Background: Aspergillus fumigatus (AF) is the predominant cause of invasive aspergillosis (IA). IA occurs in severely immunocompromised patients and has a high mortality rate due to inadequate diagnostic tools and suboptimal treatment regimens. A better understanding of the pathobiology of this fungus is essential for the development of new diagnostic tools and therapies. In previous studies we identified an array of genes that were differentially transcribed in AF during interaction with human neutrophils. We chose three genes for functional studies: adm-A, nr and mbl, encoding proteins from the ADAM metalloprotease, the nitroreductase and the metallo-beta-lactamase families, respectively. These genes exhibited higher transcriptional levels in conidia and/or hyphae treated with neutrophils from normal donors compared to those treated with neutrophils from CGD patients that were defective in the production of reactive oxygen species. Methods: The genes were deleted from AF strain B-5233 via Agrobacterium-mediated transformation. Fungal cell viability was determined by XTT assay. Neutrophils were isolated from normal donors. Results: Deletion of adm-A, nr and mbl had no impact on growth rate but significantly affected conidial and hyphal resistance to H2O2 and menadione. Compared to the wild type, conidia of all 3 deletants exhibited higher tolerance to H2O2 but lower tolerance to menadione. In hyphae, the wild type and the deletants showed the same tolerance to both agents, with exception to the nr deletant, which was more susceptible to menadione. Preliminary assays showed that the wild type and the deletants nr and adm-A exhibited the same susceptibility to neutrophils whereas the mbl deletant appeared more sensitive. Conclusion: The differential behavior of the deletant strains underscores the complexity of the pathobiology of AF. Though these three genes do not appear to be metabolically linked, our findings suggest that they are all involved in resistance to oxidative stress. Further studies, such as virulence in the mouse model, are underway to clarify the role of each of these genes in the response of AF to host defenses.
Full conference title:
110th General Meeting American Society for Microbiology
- ASM 110th (2010)