Azole-resistant and -susceptible Aspergillus fumigatus isolates show comparable fitness and azole treatment outcome in immunocompetent mice

Efficacy of Inhaled N-Chlorotaurine in a Mouse Model of Lichtheimia corymbifera and Aspergillus fumigatus Pneumonia

N-chlorotaurine (NCT) can be used topically as a well-tolerated anti-infective at different body sites. The aim of this study was to investigate the efficacy of inhaled NCT in a mouse model of fungal pneumonia. Specific pathogen-free female C57BL/6JRj seven-week-old mice were immune-suppressed with cyclophosphamide. After 4 days, the mice were inoculated intranasally with 1.5 × 10E7 spores of Lichtheimia corymbifera or 1.0 × 10E7 spores of Aspergillus fumigatus. They were randomized and treated three times daily for 10 min with aerosolized 1% NCT or 0.9% sodium chloride starting 1 h after the inoculation. The mice were observed for survival for two weeks, and fungal load, blood inflammation parameters, bronchoalveolar lavage, and histology of organs were evaluated upon their death or at the end of this period. Inhalations were well-tolerated. After challenge with L. corymbifera, seven out of the nine mice (77.8%) survived for 15 days in the test group, which was in strong contrast to one out of the nine mice (11.1%) in the control group (p = 0.0049). The count of colony-forming units in the homogenized lung tissues came to 1.60 (1.30; 1.99; median, quartiles) log₁₀ in the test group and to 4.26 (2.17; 4.53) log₁₀ in the control group (p = 0.0032). Body weight and temperature, white blood count, and haptoglobin significantly improved with NCT treatment. With A. fumigatus, all the mice except for one in the test group died within 4 days without a significant difference from the control group. Inhaled NCT applied early demonstrated a highly significant curative effect in L. corymbifera pneumonia, while this could not be shown in A. fumigatus pneumonia, probably due to a too high inoculum. Nevertheless, this study for the first time disclosed efficacy of NCT in pneumonia in vivo.

Assessing Differences between Clinical Isolates of Aspergillus fumigatus from Cases of Proven Invasive Aspergillosis and Colonizing Isolates with Respect to Phenotype (Virulence in Tenebrio molitor Larvae) and Genotype

The fungus Aspergillus fumigatus, the cause of invasive aspergillosis (IA), is a serious risk to transplant patients and those with respiratory diseases. Host immune suppression is considered the most important factor for the development of IA. Less is known about the importance of fungal virulence in the development of IA including the significance of variation between isolates. In this study, isolates of A. fumigatus from cases diagnosed as having proven IA or colonisation (no evidence of IA) were compared in assays to measure isolate virulence. These assays included the measurement of radial growth and protease production on agar, sensitivity to UV light and oxidative stressors, and virulence in Tenebrio molitor (mealworm) larvae. These assays did not reveal obvious differences in virulence between the two groups of isolates; this provided the impetus to conduct genomic analysis. Whole genome sequencing and analysis did not allow grouping into coloniser or IA isolates. However, focused analysis of single nucleotide polymorphisms revealed variation in three putative genes: AFUA_5G09420 (ccg-8), AFUA_4G00330, and AFUA_4G00350. These are known to be responsive to azole exposure, and ccg-8 deletion leads to azole hypersensitivity in other fungi. A. fumigatus virulence is challenging, but the findings of this study indicate that further research into the response to oxidative stress and azole exposure are required to understand the development of IA.

Phylogenetic Distribution of csp1 Types in Aspergillus fumigatus and Their Correlates to Azole Antifungal Drug Resistance

In Aspergillus fumigatus, the repetitive region of the csp1 gene is one of the most frequently used loci for intraspecies typing of this human pathogenic mold. Using PCR amplification and Sanger sequencing of only a single marker, csp1 typing is readily available to most laboratories and highly reproducible. Here, I evaluate the usefulness of the csp1 marker for resistance detection and epidemiologic stratification among A. fumigatus isolates. After resolving nomenclature conflicts from published studies and adding novel csp1 types, the number of known types now adds up to 38. Their distribution mostly correlates with A. fumigatus population structure, and they are also meaningful for narrowly defined cases of azole resistance phenotypes. Isolates carrying the pandemic resistance allele TR34/L98H show signs of interclade crossing of strains with t02 or t04A, into the t11 clade. Furthermore, absolute differences in voriconazole MIC values between t02/t04B versus t11 TR34/L98H isolates indicate that the genetic background of resistance mutations may have a pivotal role in cross-resistance phenotypes and, thus, clinical outcome and environmental selection. Despite the general genetic similarity of isolates with identical csp1 types, outcrossing into other clades is also observed. The csp1 type alone, therefore, does not sufficiently discriminate genetic clades to be used as the sole marker in epidemiologic studies. IMPORTANCE Aspergillus fumigatus is a ubiquitously distributed saprophytic mold and a leading cause of invasive aspergillosis in human hosts. Pandemic azole-resistant strains have emerged on a global scale, which are thought to be propagated through use of azole-based fungicides in agriculture. To perform epidemiologic studies, genetic typing of large cohorts is key. Here, I evaluate the usefulness of the frequently used csp1 marker for resistance detection and epidemiologic stratification among A. fumigatus isolates. The phylogenetic distribution of csp1 types mostly correlates with A. fumigatus population structure and is also meaningful for narrowly defined cases of azole resistance phenotypes. Nevertheless, outcrossing of csp1 into other clades is also observed. The csp1 type alone, therefore, does not sufficiently discriminate genetic clades and should not be used as the sole marker in epidemiologic studies.

Aspergillus fumigatus and aspergillosis: From basics to clinics

The airborne fungus Aspergillus fumigatus poses a serious health threat to humans by causing numerous invasive infections and a notable mortality in humans, especially in immunocompromised patients. Mould-active azoles are the frontline therapeutics employed to treat aspergillosis. The global emergence of azole-resistant A. fumigatus isolates in clinic and environment, however, notoriously limits the therapeutic options of mould-active antifungals and potentially can be attributed to a mortality rate reaching up to 100 %. Although specific mutations in CYP 51A are the main cause of azole resistance, there is a new wave of azole-resistant isolates with wild-type CYP 51A genotype challenging the efficacy of the current diagnostic tools. Therefore, applications of whole-genome sequencing are increasingly gaining popularity to overcome such challenges. Prominent echinocandin tolerance, as well as liver and kidney toxicity posed by amphotericin B, necessitate a continuous quest for novel antifungal drugs to combat emerging azole-resistant A. fumigatus isolates. Animal models and the tools used for genetic engineering require further refinement to facilitate a better understanding about the resistance mechanisms, virulence, and immune reactions orchestrated against A. fumigatus. This review paper comprehensively discusses the current clinical challenges caused by A. fumigatus and provides insights on how to address them.

Clinical and experimental phenotype of azole-resistant Aspergillus fumigatus with a HapE splice site mutation: a case report

BACKGROUND

The recent increase in cases of azole-resistant Aspergillus fumigatus (ARAf) infections is a major clinical concern owing to its treatment limitations. Patient-derived ARAf occurs after prolonged azole treatment in patients with aspergillosis and involves various cyp51A point mutations or non-cyp51A mutations. The prognosis of patients with chronic pulmonary aspergillosis (CPA) with patient-derived ARAf infection remains unclear. In this study, we reported the case of a patient with ARAf due to HapE mutation, as well as the virulence of the isolate.

CASE PRESENTATION

A 37-year-old male was presented with productive cough and low-grade fever. The patient was diagnosed with CPA based on the chronic course, presence of a fungus ball in the upper left lobe on chest computed tomography (CT), positivity for Aspergillus-precipitating antibody and denial of other diseases. The patient underwent left upper lobe and left S6 segment resection surgery because of repeated haemoptysis during voriconazole (VRC) treatment. The patient was postoperatively treated with VRC for 6 months. Since then, the patient was followed up without antifungal treatment but relapsed 4 years later, and VRC treatment was reinitiated. Although an azole-resistant isolate was isolated after VRC treatment, the patient did not show any disease progression in either respiratory symptoms or radiological findings. The ARAf isolated from this patient showed slow growth, decreased biomass and biofilm formation in vitro, and decreased virulence in the Galleria mellonella infection model compared with its parental strain. These phenotypes could be caused by the HapE splice site mutation.

CONCLUSIONS

This is the first to report a case demonstrating the clinical manifestation of a CPA patient infected with ARAf with a HapE splice site mutation, which was consistent with the in vitro and in vivo attenuated virulence of the ARAf isolate. These results imply that not all the ARAf infections in immunocompetent patients require antifungal treatment. Further studies on the virulence of non-cyp51A mutations in ARAf are warranted.

In-host microevolution of Aspergillus fumigatus: A phenotypic and genotypic analysis

In order to survive, Aspergillus fumigatus must adapt to specific niche environments. Adaptation to the human host includes modifications facilitating persistent colonisation and the development of azole resistance. The aim of this study is to advance understanding of the genetic and physiological adaptation of A. fumigatus in patients during infection and treatment. Thirteen A. fumigatus strains were isolated from a single chronic granulomatous disease patient suffering from persistent and recurrent invasive aspergillosis over a period of 2 years. All strains had identical microsatellite genotypes and were considered isogenic. Whole genome comparisons identified 248 non-synonymous single nucleotide polymorphisms. These non-synonymous mutations have potential to play a role in in-host adaptation. The first 2 strains isolated were azole susceptible, whereas later isolates were itraconazole, voriconazole and/or posaconazole resistant. Growth assays in the presence and absence of various antifungal stressors highlighted minor changes in growth rate and stress resistance, with exception of one isolate showing a significant growth defect. Poor conidiation was observed in later isolates. In certain drug resistant isolates conidiation was restored in the presence of itraconazole. Differences in virulence were observed as demonstrated in a Galleria mellonella infection model. We conclude that the microevolution of A. fumigatus in this patient has driven the emergence of both Cyp51A-independent and Cyp51A-dependent, azole resistance mechanisms, and additional phenotypes that are likely to have promoted fungal persistence.