Examining the role of opportunistic human pathogen Aspergillus flavus in fungal keratitis eye infections

点击翻译按钮获取中文摘要

Project Summary Aspergillus species are a leading cause of fungal infections in humans as the disease agents for both aspergillosis respiratory infections and fungal keratitis (FK) eye infections. FK can necessitate a corneal transplant or have the devastating consequence of blindness. Over a million new cases of FK are reported annually worldwide. The primary risk factors for FK are contact lens use and surface scratches on the eye, which allow infection of the cornea; damage occurs as the fungus grows into the cornea. The filamentous fungus Aspergillus flavus is a leading cause of FK infections and is isolated from FK corneal ulcers more frequently than any other Aspergillus species, including closely related ones, such as A. parasiticus, A. nomius, and A. arachidicola. A. flavus is known to grow at the temperature of the human body (37°C), to produce bioactive secondary metabolites known as mycotoxins, and to tolerate high salinity levels, all of which are thought to be relevant for infection and growth in the human eye. However, we do not understand what genetic determinants of virulence are unique to A. flavus or how variation in these determinants contributes to within- and between-species variation in the ability of A. flavus to cause FK. The goal of my project is to understand what makes A. flavus a successful pathogen when other closely related, widespread Aspergillus species are not pathogenic as well as gain insights into variation in pathogenicity within A. flavus. I hypothesize that the A. flavus genome includes unique genetic determinants of virulence absent from related species. These may be genes or variants that are uniquely present or absent in A. flavus versus closely related non-pathogens, such as genes involved in secondary metabolism (secondary metabolites often affect host biology). We also do not yet know the genetic diversity, antifungal drug tolerance levels, or phenotypic responses to heat or salinity of FK-causing A. flavus isolates. I hypothesize that genetic and phenotypic traits differentially present in A. flavus and nonpathogenic relatives will also impact virulence. To test these hypotheses, I propose to first examine genomic diversity among Aspergillus species and within A. flavus to identify putative genetic determinants of virulence, and to examine the impact of unique determinants on virulence in an invertebrate model of disease. Second, I will investigate the impact of salinity, heat, and antifungal drugs on growth phenotypes and chemical profiles of A. flavus and related species, and to study the impact of secondary metabolites that are uniquely present in A. flavus on its virulence in an invertebrate model of disease. The proposed experiments will enable me to identify key differences in genetic elements between A. flavus and related species and provide a snapshot of population structure of clinical and environmental isolates within A. flavus, as well as characterize the physiological responses of A. flavus and related non-pathogenic species to infection-relevant conditions.