Measuring intraspecific variation in the response of clinical isolates of Aspergillus fumigatus to oxidative stress.

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.