Search

Aspergillus fumigatus is an environmental filamentous fungus that can cause life-threatening disease in immunocompromised individuals. The interactions between A. fumigatus and the host environment are dynamic and complex. The host immune system needs to recognize the distinct morphological forms of A. fumigatus to control fungal growth and prevent tissue invasion, whereas the fungus requires nutrients and needs to adapt to the hostile environment by escaping immune recognition and counteracting host responses. Understanding these highly dynamic interactions is necessary to fully understand the pathogenesis of aspergillosis and to facilitate the design of new therapeutics to overcome the morbidity and mortality caused by A. fumigatus. In this Review, we describe how A. fumigatus adapts to environmental change, the mechanisms of host defence, and our current knowledge of the interplay between the host immune response and the fungus.

Echinocandins inhibit β-1,3-glucan synthesis and are one of the few antimycotic drug classes effective against Aspergillus spp. In this study, we characterized the β-1,3-glucan synthase Fks1 of Aspergillus fumigatus, the putative target of echinocandins. Data obtained with a conditional mutant suggest that fks1 is not essential. In agreement, we successfully constructed a viable Δfks1 deletion mutant. Lack of Fks1 results in characteristic growth phenotypes similar to wild type treated with echinocandins and an increased susceptibility to calcofluor white and sodium dodecyl sulfate. In agreement with Fks1 being the only β-1,3-glucan synthase in A. fumigatus, the cell wall is devoid of β-1,3-glucan. This is accompanied by a compensatory increase of chitin and galactosaminogalactan and a significant decrease in cell wall galactomannan due to a massively enhanced galactomannan shedding. Our data furthermore suggest that inhibition of hyphal septation can overcome the limitations of echinocandin therapy. Compounds inhibiting septum formation boosted the antifungal activity of caspofungin. Thus, development of clinically applicable inhibitors of septum formation is a promising strategy to improve existing antifungal therapy., (© 2014 John Wiley & Sons Ltd.)

alpha-Glucosidase I regulates trimming of the terminal alpha-1,2-glucose residue in the N-glycan-processing pathway, which plays an important role in the quality control system in mammalian cells. However, the consequence of glucose trimming of the N-glycan in filamentous fungi is unclear. We identified the gene encoding alpha-glucosidase I in the human opportunistic fungal pathogen Aspergillus fumigatus, namely Afcwh41. Deletion of the Afcwh41 gene resulted in a defective N-glycan processing of the proteins secreted by A. fumigatus. Although the Afcwh41 was not essential for hyphal growth and virulence, a severe reduction in conidia formation and a temperature-sensitive deficiency of cell wall integrity (CWI) were observed. Also, abnormalities of polar growth and septation were observed during conidial germination and hyphal elongation of the mutant. Our results suggest that Afcwh41 was involved in CWI, polarity, septation, and conidiation in A. fumigatus, probably by affecting the proper function of the proteins that are required for cell wall synthesis.

Autophagy is a highly conserved eukaryotic mechanism whereby cells recycle cellular elements to survive under adverse conditions. Surprisingly, of the three fungal pathogens of greatest relevance to human health, only Cryptococcus neoformans has been shown to require this process during infection. In contrast, autophagy is dispensable for the virulence of both Candida albicans and Aspergillus fumigatus. The divergent roles for autophagy in these opportunistic species underscore the uniqueness of the host infection niche occupied by each fungus and provide insights into the evolutionary pressures that may have influenced the need for autophagy during infection. Further study of fungal autophagy may reveal the host signals which induce this protective response and determine if these signals differ between host cells or tissues. In addition, a comprehensive understanding of the autophagy machinery in fungal pathogens may provide a rational basis for the design of future therapeutic interventions to improve outcome in patients who are at risk for these infections.

This is a case of vocal cord aspergillosis in a 36-year-old woman whose chief complaint was progressive hoarseness and vocal fatigue of one month duration. These symptoms followed the use of systemic administration of penicillin, cefotaxime natrium and dexamethasone to treat her rhinitis and asthma. Fiberoptic laryngoscopy revealed whitish plaques involving both vocal cords. Microscopic examination of KOH preparations and histopathology studies of tissue revealed dichotomously branching, hyaline, septate hyphae. Morphological and molecular biological identification of the fungal growth in cultures inoculated with clinical specimens from the patient indicated that the etiologic agent was Aspergillus fumigatus. The patient was cured with oral itraconazole without any side effects.

The calcineurin pathway is a critical signal transduction pathway in fungi that mediates growth, morphology, stress responses, and pathogenicity. The importance of the calcineurin pathway in fungal physiology creates an opportunity for the development of new antifungal therapies that target this critical signaling pathway. In this study, we examined the role of the zinc finger transcription factor Crz1 homolog (CrzA) in the physiology and pathogenicity of the opportunistic human fungal pathogen Aspergillus fumigatus. Genetic replacement of the crzA locus in A. fumigatus resulted in a strain with significant defects in conidial germination, polarized hyphal growth, cell wall structure, and asexual development that are similar to but with differences from defects seen in the A. fumigatus DeltacnaA (calcineurin A) strain. Like the DeltacnaA strain, the DeltacrzA strain was incapable of causing disease in an experimental persistently neutropenic inhalational murine model of invasive pulmonary aspergillosis. Our results suggest that CrzA is an important downstream effector of calcineurin that controls morphology in A. fumigatus, but additional downstream effectors that mediate calcineurin signal transduction are likely present in this opportunistic fungal pathogen. In addition, the importance of CrzA to the production of disease is critical, and thus CrzA is an attractive fungus-specific antifungal target for the treatment of invasive aspergillosis.

In a previous work we demonstrated a clear link between elastase activity and pathogenicity using what we have named the Elastase Activity Index (EAI). In the present study we have evaluated the possible variability of this index as a consequence of successive inoculations in mice. Two strains of Aspergillus fumigatus isolated from the environment without elastase activity were used. These strains were inoculated into successive batches of ten mice. Our results showed that with each inoculation there was an increase in the number of mice on each batch from which the strain could be isolated and an increase in the number of strains with an EAI>1. This study suggests that A. fumigatus could adapt to the environment in which it is developed, increasing its pathogenic capabilities from host to host.

Introduction: Aspergillosis colonisation in cystic fibrosis (CF), usually due to Aspergillus fumigatus (AF), classically presents as allergic bronchopulmonary aspergillosis. However, aspergillus infection can produce a range of manifestations: from minor colonization to an invasive infection., Case Report: A 14-year-old CF patient, chronically colonized with Staphylococcus aureus and Pseudomonas aeruginosa, presented with acute right-sided chest pain, a moderate fever and no modification of the sputum. The chest X-ray showed a 5 cm round opacity. Laboratory parameters were WBC 24,500 G/l, CRP 27 mg/l, Total IgE 1527 UI/l, Specific Aspergillus fumigatus IgE 31 UI/l. Bronchoscopy revealed external compression of the middle lobe bronchus with mucopurulent secretions coming from apical segment of the lower lobe. Bronchoalveolar lavage revealed the presence of pseudomonas aeruginosa 103 CFA/ml, staph aureus 107 CFA/ml and one colony of AF. Chest CT scan showed a large necrotic mass with an air-fluid level located in the apical segment of the right lower lobe. Initial therapy with itraconazole and corticosteroid was replaced by voriconazole, caspofungin, metronidazole and linezolide. Treatment was well tolerated and after 8 weeks the chest X-ray appearances had returned to normal., Conclusions: The possible diagnoses and therapeutic options are discussed. Conventional antifungal treatment with amphotericin B is limited by nephrotoxicity. These newer antifungal agents appear to be effective and well-tolerated.

Dissemination of aspergillosis into the central nervous system is associated with nearly 100% mortality. To study the reasons for the antifungal immune failure we analyzed the efficacy of cerebral complement to combat the fungus Aspergillus. Incubation of Aspergillus in non-inflammatory cerebrospinal fluid (CSF) revealed that complement levels were sufficient to obtain a deposition on the surface, but opsonization was much weaker than in serum. Consequently complement deposition from normal CSF on fungal surface stimulated a very low phagocytic activity of microglia, granulocytes, monocytes and macrophages compared to stimulation by conidia opsonized in serum. Similarly, opsonization of Aspergillus by CSF was not sufficient to induce an oxidative burst in infiltrating granulocytes, whereas conidia opsonized in serum induced a clear respiratory signal. Thus, granulocytes were capable of considerably reducing the viability of serum-opsonized Aspergillus conidia, but not of conidia opsonized in CSF. The limited efficacy of antifungal attack by cerebral complement can be partly compensated by enhanced synthesis, leading to elevated complement concentrations in CSF derived from a patient with cerebral aspergillosis. This inflammatory CSF was able to induce (i) a higher complement deposition on the Aspergillus surface than non-inflammatory CSF, (ii) an accumulation of complement activation products and (iii) an increase in phagocytic and killing activity of infiltrating granulocytes. However, levels and efficacy of the serum-derived complement were not reached. These data indicate that low local complement synthesis and activation may represent a central reason for the insufficient antifungal defense in the brain and the high mortality rate of cerebral aspergillosis.

Omphalitis associated with aspergillosis was diagnosed in four cases of commercial turkey poults ranging in age from 3 to 9 days old. In two cases, the mycotic agent present in the yolk sac was isolated and identified as Aspergillus fumigatus. In the other two cases, the fungi were identified as Aspergillus sp. on the basis of morphologic characteristics of the fungi in tissue sections. The fungi present were further confirmed to be of the genus Aspergillus by immunohistochemistry. Omphalitis by A. fumigatus infection has not been documented before.

A rapid method based on solid phase cytometry (SPC) for the detection of Aspergillus fumigatus hyphae is described. With an enzymatic "viability" staining procedure, fungal hyphae can be detected non-specifically within the hour. By combining this procedure with an immunofluorescence labelling, a distinction between Aspergillus spp. and other clinically important fungi is possible, except for Penicillium spp. due to cross-reactivity. To differentiate both genera, microcolonies are generated by incubation at 45 degrees C prior to viability staining. The latter approach in conjunction with immunofluorescence labelling allows a quasi-specific detection of A. fumigatus hyphae and has shown its applicability to samples of bronchoalveolar lavage liquid (BAL).

The Aspergillus fumigatus group splits into the anamorphic A. fumigatus series and the teleomorphic Neosartorya fischeri series. The species A. fumigatus Fresenius is the most common species within the A. fumigatus series. Forty-seven clinical isolates out of the A. fumigatus group were obtained from patients with diseases such as localized and invasive aspergilloses or allergic disorders due to Aspergillus and were mainly isolated from respiratory secretions. Isolates were studied concerning macro- and micromorphological parameters. All isolates were shown to be isolates of the species A. fumigatus Fresenius. In general, the macro- and micromorphological variability between the different isolates was low. Four isolates (DSM 10661, DSM 10662, DSM 10705, DSM 11069) showed significant differences towards the type strain A. fumigatus Fresenius ATCC 1022; one of these isolates was highly atypical (DSM 10705).

Pseudallescheria boydii is an opportunistic fungus that is histologically indistinguishable from Aspergillus fumigatus. Pseudallescheria boydii has been reported to cause endophthalmitis, orbital cellulitis, and corneal ulceration and is, thus, important to the ophthalmologist. A clinical review of 17 patients with P boydii ophthalmic infections is presented. In addition, animal models of endophthalmitides caused by A fumigatus and P boydii were created and compared. Dutch-Belted rabbits used for the experimental models were immunosuppressed with methylprednisolone acetate (Depomedrol). Exogenous and endogenous models of P boydii endophthalmitis were created in immunocompetent and immunosuppressed animals. An exogenous model of A fumigatus endophthalmitis was created in immunocompetent and immunosuppressed animals for comparison. The clinical and histopathologic features of A fumigatus and P boydii endophthalmitis are indistinguishable in the immunocompetent and immunosuppressed exogenously infected rabbits. Endogenous P boydii endophthalmitis has a similar fundus appearance to that caused by Nocardia asteroides.

This study concerns the use of the indirect immunoperoxidase technique for labelling Aspergillus species in infected human and animal tissues in smears taken from cultures. Specific labelling without serious cross-reactivity with Candida species or Zygomycete fungi was demonstrated using antiserum to Aspergillus. However, it was not possible to distinguish between two Aspergillus species. A fumigatus and A. flavus with this technique. Pretreatment of sections with sodium azide and normal swine serum was effective in eliminating background staining. The method can be used to produce permanently stained sections and has applications in the recognition of hyphal fragments in tissue from infected patients.

Evidence suggests that neutrophils are important in host defenses against invasive aspergillosis and mucormycosis, although hyphae in these lesions are too large to be phagocytized. Interactions of neutrophils with hyphae of Aspergillus fumigatus and Rhizopus oryzae were studed in vitro. Light and electron microscopic observations indicated that neutrophils attached to and spread over the surfaces of hyphae, even in the absence of serum. This was followed by dramatic morphologic changes which suggested severe damage and probably death of hyphae. An assay of neutrophil-induced reduction of uptake of radioisotopes was used to quantitate damage to the fungi by neutrophils from normal subjects. Damage to hyphae was inhibited by a variety of compounds which are known to affect neutrophil surface functions, motility, and metabolism. Use of inhibitors of oxidative microbicidal mechanisms of neutrophils indicated the central importance of these mechanisms in damage to hyphae. Inhibitors of neutrophil cationic proteins altered damage only to Rhizopus. Damage to hyphae by lysozyme suggested that it may play a secondary role in the neutrophil, primarily against Aspergillus. This new nonphagocytic mechanism may play an important role in host defenses against these and other hyphal forms of fungi.

On the basis of cultural, morphological and developmental studies of the two Aspergillus isolates from the lungs of an aspergillosis patient, the taxonomic status of Aspergillus phialiseptus is discussed. The elimination of the name A. phialiseptus is proposed as the isolates were found by the authors to belong to A. fumigatus.