(1→5)-galactofuranosyl chains. In this study, we clarified the biosynthesis of β-(1→5)-galactofuranosyl chains in A. fumigatus. Two paralogs exist within A. fumigatus: GfsB and GfsC. We show that GfsB and GfsC, in addition to GfsA, are β-galactofuranoside β-(1→5)-galactofuranosyltransferases by biochemical and genetic analyses. GfsA, GfsB, and GfsC can synthesize β-(1→5)-galactofuranosyl oligomers at up to lengths of 7, 3, and 5 galactofuranoses within an established in vitro highly efficient assay of galactofuranosyltransferase activity. Structural analyses of galactomannans extracted from ΔgfsB, ΔgfsC, ΔgfsAC, and ΔgfsABC strains revealed that GfsA and GfsC synthesized all β-(1→5)-galactofuranosyl residues of fungal-type and O-mannose-type galactomannans and that GfsB exhibited limited function in A. fumigatus. The loss of β-(1→5)-galactofuranosyl residues decreased the hyphal growth rate and conidium formation ability and increased the abnormal hyphal branching structure and cell surface hydrophobicity, but this loss is dispensable for sensitivity to antifungal agents and virulence toward immunocompromised mice.

IMPORTANCE β-(1→5)-Galactofuranosyl residues are widely distributed in the subphylum Pezizomycotina of the phylum Ascomycota. Pezizomycotina includes many plant and animal pathogens. Although the structure of β-(1→5)-galactofuranosyl residues of galactomannans in filamentous fungi was discovered long ago, it remains unclear which enzyme is responsible for biosynthesis of this glycan. Fungal cell wall formation processes are complicated, and information concerning glycosyltransferases is essential for understanding them. In this study, we showed that GfsA and GfsC are responsible for the biosynthesis of all β-(1→5)-galactofuranosyl residues of fungal-type and O-mannose-type galactomannans. The data presented here indicate that β-(1→5)-galactofuranosyl residues are involved in cell growth, conidiation, polarity, and cell surface hydrophobicity. Our new understanding of β-(1→5)-galactofuranosyl residue biosynthesis provides important novel insights into the formation of the complex cell wall structure and the virulence of the members of the subphylum Pezizomycotina.

Current Status of Azole-resistant Aspergillus fumigatus Isolates in East Asia

Aspergillus fumigatus is a saprophytic fungus that is a major causative pathogen for aspergillosis. Only a few classes of antifungals are used for treating this life-threatening fungal infection. Azoles are the first-line drugs and are widely used for the management and prophylaxis of aspergillosis. An emerging issue is the increasing incidence of resistant isolates worldwide. In particular, environmentally derived tandem-repeat-type azole-resistant mutations, such as Cyp51A TR34/L98H, and Cyp51A TR46/Y121F/T289A, have emerged over the last decade. In particular, azole-resistant isolates were prevalent in clinical settings in European countries; many of the reports are from the Netherlands, UK, and Germany. In contrast, reports on azole-resistant A. fumigatus isolates from East Asian countries are still few and have only recently begun to increase. Herein, all literature on East Asian azole-resistant A. fumigatus isolates were reviewed, and a complete list of resistant isolates from China, Japan, Taiwan, and Korea is provided. As of this report, the total numbers of tandem-repeat-type azole-resistant isolates are 26, 3, 32, and 1 in China, Japan, Taiwan, and Korea, respectively.

Identification of Two Mannosyltransferases Contributing to Biosynthesis of the Fungal-type Galactomannan α-Core-Mannan Structure in Aspergillus fumigatus

Fungal-type galactomannan (FTGM) is a polysaccharide composed of α-(1 → 2)-/α-(1 → 6)-mannosyl and β-(1 → 5)-/β-(1 → 6)-galactofuranosyl residues located at the outer cell wall of the human pathogenic fungus Aspergillus fumigatus. FTGM contains a linear α-mannan structure called core-mannan composed of 9 or 10 α-(1 → 2)-mannotetraose units jointed by α-(1 → 6)-linkages. However, the enzymes involved in core-mannan biosynthesis remain unknown. We speculated that two putative α-1,2-mannosyltransferase genes in A. fumigatus, Afu5g02740/AFUB_051270 (here termed core-mannan synthase A [CmsA]) and Afu5g12160/AFUB_059750 (CmsB) are involved in FTGM core-mannan biosynthesis. We constructed recombinant proteins for CmsA and detected robust mannosyltransferase activity using the chemically synthesized substrate p-nitrophenyl α-d-mannopyranoside as an acceptor. Analyses of CmsA enzymatic product revealed that CmsA possesses the capacity to transfer a mannopyranoside to the C-2 position of α-mannose. CmsA could also transfer a mannose residue to α-(1 → 2)-mannobiose and α-(1 → 6)-mannobiose and showed a 31-fold higher specific activity toward α-(1 → 6)-mannobiose than toward α-(1 → 2)-mannobiose. Proton nuclear magnetic resonance (¹H-NMR) spectroscopy and gel filtration chromatography of isolated FTGM revealed that core-mannan structures were drastically altered and shortened in disruptant A. fumigatus strains ∆cmsA, ∆cmsB, and ∆cmsA∆cmsB. Disruption of cmsA or cmsB resulted in severely repressed hyphal extension, abnormal branching hyphae, formation of a balloon structure in hyphae, and decreased conidia formation. The normal wild type core-mannan structure and developmental phenotype were restored by the complementation of cmsA and cmsB in the corresponding disruptant strains. These findings indicate that both CmsA, an α-1,2-mannosyltransferase, and CmsB, a putative mannosyltransferase, are involved in FTGM biosynthesis.

Prevalence of azole-resistant Aspergillus fumigatus in the environment of Thailand

Occurrence of azole-resistant Aspergillus fumigatus (ARAF) in the environment is an emerging problem worldwide, likely impacting on patient treatment. Several resistance mutations are thought to have initially arisen through triazole-based fungicide use in agriculture and subsequently being propagated in a similar manner. Here we investigated the prevalence of ARAF in the environment of Thailand and characterized their susceptibility profiles toward clinically used azole compounds along with underlying resistance mutations. Three hundred and eight soil samples were collected and analyzed, out of which 3.25% (n = 10) were positive for ARAF. All isolates obtained were resistant to itraconazole (MIC ≥ 8 μg/ml), two showed additional increased MIC values toward posaconazole (MIC = 0.5 μg/ml), and one other toward voriconazole (MIC = 2 μg/ml). Sequencing of the respective cyp51A genes revealed that eight of the isolates carried the TR34/L98H allele and those two with elevated MIC values to posaconazole the G54R substitution. Although a clear correlation between the use of triazole-based fungicides and isolation of ARAF strains from agricultural lands could not be established for Thailand, but this study clearly demonstrates the spread of globally observed ARAF strains to the environment of South East Asia.

Triazole phenotypes and genotypic characterization of clinical Aspergillus fumigatus isolates in China

This study investigated the triazole phenotype and genotypic of clinical Aspergillus fumigatus isolates from China. We determined the triazole susceptibility profiles of 159 A. fumigatus isolates collected between 2011 and 2015 from four different areas in China tested against 10 antifungal drugs using the Clinical Laboratory Standard Institute M38-A2 method. For the seven itraconazole-resistant A. fumigatus isolates identified in the study, the cyp51A gene, including its promoter region, was sequenced and the mutation patterns were characterized. The resistant isolates were genotyped by microsatellite typing to determine the genetic relatedness to isolates from China and other countries. The frequency of itraconazole resistance in A. fumigatus isolates in our study was 4.4% (7/159). Six of the seven triazole-resistant isolates were recovered from the east and southeast of China, and one from was recovered from the west of China. No resistant isolates were found in the north. Three triazole-resistant isolates exhibited the TR₃₄/L98H mutation, two carried the TR₃₄/L98H/S297T/F495I mutation and one harbored a G54V mutation in the cyp51A gene. Analysis of the microsatellite markers from seven non-wild-type isolates indicated the presence of five unique genotypes, which clustered into two major genetic groups. The cyp51A gene mutations TR₃₄/L98H and TR₃₄/L98H/S297T were the most frequently found mutations, and the G54V mutation was reported for the first time in China. The geographic origin of the triazole-resistant isolates appeared to concentrate in eastern and south-eastern areas, which suggests that routine antifungal susceptibility testing in these areas should be performed for all clinically relevant A. fumigatus isolates to guide antifungal therapy and for epidemiological purposes.

Drug Sensitivity and Resistance Mechanism in Aspergillus Section Nigri Strains from Japan

Aspergillus niger and its related species, known as Aspergillus section Nigri, are ubiquitously distributed across the globe and are often isolated from clinical specimens. In Japan, Aspergillus section Nigri is second most often isolated from clinical specimens following Aspergillus fumigatus We determined the species of Aspergillus section Nigri isolated in Japan by DNA sequencing of partial β-tubulin genes and investigated drug susceptibility by the CLSI M38-A2 method. The collection contained 20 Aspergillus niger, 59 Aspergillus welwitschiae, and 39 Aspergillus tubingensis strains. Drug susceptibility testing revealed 30 to 55% of A. niger, 6.8 to 18.6% of A. welwitschiae, and 79.5 to 89.7% of A. tubingensis isolates to be less susceptible (so-called resistant) to itraconazole (ITC) and/or voriconazole (VRC) according to the epidemiologic cutoff values (ECVs) proposed for A. niger previously. MIC distributions of ITC or VRC showed no remarkable differences between clinical and environmental isolates. When the cyp51A sequences were compared between susceptible and resistant strains, 18 amino acid mutations were specific for resistant isolates of A. niger and A. tubingensis; however, none of them were confirmed to be associated with azole resistance. Three nonrelated A. welwitschiae isolates possessed a partial deletion in cyp51A, likely attributable to being more susceptible to azoles than other isolates. One of five ITC-resistant A. tubingensis isolates showed higher expression of cyp51A than did susceptible strains. Our results show that cyp51A point mutations may have no association with azole resistance but that in some cases the overexpression of cyp51A may lead to the azole resistance in these species.

Triazole Resistance in Aspergillus Species: An Emerging Problem

Aspergillus species are ubiquitous fungal saprophytes found in diverse ecological niches worldwide. Among them, Aspergillus fumigatus is the most prevalent and is largely responsible for the increased incidence of invasive aspergillosis with high mortality rates in some immunocompromised hosts. Azoles are the first-line drugs in treating diseases caused by Aspergillus spp. However, increasing reports in A. fumigatus azole resistance, both in the clinical setting and in the environment, are threatening the effectiveness of clinical and agricultural azole drugs. The azole target is the 14-α sterol demethylase encoded by cyp51A gene and the main mechanisms of resistance involve the integration of tandem repeats in its promoter and/or single point mutations in this gene. In A. fumigatus, azole resistance can emerge in two different scenarios: a medical route in which azole resistance is generated during long periods of azole treatment in the clinical setting and a route of resistance derived from environmental origin due to extended use of demethylation inhibitors in agriculture. The understanding of A. fumigatus azole resistance development and its evolution is needed in order to prevent or minimize its impact. In this article, we review the current situation of azole resistance epidemiology and the predominant molecular mechanisms described based on the resistance acquisition routes. In addition, the clinical implications of A. fumigatus azole resistance and future research are discussed.

A Novel Zn2-Cys6 Transcription Factor AtrR Plays a Key Role in an Azole Resistance Mechanism of Aspergillus fumigatus by Co-regulating cyp51A and cdr1B Expressions

Successful treatment of aspergillosis caused by Aspergillus fumigatus is threatened by an increasing incidence of drug resistance. This situation is further complicated by the finding that strains resistant to azoles, the major antifungal drugs for aspergillosis, have been widely disseminated across the globe. To elucidate mechanisms underlying azole resistance, we identified a novel transcription factor that is required for normal azole resistance in Aspergillus fungi including A. fumigatus, Aspergillus oryzae, and Aspergillus nidulans. This fungal-specific Zn2-Cys6 type transcription factor AtrR was found to regulate expression of the genes related to ergosterol biosynthesis, including cyp51A that encodes a target protein of azoles. The atrR deletion mutant showed impaired growth under hypoxic conditions and attenuation of virulence in murine infection model for aspergillosis. These results were similar to the phenotypes for a mutant strain lacking SrbA that is also a direct regulator for the cyp51A gene. Notably, AtrR was responsible for the expression of cdr1B that encodes an ABC transporter related to azole resistance, whereas SrbA was not involved in the regulation. Chromatin immunoprecipitation assays indicated that AtrR directly bound both the cyp51A and cdr1B promoters. In the clinically isolated itraconazole resistant strain that harbors a mutant Cyp51A (G54E), deletion of the atrR gene resulted in a hypersensitivity to the azole drugs. Together, our results revealed that AtrR plays a pivotal role in a novel azole resistance mechanism by co-regulating the drug target (Cyp51A) and putative drug efflux pump (Cdr1B).

Sensitisation of an Azole-Resistant Aspergillus fumigatus Strain containing the Cyp51A-Related Mutation by Deleting the SrbA Gene

Azoles are widely used for controlling fungal growth in both agricultural and medical settings. The target protein of azoles is CYP51, a lanosterol 14-α-demethylase involved in the biosynthesis of ergosterol. Recently, a novel azole resistance mechanism has arisen in pathogenic fungal species Aspergillus fumigatus. Resistant strains contain a 34-bp or 46-bp tandem repeat (TR) in the promoter of cyp51A, and have disseminated globally in a short period of time. In this study, we investigated whether an azole-resistant strain with a 46-bp TR (TR46/Y121F/T289A) could be sensitised to azoles by deletion of srbA, encoding a direct regulator of cyp51A. The loss of SrbA did not affect colony growth or conidia production, but decreased expression of cyp51A. The srbA deletion strain showed hyper-susceptibility to medical azoles as well as azole fungicides, while its sensitivity to non-azole fungicides was unchanged. This is the first demonstration that deletion of a regulator of cyp51A can sensitise an azole-resistant A. fumigatus strain. This finding may assist in the development of new drugs to help combat life-threatening azole-resistant fungal pathogens.

Triazole Resistance in Aspergillus spp.: A Worldwide Problem?

Since the first description of an azole-resistant A. fumigatus strain in 1997, there has been an increasing number of papers describing the emergence of azole resistance. Firstly reported in the USA and soon after in Europe, it has now been described worldwide, challenging the management of human aspergillosis. The main mechanism of resistance is the modification of the azole target enzyme: 14-α sterol demethylase, encoded by the cyp51A gene; although recently, other resistance mechanisms have also been implicated. In addition, a shift in the epidemiology has been noted with other Aspergillus species (mostly azole resistant) increasingly being reported as causative agents of human disease. This paper reviews the current situation of Aspergillus azole resistance and its implications in the clinical setting.

Diagnostics and susceptibility testing in Aspergillus

Invasive aspergillosis is a major cause of morbidity and mortality in immunosuppressed patients. Early diagnosis and correct antifungal treatment have a direct impact on patient survival. A number of newer diagnostic procedures have been developed as alternatives to conventional microbiological methods. The detection of fungal components, largely antigens and DNA, are used in clinical laboratories to diagnose invasive aspergillosis. Other rapid diagnostic tests have been recently developed with promising results. However, antifungal resistance is becoming an emerging problem. The detection of this resistance is important to administer the proper antifungal agent. This text reviews the novelties on new diagnostics Aspergillus spp.

PROCEDURES

Intrinsic antifungal resistance and mechanisms of secondary resistance to triazoles in A. fumigatus are also reviewed.

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.

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.