No abstract

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 the 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 very challenging, but the findings of this study indicate that further research into response to oxidative stress and azole exposure are required to understand the development of IA.

Objective In this study, the survival of clinical isolates of the pathogenic fungus Aspergillus fumigatus against the oxidative stressors, hydrogen peroxide and menadione, and UV light, was examined to see if there was variation between isolates and if the variation was linked to virulence. Results Fifteen isolates were tested, five from cases of invasive aspergillosis (IA isolates) and ten from cases where the fungus had colonised a patient (colonising isolates). Exposure to UV light and hydrogen peroxide did not show significant differences between the groups of isolates. Colonising isolates showed a trend for greater survival when treated with hydrogen peroxide, mean survival 18.9%, compared to IA isolates, mean survival 8%. Treatment with 50mM menadione confirmed this trend in colonising isolates with an average conidial survival of 72% compared to 50% in IA isolates. Overall significant sensitivity to 50mM menadione was observed in 1/10 colonising isolates compared to 4/5 IA isolates. Increased sensitivity to oxidative stress in IA isolates may seem counterintuitive but could be utilised as an indicator of pathogenic potential in isolates of the fungus and be used in further studies to unravel the complex interplay between host and pathogen.