Azole-Resistant Aspergillosis: Epidemiology, Molecular Mechanisms, and Treatment

Aspergillus fumigatus Cyp51A and Cyp51B Proteins Are Compensatory in Function and Localize Differentially in Response to Antifungals and Cell Wall Inhibitors

Triazole antifungals are the primary therapeutic option against invasive aspergillosis. However, resistance to azoles has increased dramatically over the last decade. Azole resistance is known to primarily occur due to point mutations in the azole target protein Cyp51A, one of two paralogous 14-α sterol demethylases found in Aspergillus fumigatus Despite the importance of Cyp51A, little is known about the function of its paralog, Cyp51B, and the behavior of these proteins within the cell or their functional interrelationship. In this study, we addressed two important aspects of the Cyp51 proteins: (i) we characterized their localization patterns under normal growth versus stress conditions, and (ii) we determined how the proteins compensate for each other's absence and respond to azole treatment. Both the Cyp51A and Cyp51B proteins were found to localize in distinct endoplasmic reticulum (ER) domains, including the perinuclear ER and the peripheral ER. Occasionally, the Cyp51 proteins concentrated in the peripheral ER network of tubules along the hyphal septa and at the hyphal tips. Exposure to voriconazole, caspofungin, and Congo red led to significant increases in fluorescence intensity in these alternative localization sites, indicative of Cyp51 protein translocation in response to cell wall stress. Furthermore, deletion of either Cyp51 paralog increased susceptibility to voriconazole, though a greater effect was observed following deletion of cyp51A, indicating a compensatory response to stress conditions.

Five-Year Survey (2014 to 2018) of Azole Resistance in Environmental Aspergillus fumigatus Isolates from China

A total of 191 soil samples from Hangzhou, China, were submitted to detect non-wild-type (non-WT) Aspergillus fumigatus and its associated mechanisms. There were 2 (4.7%), 13 (12.4%), and 31 (23.1%) isolates identified as non-WT in 2014, 2016, and 2018, respectively. The resistant mutations of TR34/L98H, TR46/Y121F/T289A, and TR34/L98H/S297T/F495I were found in 3, 5, and 5 non-WT isolates. The G448S mutation, previously only found in clinical settings, was detected in A. fumigatus from soil samples.

Colistin and Isavuconazole Interact Synergistically In Vitro against Aspergillus nidulans and Aspergillus niger

The in vitro interactions of isavuconazole in combination with colistin were evaluated against 55 clinical Aspergillus species isolates belonging to the five most important species (Aspergillus flavus, Aspergillus fumigatus, Aspergillus nidulans, Aspergillus niger, and Aspergillus terreus) responsible for human aspergillosis by a microdilution checkerboard technique based on the European Committee on Antimicrobial Susceptibility Testing (EUCAST) reference method for antifungal susceptibility testing. Selected isolates (A. nidulans, n = 10; A. niger, n = 15) were additionally evaluated by an agar diffusion assay using isavuconazole gradient concentration strips with or without colistin incorporated Roswell Parc Memorial Institute (RPMI) agar. Interpretation of the checkerboard results was done by the fractional inhibitory concentration index. Using the checkerboard method, combination isavuconazole-colistin was synergistic for 100% of the 15 A. nidulans isolates and for 60% of the 20 A. niger isolates. No interactions were found for any of the other isolates. By agar diffusion assay, minimal inhibitory concentrations (MICs) in combination decreased compared to isavuconazole alone for 92% of the isolates. No interactions were found for any A. nidulans isolates, but synergy was observed for 40% of the A. niger isolates. A poor essential agreement of EUCAST and gradient concentration strip MICs at ± 2 log2 dilutions with 0% was obtained. Antagonistic interactions were never observed regardless of the technique used.

Allicin reduces inflammation by regulating ROS/NLRP3 and autophagy in the context of A. fumigatus infection in mice

OBJECTIVES

Inhibitory effect of allicin with broad-spectrum antimicrobial activity on A. fumigatus and the regulation mechanism of inflammation and autophagy in vitro and in vivo.

METHODS

The corresponding concentration of allicin was prepared according to the needs of the experiment. In vitro, 2 ml 5 × 10⁴ of fungal spores suspension was added to the 6-well plate per hole, and different final concentrations of allicin (1 μl/ml, 2.5 μl/ml, 5 μl/ml, 10 μl/ml, 20 μl/ml, 30 μl/ml) were added. The fungal spores were stained by fluorescent dye SYTO 9 (green) every day, and the spore germination inhibition was detected by flow cytometry in different PH. RAW264.7 cells were cultured and stimulated by A. fumigatus spores for 3 h, then allicin solution was added. Then some cells were stained with ROS probe (green) and hochest33342 (blue). The effect of allicin on ROS was observed by fluorescence microscope. The other part of cells extracted protein from cell lysate and detected the effect of allicin on inflammatory factors and autophagy by Western-blotting. The green and red spots of RAW264.7 cells stably transfected with GFP-RFP-LC3 were observed by fluorescence microscopy. In vivo, A. fumigatus spore was injected intratracheally into mice, then allicin was injected intravenously at a concentration of 5 mg/kg/day for 7 consecutive days. The survival status, pulmonary fungal load and weight of mice was recorded continuously for 30 days and detected the changes of lung by pathological examination and immunohistochemistry.

RESULTS

In vitro, allicin significantly inhibited the spore germination of A. fumigatus within 24 h in a dose-dependent manner and it had a stable inhibition on the spore germination of A. fumigatus in acidic environment. Cell experiments showed that allicin inhibited intracellular spore germination by inhibiting ROS production, inflammation and autophagy. In the animal experiment, the survival rate and body weight of allicin injection group were higher than that of non injection group, while the spore load of lung was lower than that of non injection group (P < 0.05).

CONCLUSIONS

These results support that allicin reduces inflammation and autophagy resistance to A. fumigatus infection, It also provides a possible treatment for Aspergillus infectious diseases, i.e. early anti-inflammation, antibiotics or drugs that inhibit excessive autophagy.

One year prospective survey of azole resistance in Aspergillus fumigatus at a French cystic fibrosis reference centre: prevalence and mechanisms of resistance

BACKGROUND

Studies on Aspergillus fumigatus azole resistance in cystic fibrosis patients are scarce despite the fact that it is the most frequently isolated fungus from respiratory samples from these individuals.

OBJECTIVES

To evaluate resistance prevalence, investigate mechanisms of resistance and explore the relationship between resistant isolates by genotyping.

METHODS

We conducted a prospective 1 year study (from 1 January to 31 December 2015), based on the investigation of up to five colonies per sample from cystic fibrosis patients.

RESULTS

Twenty-three (6.5%) isolates among the 355 tested were resistant to at least one triazole drug, using the EUCAST reference method, leading to a prevalence of 6.8% (6/88 patients). Analysis of resistance mechanisms highlighted TR34/L98H (n = 10), TR46/Y121F/T289A (n = 1), WT cyp51A (n = 11) and F46Y/M172V/N248T/D255E/E427K (n = 1). No genotype was shared between patients.

CONCLUSIONS

This study showed a relatively stable resistance prevalence in comparison with the previous study conducted in 2010-11 (8%), although resistance mechanisms varied between the two studies.

Identification of Fungal Species and Detection of Azole-Resistance Mutations in the Aspergillus fumigatus cyp51A Gene at a South Korean Hospital

PURPOSE

With changing fungal epidemiology and azole resistance in Aspergillus species, identifying fungal species and susceptibility patterns is crucial to the management of aspergillosis and mucormycosis. The objectives of this study were to evaluate performance of panfungal polymerase chain reaction (PCR) assays on formalin-fixed paraffin embedded (FFPE) samples in the identification of fungal species and in the detection of azole-resistance mutations in the Aspergillus fumigatus cyp51A gene at a South Korean hospital.

MATERIALS AND METHODS

A total of 75 FFPE specimens with a histopathological diagnosis of aspergillosis or mucormycosis were identified during the 10-year study period (2006-2015). After deparaffinization and DNA extraction, panfungal PCR assays were conducted on FFPE samples for fungal species identification. The identified fungal species were compared with histopathological diagnosis. On samples identified as A. fumigatus, sequencing to identify frequent mutations in the cyp51A gene [tandem repeat 46 (TR46), L98H, and M220 alterations] that confer azole resistance was performed.

RESULTS

Specific fungal DNA was identified in 31 (41.3%) FFPE samples, and of these, 16 samples of specific fungal DNA were in accord with a histopathological diagnosis of aspergillosis or mucormycosis; 15 samples had discordant histopathology and PCR results. No azole-mediating cyp51A gene mutation was noted among nine cases of aspergillosis. Moreover, no cyp51A mutations were identified among three cases with history of prior azole use.

CONCLUSION

Panfungal PCR assay with FFPE samples may provide additional information of use to fungal species identification. No azole-resistance mediating mutations in the A. fumigatus cyp51A gene were identified among FFPE samples during study period.

Anti-fungal activity of a novel triazole, PC1244, against emerging azole-resistant Aspergillus fumigatus and other species of Aspergillus

Objectives

The growing emergence of azole-resistant Aspergillus fumigatus strains worldwide is a major concern for current systemic antifungal treatment. Here we report antifungal activities of a novel inhaled triazole, PC1244, against a collection of multi-azole-resistant A. fumigatus strains.

Methods

MICs of PC1244 were determined for A. fumigatus carrying TR₃₄/L98H (n = 81), TR₄₆/Y121F/T289A (n = 24), M220 (n = 6), G54 (n = 11), TR₅₃ (n = 1), TR₄₆³/Y121F/T289A (n = 2), G448S (n = 1), G432C (n = 1) and P216S (n = 1) resistance alleles originating from either India, the Netherlands or France. The effects of PC1244 were confirmed in an in vitro model of the human alveolus and in vivo in temporarily neutropenic, immunocompromised mice.

Results

PC1244 exhibited potent inhibition [geometric mean MIC (range), 1.0 mg/L (0.125 to >8 mg/L)] of growth of A. fumigatus strains carrying cyp51A gene mutations, showing much greater potency than voriconazole [15 mg/L (0.5 to >16 mg/L)], and an effect similar to those on other azole-susceptible Aspergillus spp. (Aspergillus flavus, Aspergillus terreus, Aspergillus tubingensis, Aspergillus nidulans, Aspergillus niger, Aspergillus nomius, Aspergillus tamarii) (0.18–1 mg/L). In TR₃₄/L98H and TR₄₆/Y121F/T289A A. fumigatus-infected in vitro human alveolus models, PC1244 achieved superior inhibition (IC₅₀, 0.25 and 0.34 mg/L, respectively) compared with that of voriconazole (IC₉₀, >3 mg/L and >10 mg/L, respectively). In vivo, once-daily intranasal administration of PC1244 (0.56–70 μg/mouse) to the A. fumigatus (AF91 with M220V)-infected mice reduced pulmonary fungal load and serum galactomannan more than intranasal posaconazole.

Conclusions

PC1244 has the potential to become a novel topical treatment of azole-resistant pulmonary aspergillosis.

A Collaborative Tale of Diagnosing and Treating Chronic Pulmonary Aspergillosis, from the Perspectives of Clinical Microbiologists, Surgical Pathologists, and Infectious Disease Clinicians

Chronic pulmonary aspergillosis (CPA) refers to a spectrum of Aspergillus-mediated disease that is associated with high morbidity and mortality, with its true prevalence vastly underestimated. The diagnosis of CPA includes characteristic radiographical findings in conjunction with persistent and systemic symptoms present for at least three months, and evidence of Aspergillus infection. Traditionally, Aspergillus infection has been confirmed through histopathology and microbiological studies, including fungal culture and serology, but these methodologies have limitations that are discussed in this review. The treatment of CPA requires an individualized approach and consideration of both medical and surgical options. Most Aspergillus species are considered susceptible to mold-active triazoles, echinocandins, and amphotericin B; however, antifungal resistance is emerging and well documented, demonstrating the need for novel therapies and antifungal susceptibility testing that correlates with clinical response. Here, we describe the clinical presentation, diagnosis, and treatment of CPA, with an emphasis on the strengths and pitfalls of diagnostic and treatment approaches, as well as future directions, including whole genome sequencing and metagenomic sequencing. The advancement of molecular technology enables rapid and precise species level identification, and the determination of molecular mechanisms of resistance, bridging the clinical infectious disease, anatomical pathology, microbiology, and molecular biology disciplines.

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.

New vinyl-1,2,4-triazole derivatives as antimicrobial agents: Synthesis, biological evaluation and molecular docking studies

1,2,4-Triazole is a very important scaffold in medicinal chemistry due to the wide spectrum of biological activities and mainly antifungal activity of 1,2,4-triazole derivatives. The main mechanism of antifungal action of the latter is inhibition of 14-alpha-demethylase enzyme (CYP51). The current study presents synthesis and evaluation of eight triazole derivatives for their antimicrobial activity. Docking studies to elucidate the mechanism of action were also performed. The designed compounds were synthesized using classical methods of organic synthesis. The in vivo evaluation of antimicrobial activity was performed by microdilution method. All tested compounds showed good antibacterial activity with MIC and MBC values ranging from 0.0002 to 0.0069 mM. Compound 2 h appeared to be the most active among all tested with MIC at 0.0002-0.0033 mM and MBC at 0.0004-0.0033 mM followed by compounds 2f and 2g. The most sensitive bacterium appeared to be Xanthomonas campestris while Erwinia amylovora was the most resistant. The evaluation of antifungal activity revealed that all compounds showed good antifungal activity with MIC values ranging from 0.02 mM to 0.52 mM and MFC from 0.03 mM to 0.52 mM better than reference drugs ketoconazole (MIC and MFC values at 0.28-1.88 mM and 0.38 mM to 2.82 mM respectively) and bifonazole (MIC and MFC values at 0.32-0.64 mM and 0.64-0.81 mM). The best antifungal activity is displayed by compound 2 h with MIC at 0.02-0.04 mM and MFC at 0.03-0.06 mM while compound 2a showed the lowest activity. The results showed that these compounds could be lead compounds in search for new potent antimicrobial agents. Docking studies confirmed experimental results.

Aspergillus fumigatus Transcription Factors Involved in the Caspofungin Paradoxical Effect

Aspergillus fumigatus, one of the most important human-pathogenic fungal species, is able to cause aspergillosis, a heterogeneous group of diseases that presents a wide range of clinical manifestations. Invasive pulmonary aspergillosis is the most serious pathology in terms of patient outcome and treatment, with a high mortality rate ranging from 50% to 95% primarily affecting immunocompromised patients. Azoles have been used for many years as the main antifungal agents to treat and prevent invasive aspergillosis. However, there were several reports of evolution of clinical azole resistance in the last decade. Caspofungin, a noncompetitive β-1,3-glucan synthase inhibitor, has been used against A. fumigatus, but it is fungistatic and is recommended as second-line therapy for invasive aspergillosis. More information about caspofungin tolerance and resistance is necessary in order to refine antifungal strategies that target the fungal cell wall. Here, we screened a transcription factor (TF) deletion library for TFs that can mediate caspofungin tolerance and resistance. We have identified 11 TFs that are important for caspofungin sensitivity and/or for the caspofungin paradoxical effect (CPE). These TFs encode proteins involved in the basal modulation of the RNA polymerase II initiation sites, calcium metabolism or cell wall remodeling, and mitochondrial respiratory function. The study of those genes regulated by TFs identified in this work will provide a better understanding of the signaling pathways that are important for caspofungin tolerance and resistance.

Aspergillus fumigatus is the leading cause of pulmonary fungal diseases. Azoles have been used for many years as the main antifungal agents to treat and prevent invasive aspergillosis. However, in the last 10 years there have been several reports of azole resistance in A. fumigatus and new strategies are needed to combat invasive aspergillosis. Caspofungin is effective against other human-pathogenic fungal species, but it is fungistatic only against A. fumigatus. Resistance to caspofungin in A. fumigatus has been linked to mutations in the fksA gene that encodes the target enzyme of the drug β-1,3-glucan synthase. However, tolerance of high caspofungin concentrations, a phenomenon known as the caspofungin paradoxical effect (CPE), is also important for subsequent adaptation and drug resistance evolution. Here, we identified and characterized the transcription factors involved in the response to CPE by screening an A. fumigatus library of 484 null transcription factors (TFs) in CPE drug concentrations. We identified 11 TFs that had reduced CPE and that encoded proteins involved in the basal modulation of the RNA polymerase II initiation sites, calcium metabolism, and cell wall remodeling. One of these TFs, FhdA, was important for mitochondrial respiratory function and iron metabolism. The ΔfhdA mutant showed decreased growth when exposed to Congo red or to high temperature. Transcriptome sequencing (RNA-seq) analysis and further experimental validation indicated that the ΔfhdA mutant showed diminished respiratory capacity, probably affecting several pathways related to the caspofungin tolerance and resistance. Our results provide the foundation to understand signaling pathways that are important for caspofungin tolerance and resistance.

Azole-Resistant COVID-19-Associated Pulmonary Aspergillosis in an Immunocompetent Host: A Case Report

COVID-19-associated pulmonary aspergillosis (CAPA) is a recently described disease entity affecting patients with severe pulmonary abnormalities treated in intensive care units. Delays in diagnosis contribute to a delayed start of antifungal therapy. In addition, the emergence of resistance to triazole antifungal agents puts emphasis on early surveillance for azole-resistant Aspergillus species. We present a patient with putative CAPA due to Aspergillus fumigatus with identification of a triazole-resistant isolate during therapy. We underline the challenges faced in the management of these cases, the importance of early diagnosis and need for surveillance given the emergence of triazole resistance.

High-Frequency Direct Detection of Triazole Resistance in Aspergillus fumigatus from Patients with Chronic Pulmonary Fungal Diseases in India

Aspergillosis due to azole-resistant Aspergillus fumigatus is a worldwide problem with major therapeutic implications. In patients with invasive aspergillosis, a low yield of fungal cultures results in underestimation of azole resistance. To detect azole resistance in A. fumigatus, we applied the AsperGenius^® Resistance multiplex real-time polymerase chain reaction (PCR) assay to detect TR₃₄/L98H, and TR₄₆/T289A/Y121F mutations and the AsperGenius^® G54/M220 RUO PCR assay to detect G54/M220 mutations directly in bronchoalveolar lavage (BAL) samples of 160 patients with chronic respiratory diseases in Delhi, India. Only 23% of samples were culture-positive compared to 83% positivity by A. fumigatus species PCR highlighting concerns about the low yield of cultures. Notably, 25% of BAL samples (33/160 patients) had azole resistance-associated mutation by direct detection using PCR assay. Detection of resistance-associated mutations was found mainly in 59% and 43% patients with chronic pulmonary aspergillosis (CPA) and allergic bronchopulmonary aspergillosis (ABPA), respectively. Overall, a G54 mutation, conferring itraconazole resistance, was the predominant finding in 87.5% and 67% of patients with CPA and ABPA, respectively. In culture-negative, PCR-positive samples, we detected azole-resistant mutations in 34% of BAL samples. Azole resistance in chronic Aspergillus diseases remains undiagnosed, warranting standardization of respiratory culture and inclusion of rapid techniques to detect resistance markers directly in respiratory samples.

Optimal management of acute kidney injury in critically ill patients with invasive fungal infections being treated with liposomal amphotericin B

Critically ill patients are at risk of developing both acute kidney injury (AKI) and invasive fungal infections (IFIs). Prompt and efficient treatment of the IFI is essential for the survival of the patient. This article examines three distinct clinical situations where liposomal amphotericin B, a broad-spectrum antifungal agent, was successfully used in the setting of AKI. The first was Aspergillus infection in a 63-year-old man with bleeding oesophageal varices related to advanced liver disease. The second was gastrointestinal mucormycosis in a 74-year-old man who developed a small bowel obstruction following an autologous stem cell transplant for mantle cell lymphoma. The third was a Fusarium infection in a 32-year-old woman on immunosuppression for a bilateral lung transplant for cystic fibrosis. In all three cases, liposomal amphotericin B was required for urgent management of the patient’s IFI. We discuss the rationale for treatment with a potentially nephrotoxic agent in this setting.

Antifungal Susceptibility Testing: Current Approaches

Although not as ubiquitous as antibacterial susceptibility testing, antifungal susceptibility testing (AFST) is a tool of increasing importance in clinical microbiology laboratories. The goal of AFST is to reliably produce MIC values that may be used to guide patient therapy, inform epidemiological studies, and track rates of antifungal drug resistance. There are three methods that have been standardized by standards development organizations: broth dilution, disk diffusion, and azole agar screening for Aspergillus Other commonly used methods include gradient diffusion and the use of rapid automated instruments. Novel methodologies for susceptibility testing are in development. It is important for laboratories to consider not only the method of testing but also the interpretation (or lack thereof) of in vitro data.

An overview of the available treatments for chronic cavitary pulmonary aspergillosis

INTRODUCTION

Chronic pulmonary aspergillosis (CPA) is a chronic lung infection caused by Aspergillus fumigatus, that complicates structural lung diseases. Of the different types of CPA, chronic cavitary pulmonary aspergillosis (CCPA) is the most common form. The mainstay of treatment of CCPA is oral triazoles. However, many gaps exist in clinical decision-making about the agent of choice, the duration, and the assessment of treatment response.

AREAS COVERED

We discuss the approach to diagnosis and treatment of CCPA. We have searched the PubMed and EmBase databases (from inception till 31 October 2019) to identify studies describing the use of anti-fungal agents in CCPA.

EXPERT OPINION

Treatment for CCPA should be initiated with oral itraconazole for at least six months. In case of poor response or intolerance to itraconazole, voriconazole should be considered. Intravenous agents, including amphotericin B and echinocandins, may be used in those with either treatment failure or those who are intolerant to oral antifungal agents. Posaconazole and isavuconazole may be used as salvage therapy due to a better pharmacokinetic/pharmacodynamic profile of the former and reduced drug-drug interactions with the latter.

A 23 bp cyp51A Promoter Deletion Associated With Voriconazole Resistance in Clinical and Environmental Isolates of Neocosmospora keratoplastica

In the fungal pathogen Aspergillus fumigatus, resistance to azole antifungals is often linked to mutations in CYP51A, a gene that encodes the azole antifungal drug target lanosterol 14α-demethylase. The aim of this study was to investigate whether similar changes could be associated with azole resistance in a Malaysian Fusarium solani species complex (FSSC) isolate collection. Most (11 of 15) clinical FSSC isolates were Neocosmospora keratoplastica and the majority (6 of 10) of environmental isolates were Neocosmospora suttoniana strains. All 25 FSSC isolates had high minimum inhibitory concentrations (MICs) for itraconazole and posaconazole, low MICs for amphotericin B, and various (1 to >32 mg/l) voriconazole susceptibilities. There was a tight association between a 23 bp CYP51A promoter deletion and high (>32 mg/l) voriconazole MICs; of 19 FSSC strains sequenced, nine isolates had voriconazole MICs > 32 mg/l, and they all contained the 23 bp CYP51A promoter deletion, although it was absent in the ten remaining isolates with low (≤12 mg/l) voriconazole MICs. Surprisingly, this association between voriconazole resistance and the 23 bp CYP51A promoter deletion held true across species boundaries. It was randomly distributed within and across species boundaries and both types of FSSC isolates were found among environmental and clinical isolates. Three randomly selected N. keratoplastica isolates with low (≤8 mg/l) voriconazole MICs had significantly lower (1.3–7.5 times) CYP51A mRNA expression levels than three randomly selected N. keratoplastica isolates with high (>32 mg/l) voriconazole MICs. CYP51A expression levels, however, were equally strongly induced (~6,500-fold) by voriconazole in two representative strains reaching levels, after 80 min of induction, that were comparable to those of CYP51B. Our results suggest that FSSC isolates with high voriconazole MICs have a 23 bp CYP51A promoter deletion that provides a potentially useful marker for voriconazole resistance in FSSC isolates. Early detection of possible voriconazole resistance is critical for choosing the correct treatment option for patients with invasive fusariosis.

Azole-resistant Aspergillus and Echinocandin-resistant Candida - What are the treatment options?

Purpose of Review

This review summarizes current treatment options for echinocandin-resistant Candida spp. (ERC) and azole-resistant Aspergillus fumigatus (ARAF), emphasizing recent in vitro/in vivo data, clinical reports, and consensus statements.

Recent Findings

Advances in ERC and ARAF treatment are limited to specific antifungal combinations and dose optimization but remain reliant on amphotericin products. Although novel antifungals may provide breakthroughs in the treatment of resistant fungi, these agents are not yet available. Early identification and appropriate treatment remain a paramount, albeit elusive, task.

Summary

When either ERC or ARAF are suspected or proven, amphotericin products remain the cornerstone of initial therapy. For ERC, azoles are de-escalation options for susceptible isolates in stable patients to avoid amphotericin toxicities. Although combination echinocandin with high-dose salvage posaconazole or isavuconazole may be attempted in ARAF, it requires careful consideration following patient stabilization. Future research defining optimal therapies and early identification of ERC and ARAF is of extreme importance.

A Simple Method To Detect Point Mutations in Aspergillus fumigatus cyp51A Gene Using a Surveyor Nuclease Assay

One of the main mechanisms of azole resistance of Aspergillus fumigatus is thought to be a reduction in the drug's affinity for the target molecule, Cyp51A, due to its amino acid mutation(s). It is known that the azole resistance pattern is closely related to the mutation site(s) of the molecule. In this study, we tried to develop a simple and rapid detection method for cyp51A mutations using the endonuclease Surveyor nuclease. The Surveyor nuclease assay was verified using several azole-resistant strains of A. fumigatus that possess point mutations in Cyp51A. For validation of the Surveyor nuclease assay, blind tests were conducted using 48 strains of A. fumigatus (17 azole-resistant and 31 azole-susceptible strains). The Surveyor nuclease assay could rapidly detect cyp51A mutations with one primer set. Also, all the tested strains harboring different cyp51A single point mutations could be clearly distinguished from the wild type. The Surveyor nuclease assay is a simple method that can detect cyp51A mutations rapidly.

First azole-resistant Aspergillus fumigatus isolates with the environmental TR46 /Y121F/T289A mutation in Iran

Background

Azole resistance in Aspergillus fumigatus is an emerging problem and reported from all continents. As triazole antifungals are the mainstay of therapy in the management of invasive aspergillosis, azole‐resistant A fumigatus has become a major medical concern and with complicated clinical management.

Objective

Screening of environmental presence of azole‐resistant A fumigatus in Iran.

Methods

Compost from Northern Iran, collected between 2017 and 2018, was screened for the presence of azole‐resistant A fumigatus with azole‐containing agar. Phenotypic MICs were obtained from selected, molecularly confirmed isolates. cyp51A gene sequencing and genotyping of azole‐resistant isolates were done.

Results

Among 300 compost samples, three A fumigatus isolates had high voriconazole MICs (≥16 mg/L) and harboured the TR₄₆/Y121F/T289A mutation in the cyp51A gene. Microsatellite typing of these isolates showed that two strains had the same allele across all nine examined microsatellite loci and were genotypically related to Indian azole‐resistant strains. The other isolate had a different genotype.

Conclusion

This is the first report of A fumigatus with TR₄₆/Y121F/T289A mutation from the region. Monitoring and surveillance of antifungal susceptibility of clinical A fumigatus is warranted in Iran and elsewhere in the region.

Comparison of the MICs Obtained by Gradient Concentration Strip and EUCAST Methods for Four Azole Drugs and Amphotericin B against Azole-Susceptible and -Resistant Aspergillus Section Fumigati Clinical Isolates

Reference methods used to assess the drug susceptibilities of Aspergillus fumigatus isolates consisted of EUCAST and CLSI standardized broth microdilution techniques. Considering the increasing rate and the potential impact on the clinical outcome of azole resistance in A. fumigatus, more suitable techniques for routine testing are needed. The gradient concentration strip (GCS) method has been favorably evaluated for yeast testing. The aim of this study was to compare the CGS test with EUCAST broth microdilution for amphotericin B (AMB), posaconazole (PCZ), itraconazole (ITZ), voriconazole (VRZ), and isavuconazole (ISA). A total of 121 Aspergillus section Fumigati strains were collected, including 24 A. fumigatus sensu stricto strains that were resistant to at least one azole drug. MICs were determined using GCS and EUCAST methods. Essential agreement between the 2 methods was considered when MICs fell within ±1 dilution or ±2 dilutions of the 2-fold dilution scale. Categorical agreement was defined as the percentage of strains classified in the same category (susceptible, intermediate, or resistant) with both methods. Essential agreements with ±1 dilution and ±2 dilutions were 96.7, 93.4, 90.0, 89.3, and 95% and 100, 99.2, 100, 97.5, and 100% for AMB, PCZ, ITZ, VRZ, and ISA, respectively. Categorical agreements were 94.3, 86.1, 89.3, and 88.5% for AMB, PCZ, ITZ, and VRZ, respectively. Detection of resistance was missed with the GCS for one strain (4.1%) for PCZ and for 2 strains (8.3%) for ISA. Determination of ITZ MICs using the GCS allowed the detection of 91.7% of azole-resistant strains. The GCS test appears to be a valuable method for screening azole-resistant A. fumigatus clinical isolates.

Hope on the Horizon: Novel Fungal Treatments in Development

The treatment of invasive fungal infections remains challenging due to limitations in currently available antifungal therapies including toxicity, interactions, restricted routes of administration, and drug resistance. This review focuses on novel therapies in clinical development, including drugs and a device. These drugs have novel mechanisms of action to overcome resistance, and some offer new formulations providing distinct advantages over current therapies to improve safety profiles and reduce interactions. Among agents that target the cell wall, 2 glucan synthesis inhibitors are discussed (rezafungin and ibrexafungerp), as well as fosmanogepix and nikkomycin Z. Agents that target the cell membrane include 3 fourth-generation azoles, oral encochleated amphotericin B, and aureobasidin A. Among agents with intracellular targets, we will review olorofim, VL-2397, T-2307, AR-12, and MGCD290. In addition, we will describe neurapheresis, a device used as adjunctive therapy for cryptococcosis. With a field full of novel treatments for fungal infections, the future looks promising.

Uncovering New Mutations Conferring Azole Resistance in the Aspergillus fumigatus cyp51A Gene

The opportunistic pathogen Aspergillus fumigatus has developed worldwide resistance to azoles largely through mutations in cytochromeP450 enzyme Cyp51. In this study, we indicated that in vitro azole situation results in emergence of azole-resistant mutations. There are previously identified azole-resistant cyp51A mutations (M220K, M220I, M220R, G54E and G54W mutations) and we successfully identified in this study two new mutations (N248K/V436A, Y433N substitution) conferring azole resistance among 18 independent stable azole-resistant isolates. The Galleria mellonella model of A. fumigatus infection experiment verified that Cyp51A mutations N248K/V436A and Y433N reduce efficacy of azole therapy. In addition, a predicted Cyp51A 3D structural model suggested that Y433N mutation causes the reduced affinities between drug target Cyp51A and azole antifungals. This study suggests that drug selection pressure make it possible to isolate unidentified cyp51A mutations conferring azole resistance in A. fumigatus.

Prospective multicenter surveillance of clinically isolated Aspergillus species revealed azole-resistant Aspergillus fumigatus isolates with TR34/L98H mutation in the Kyoto and Shiga regions of Japan

The prevalence of azole-resistant Aspergillus fumigatus (ARAF) in Japan is unclear. We aimed to investigate the epidemiology of clinically isolated Aspergillus species and the frequency of azole resistance in Aspergillus species, particularly Aspergillus fumigatus, in the Kyoto and Shiga regions of Japan. Strains of clinically isolated Aspergillus species were prospectively collected from nine acute care hospitals. Species identification was performed by DNA sequence analysis, and all strains were subjected to antifungal susceptibility testing. Sequencing of the Aspergillus cyp51A gene and promoter region and genotyping by short tandem repeats were performed for ARAF isolates. A total of 149 strains were collected, and 130 strains were included for the subsequent analysis after the exclusion of duplicate isolates. The most commonly isolated species was Aspergillus fumigatus, accounting for 43.1% (56 isolates) overall, and seven (12.7%) of 55 strains of A. fumigatus were azole-resistant. Azole-resistance of other Aspergillus species were also found that two (22.2%) of nine strains of A. tubingensis and two (28.6%) of seven strains of A. flavus were azole-resistant. DNA sequence analysis of the ARAF strains revealed that two carried the cyp51A TR34/L98H mutation, one carried G448S, one carried M220I, and three had no relevant mutations (wild type). Genotyping and phylogenetic analyses showed that the TR34/L98H strains were clustered with the strains from the Netherlands and France. These data suggest the emergence of ARAF with TR34/L98H in Japan, and continuous surveillance will be important to identify trends in resistance.

Mutation in cyp51A and high expression of efflux pump gene of Aspergillus fumigatus induced by propiconazole in liquid medium and soil

Triazole resistance in Aspergillus fumigatus is a major cause of clinical inefficacy in the treatment of invasive aspergillosis (IA). The hypothesis that triazole fungicides have driven the development of resistance in A. fumigatus has garnered substantial attention due to the similar structure and global detection of antifungal resistant A. fumigatus (ARAF) isolates in the soil. However, there is little evidence linking the application of triazole fungicides to the emergence of ARAF in the soil. This study was conducted to test if the resistance in A. fumigatus and its associated mutations in cyp51A could be induced by propiconazole in liquid medium and soil. The results indicate that propiconazole can induce resistance by alteration of G138S in cyp51A, and the overexpression of cyp51A, AfuMDR3 and AfuMDR4. G138S in cyp51A was first detected in the soil and associated with resistance. The emergence of the ARAFs in the soil may depends upon the level of propiconazole, and the number of ARAFs in soil treated with propiconazole at 2- and 5-fold dose was much greater than those in soil treated at the recommended dosage. The current data indicate that propiconazole can induce triazole resistance in A. fumigatus and should be applied for agricultural purposes at levels at or below the recommended dosage to avoid the emergence of ARAF in the soil.

Aspergillus fumigatus and Aspergillosis in 2019

Aspergillus fumigatus is a saprotrophic fungus; its primary habitat is the soil. In its ecological niche, the fungus has learned how to adapt and proliferate in hostile environments. This capacity has helped the fungus to resist and survive against human host defenses and, further, to be responsible for one of the most devastating lung infections in terms of morbidity and mortality. In this review, we will provide (i) a description of the biological cycle of A. fumigatus; (ii) a historical perspective of the spectrum of aspergillus disease and the current epidemiological status of these infections; (iii) an analysis of the modes of immune response against Aspergillus in immunocompetent and immunocompromised patients; (iv) an understanding of the pathways responsible for fungal virulence and their host molecular targets, with a specific focus on the cell wall; (v) the current status of the diagnosis of different clinical syndromes; and (vi) an overview of the available antifungal armamentarium and the therapeutic strategies in the clinical context. In addition, the emergence of new concepts, such as nutritional immunity and the integration and rewiring of multiple fungal metabolic activities occurring during lung invasion, has helped us to redefine the opportunistic pathogenesis of A. fumigatus.

First-in-Human Phase 1 Study To Assess Safety, Tolerability, and Pharmacokinetics of a Novel Antifungal Drug, VL-2397, in Healthy Adults

VL-2397 is an antifungal drug with a novel mechanism of action, rapid fungicidal in vitro activity, and potent in vivo activity against Aspergillus fumigatus, including azole-resistant strains. VL2397-101, a phase 1 first-in-human, randomized, double-blind, placebo-controlled dose-escalation study, was conducted in healthy adults to determine the safety, tolerability, and pharmacokinetics (PK) of single and multiple ascending intravenous (i.v.) doses of VL-2397. All dosing cohorts were fully enrolled; all subjects completed the safety follow-up. A safety committee reviewed the safety data for each dosing cohort prior to recommending the initiation of each subsequent cohort. No serious adverse events (SAEs) occurred; the majority of treatment-emergent adverse events (TEAEs) were mild and self-limited. The most common drug-related TEAEs were infusion site reactions. No clinically concerning trends were noted in vital signs, electrocardiograms, physical examinations, or safety laboratory results. Following single infusions of VL-2397, the overall and maximum exposures rose less than proportionally with increasing doses from 3 mg to 1,200 mg as indicated by area under the concentration-time curve over 24 h (AUC24) and maximum concentration (Cmax). No signs of VL-2397 accumulation were observed following i.v. infusions of 300, 600, and 1,200 mg every 24 h (q24h) for 7 days. Renal elimination played a major role in total body clearance, with up to 47% of unmetabolized drug in urine 24 h after administration at single doses of >30 mg. Overall, VL-2397 dosing in the study appeared to be safe and well tolerated in the healthy subjects. The safety profile, consistent PK, and lack of drug accumulation support further development of VL-2397 in patients with invasive aspergillosis.

Recent trends in the epidemiology, diagnosis, treatment, and mechanisms of resistance in clinical Aspergillus species: A general review with a special focus on the Middle Eastern and North African region

Globally, more than billion people suffer from fungal infections each year. The early diagnosis of aspergillosis is mandatory for successful treatment outcome. As careful testing takes time, epidemiological surveillance is crucial to guide individual patient therapy and to promote a high standard of health care. In this paper, we first present current trends in the epidemiology and antifungal susceptibility patterns of Aspergillus spp. in Middle Eastern and North African (MENA) countries in order to support infectious disease specialists and health workforces in this geographic area to treat adequately patients with aspergillosis. Then we discuss the existing literature data regarding the available diagnostic tools and antifungal resistance mechanisms of Aspergillus spp. Although a limited number of studies were reviewed here, the currently available data show that Aspergillus infections are not negligible in the MENA region, and that the emergence of antifungal resistance is a growing health issue, especially among immunocompromised patients.

cyp51A Mutations, Extrolite Profiles, and Antifungal Susceptibility in Clinical and Environmental Isolates of the Aspergillus viridinutans Species Complex

The past decade has seen an increase in aspergillosis in humans and animals due to Aspergillus viridinutans species complex members. Azole resistance is common to these infections, carrying a poor prognosis. cyp51A gene mutations are the main cause of acquired azole resistance in Aspergillus fumigatus. This study aimed to determine if the azole-resistant phenotype in A. viridinutans complex members is associated with cyp51A mutations or extrolite profiles.

The past decade has seen an increase in aspergillosis in humans and animals due to Aspergillus viridinutans species complex members. Azole resistance is common to these infections, carrying a poor prognosis. cyp51A gene mutations are the main cause of acquired azole resistance in Aspergillus fumigatus. This study aimed to determine if the azole-resistant phenotype in A. viridinutans complex members is associated with cyp51A mutations or extrolite profiles. The cyp51A gene of clinical and environmental isolates was amplified using novel primers, antifungal susceptibility was tested using the Clinical and Laboratory Standards Institute methodology, and extrolite profiling was performed using agar plug extraction. Very high azole MICs were detected in 84% of the isolates (31/37). The MICs of the newer antifungals luliconazole and olorofim (F901318) were low for all isolates. cyp51A sequences revealed 113 nonsynonymous mutations compared to the sequence of wild-type A. fumigatus. M172A/V and D255G, previously associated with A. fumigatus azole resistance, were common among all isolates but were not correlated with azole MICs. Two environmental isolates with nonsusceptibility to itraconazole and high MICs of voriconazole and isavuconazole harbored G138C, previously associated with azole-resistant A. fumigatus. Some novel mutations were identified only among isolates with high azole MICs. However, cyp51A homology modeling did not cause a significant protein structure change for these mutations. There was no correlation between extrolite patterns and susceptibility. For A. viridinutans complex isolates, cyp51A mutations and the extrolites that they produced were not major causes of antifungal resistance. Luliconazole and olorofim show promise for treating azole-resistant infections caused by these cryptic species.

Surveillance for azole resistance in clinical and environmental isolates of Aspergillus fumigatus in Australia and cyp51A homology modelling of azole-resistant isolates

Background

The prevalence of azole resistance in Aspergillus fumigatus is uncertain in Australia. Azole exposure may select for resistance. We investigated the frequency of azole resistance in a large number of clinical and environmental isolates.

Methods

A. fumigatus isolates [148 human, 21 animal and 185 environmental strains from air (n = 6) and azole-exposed (n = 64) or azole-naive (n = 115) environments] were screened for azole resistance using the VIPcheck™ system. MICs were determined using the Sensititre™ YeastOne YO10 assay. Sequencing of the Aspergillus cyp51A gene and promoter region was performed for azole-resistant isolates, and cyp51A homology protein modelling undertaken.

Results

Non-WT MICs/MICs at the epidemiological cut-off value of one or more azoles were observed for 3/148 (2%) human isolates but not amongst animal, or environmental, isolates. All three isolates grew on at least one azole-supplemented well based on VIPcheck™ screening. For isolates 9 and 32, the itraconazole and posaconazole MICs were 1 mg/L (voriconazole MICs 0.12 mg/L); isolate 129 had itraconazole, posaconazole and voriconazole MICs of >16, 1 and 8 mg/L, respectively. Soil isolates from azole-exposed and azole-naive environments had similar geometric mean MICs of itraconazole, posaconazole and voriconazole (P > 0.05). A G54R mutation was identified in the isolates exhibiting itraconazole and posaconazole resistance, and the TR34/L98H mutation in the pan-azole-resistant isolate. cyp51A modelling predicted that the G54R mutation would prevent binding of itraconazole and posaconazole to the haem complex.

Conclusions

Azole resistance is uncommon in Australian clinical and environmental A. fumigatus isolates; further surveillance is indicated.

Bioactive Peptides Against Fungal Biofilms

Infections caused by invasive fungal biofilms have been widely associated with high morbidity and mortality rates, mainly due to the advent of antibiotic resistance. Moreover, fungal biofilms impose an additional challenge, leading to multidrug resistance. This fact, along with the contamination of medical devices and the limited number of effective antifungal agents available on the market, demonstrates the importance of finding novel drug candidates targeting pathogenic fungal cells and biofilms. In this context, an alternative strategy is the use of antifungal peptides (AFPs) against fungal biofilms. AFPs are considered a group of bioactive molecules with broad-spectrum activities and multiple mechanisms of action that have been widely used as template molecules for drug design strategies aiming at greater specificity and biological efficacy. Among the AFP classes most studied in the context of fungal biofilms, defensins, cathelicidins and histatins have been described. AFPs can also act by preventing the formation of fungal biofilms and eradicating preformed biofilms through mechanisms associated with cell wall perturbation, inhibition of planktonic fungal cells’ adhesion onto surfaces, gene regulation and generation of reactive oxygen species (ROS). Thus, considering the critical scenario imposed by fungal biofilms and associated infections and the application of AFPs as a possible treatment, this review will focus on the most effective AFPs described to date, with a core focus on antibiofilm peptides, as well as their efficacy in vivo, application on surfaces and proposed mechanisms of action.

Increased Efficacy of Oral Fixed-Dose Combination of Amphotericin B and AHCC® Natural Adjuvant against Aspergillosis

Invasive pulmonary aspergillosis represents one of the most serious fungal infections among immunocompromised patients. In this study, we aimed to analyze the in vivo efficacy of prophylactic oral amphotericin B (AMB) encapsulated in modified chitosan-nanoparticles (Nanomerics’ Molecular Envelope Technology (MET)) supplemented with a standardized extract of cultured Lentinula edodes mycelia (AHCC^®) in a murine model of pulmonary aspergillosis. We determined fungal burden and survival of mice and additionally, we carried out a cytokine analysis in an attempt to understand the immunomodulation of the extract. Our results evidenced equivalent efficacy between orally administered AMB-MET and the intravenous liposomal AMB marketed formulation. Addition of the AHCC^® supplement significantly improved efficacy in terms of burden reduction and survival increase of both oral and intravenous AMB therapies compared to the untreated control group. Moreover, a protective effect of the extract was observed in terms of weight loss. Regarding the cytokine profiles, the Th1 immune response was stimulated in treated animals when compared to the control group. This response was marked by an enhancement in the MCP-1, GM-CSF, VEGF, RANTES and IL-17 levels and a decrease in the IL-6, a biomarker related to the severity of the infection.

Genomic perspective of triazole resistance in clinical and environmental Aspergillus fumigatus isolates without cyp51A mutations

Aspergillus fumigatus is the most common etiologic agent of primarily all clinical manifestations of aspergillosis. A steady increase in the number of azole resistant A. fumigatus (ARAF) isolates from environment and clinical samples leading to therapeutic failures in clinical settings have alarmed the mycologists and clinicians worldwide. Although mutations in azole target cyp51A gene have been implicated in conferring azole resistance in A. fumigatus, recent studies have demonstrated occurrence of azole resistant strains without cyp51A mutations. In this study, next generation sequencing techniques and the expression profiling of transporter genes with single nucleotide polymorphisms (SNPs) in clinical and environmental ARAF isolates with (G54E) and without known cyp51A mutations was undertaken to understand the genetic background and role of transporters in azole resistance. The raw reads of four ARAF strains when mapped to Af293 reference genome (>100X depth) covered at least 93.1% of the reference genome. Among all four strains, a total of 212,711 SNPs was identified with 37,829 were common in at least two isolates. The expression analysis suggested the overexpression of MFS transporter, namely, mfsC in all ARAF isolates. None of the resistant strain showed significant upregulation of cyp51A and cyp51B gene. On the other hand, abcD was upregulated (5-fold) in the isolates with cyp 51A mutation (G54E). The whole genome sequence analysis showed the presence of two previously described amino acid substitutions S269F and F390Y in HMG1 gene in a clinical panazole resistant strain without cyp51A mutations. These mutations have been previously associated with azole resistance in A. fumigatus strains without cyp51A mutations. Further, several punctual mutations and a large-segment deletion among different strains were observed suggesting the involvement of resistance mechanisms other than cyp51A.

An Omics Approach to Diagnosing or Investigating Fungal Keratitis

Fungal keratitis (FK) is one of the most severe corneal infectious diseases. FK often leads to poor visual prognosis and thus requires accurate diagnosis. Conventional approaches, including clinical diagnoses, smears, and cultures, often fail to provide reliable diagnostic value. Omics approaches, such as those using genomic, metagenomic, and tear proteomic data sources, provide promising features for improving the diagnosis and monitoring the progression of FK. Genomic approaches are based mainly on detecting amplicons of ribosomal RNA genes, and internal transcribed spacers are gradually gaining popularity in clinical practices. A metagenomic approach based on 16S rRNA genes may help monitor the dynamic change of conjunctival microbiota associated with an FK event, whereas that based on shot-gun and 18S rRNA target enrichment sequencing could have the potential to diagnose FK using clinical samples. A tear proteomic approach may provide comprehensive information about ocular surface defense and injury during FK. Representative up- and down-regulated proteins during FK could also be used as biomarkers to determine the clinical course and develop a treatment strategy in different stages of FK. Consequently, a personalized tear proteomic approach will soon play a key role in FK management.

In Vitro Activity of APX001A (Manogepix) and Comparator Agents against 1,706 Fungal Isolates Collected during an International Surveillance Program in 2017

Current antifungal agents cover a majority of opportunistic fungal pathogens; however, breakthrough invasive fungal infections continue to occur and increasingly involve relatively uncommon yeasts and molds, which often exhibit decreased susceptibility. APX001A (manogepix) is a first-in-class small-molecule inhibitor of the conserved fungal Gwt1 protein. This enzyme is required for acylation of inositol during glycosylphosphatidylinositol anchor biosynthesis. APX001A is active against the major fungal pathogens, i.e., Candida (except Candida krusei), Aspergillus, and hard-to-treat molds, including Fusarium and Scedosporium In this study, we tested APX001A and comparators against 1,706 contemporary clinical fungal isolates collected in 2017 from 68 medical centers in North America (37.3%), Europe (43.4%), the Asia-Pacific region (12.7%), or Latin America (6.6%). Among the isolates tested, 78.5% were Candida spp., 3.9% were non-Candida yeasts, including 30 (1.8%) Cryptococcus neoformans var. grubii isolates, 14.7% were Aspergillus spp., and 2.9% were other molds. All isolates were tested by CLSI reference broth microdilution. APX001A (MIC₅₀, 0.008 μg/ml; MIC₉₀, 0.06 μg/ml) was the most active agent tested against Candida sp. isolates; corresponding anidulafungin, micafungin, and fluconazole MIC₉₀ values were 16- to 64-fold higher. Similarly, APX001A (MIC₅₀, 0.25 μg/ml; MIC₉₀, 0.5 μg/ml) was ≥8-fold more active than anidulafungin, micafungin, and fluconazole against C. neoformans var. grubii Against Aspergillus spp., AXP001A (50% minimal effective concentration [MEC₅₀], 0.015 μg/ml; MEC₉₀, 0.03 μg/ml) was comparable in activity to anidulafungin and micafungin. Aspergillus isolates (>98%) exhibited a wild-type phenotype for the mold-active triazoles (itraconazole, posaconazole, and voriconazole). APX001A was highly active against uncommon species of Candida, non-Candida yeasts, and rare molds, including 11 isolates of Scedosporium spp. (MEC values, 0.015 to 0.06 μg/ml). APX001A demonstrated potent in vitro activity against recent fungal isolates, including echinocandin- and fluconazole-resistant strains. The extended spectrum of APX001A was also notable for its potency against many less common but antifungal-resistant strains. Further studies are in progress to evaluate the clinical utility of the methyl phosphate prodrug, APX001, in difficult-to-treat resistant fungal infections.

Facilitators of adaptation and antifungal resistance mechanisms in clinically relevant fungi

Opportunistic fungal pathogens can cause a diverse range of diseases in humans. The increasing rate of fungal infections caused by strains that are resistant to commonly used antifungals results in difficulty to treat diseases, with accompanying high mortality rates. Existing and newly emerging molecular resistance mechanisms rapidly spread in fungal populations and need to be monitored. Fungi exhibit a diversity of mechanisms to maintain physiological resilience and create genetic variation; processes which eventually lead to the selection and spread of resistant fungal pathogens. To prevent and anticipate this dispersion, the role of evolutionary factors that drive fungal adaptation should be investigated. In this review, we provide an overview of resistance mechanisms against commonly used antifungal compounds in the clinic and for which fungal resistance has been reported. Furthermore, we aim to summarize and elucidate potent generators of genetic variability across the fungal kingdom that aid adaptation to stressful environments. This knowledge can lead to recognizing potential niches that facilitate fast resistance development and can provide leads for new management strategies to battle the emerging resistant populations in the clinic and the environment.

Invasive Aspergillosis by Aspergillus flavus: Epidemiology, Diagnosis, Antifungal Resistance, and Management

Aspergillus flavus is the second most common etiological agent of invasive aspergillosis (IA) after A. fumigatus. However, most literature describes IA in relation to A. fumigatus or together with other Aspergillus species. Certain differences exist in IA caused by A. flavus and A. fumigatus and studies on A. flavus infections are increasing. Hence, we performed a comprehensive updated review on IA due to A. flavus. A. flavus is the cause of a broad spectrum of human diseases predominantly in Asia, the Middle East, and Africa possibly due to its ability to survive better in hot and arid climatic conditions compared to other Aspergillus spp. Worldwide, ~10% of cases of bronchopulmonary aspergillosis are caused by A. flavus. Outbreaks have usually been associated with construction activities as invasive pulmonary aspergillosis in immunocompromised patients and cutaneous, subcutaneous, and mucosal forms in immunocompetent individuals. Multilocus microsatellite typing is well standardized to differentiate A. flavus isolates into different clades. A. flavus is intrinsically resistant to polyenes. In contrast to A. fumigatus, triazole resistance infrequently occurs in A. flavus and is associated with mutations in the cyp51C gene. Overexpression of efflux pumps in non-wildtype strains lacking mutations in the cyp51 gene can also lead to high voriconazole minimum inhibitory concentrations. Voriconazole remains the drug of choice for treatment, and amphotericin B should be avoided. Primary therapy with echinocandins is not the first choice but the combination with voriconazole or as monotherapy may be used when the azoles and amphotericin B are contraindicated.

[Invasive aspergillosis in the patient with oncohematologic disease]

Invasive aspergillosis is the most common invasive fungal infection in patients with acute hematological malignancies or treated with hematopoietic stem cell transplantation due to the marked alteration of the physiological mechanisms of antifungal immunity that takes place in these situations. For this reason, antifungal prophylaxis has a relevant role in these patients. The introduction of new antifungal agents has motivated the updating of recommendations for prophylaxis and treatment in different guidelines. The objectives of this chapter are a brief review of the mechanisms of immunity against fungi, the definition of risk for developing an invasive fungal infection and an update of the prophylaxis recommendations and treatment of invasive aspergillosis in the group of patients with hematological diseases.

New Insights into the Cyp51 Contribution to Azole Resistance in Aspergillus Section Nigri

Invasive aspergillosis (IA) is a severe condition mainly caused by Aspergillus fumigatus, although other species of the genus, such as section Nigri members, can also be involved. Voriconazole (VRC) is the recommended treatment for IA; however, the prevalence of azole-resistant Aspergillus isolates has alarmingly increased in recent years, and the underlying resistance mechanisms in non-fumigatus species remain unclear. We have determined the in vitro susceptibility of 36 strains from section Nigri to VRC, posaconazole (POS), and itraconazole (ITC), and we have explored the role of Cyp51A and Cyp51B, both targets of azoles, in azole resistance. The three drugs were highly active; POS displayed the best in vitro activity, while ITC and VRC showed MICs above the established epidemiological cutoff values in 9 and 16% of the strains, respectively. Furthermore, expression studies of cyp51A and cyp51B in control condition and after VRC exposure were performed in 14 strains with different VRC susceptibility. We found higher transcription of cyp51A, which was upregulated upon VRC exposure, but no correlation between MICs and cyp51 transcription levels was observed. In addition, cyp51A sequence analyses revealed nonsynonymous mutations present in both, wild-type and non-wild-type strains of A. niger and A. tubingensis Nevertheless, a few mutations were exclusively present in non-wild-type A. tubingensis strains. Altogether, our results suggest that azole resistance in section Nigri is not clearly explained by Cyp51A protein alteration or by cyp51 gene upregulation, which indicates that other mechanisms might be involved.

Extended Dosing Regimens for Fungal Prophylaxis

Invasive fungal diseases carry high morbidity and mortality in patients undergoing chemotherapy for hematological malignancies or allogeneic hematopoietic stem cell transplantation. In order to prevent these life-threatening infections, antifungal chemoprophylaxis plays an important role in daily clinical practice. Broad-spectrum antifungal triazoles are widely used but exhibit disadvantages such as relevant drug-drug interactions. Therefore, amphotericin B products or echinocandins can be an alternative in selected patient populations. As these compounds are available as intravenous formulations only, there is growing interest in extended dosing regimens. Although not approved for these agents, this strategy is a rational option, as these compounds have properties suitable for this strategy, including dose-proportional pharmacokinetics, prolonged elimination half-life, and a large therapeutic window. As the use of extended dosing regimens in antifungal prophylaxis is expanding in clinical practice, we reviewed the pharmacokinetic and pharmacodynamic rationale for this strategy, animal model data, dose escalation studies, and clinical trials supporting this concept.