Does intraspecies variation in Aspergillus fumigatus affect infection outcomes? : a phenotype/genotype study using an insect model

Abstract

Aspergillus fumigatus is a saprophytic soil-fungus and an opportunistic human pathogen. This haploid mould reproduces asexually using spores that can readily become airborne. In immunocompromised individuals, inhalation of A. fumigatus spores can lead to a pulmonary infection termed 'invasive aspergillosis' (IA). Despite extensive research on human immunity and treatment, the relative contribution of fungal genetic and phenotypic variation to the outcomes of infection is yet to be elucidated. In the present study, I sought to determine the pathogenic relevance of the intraspecies variation of A. fumigatus. Clinical isolates were characterised using phenotypic assays (UV resistance, amphotericin-B resistance, radial growth rate) and whole genome sequenced to determine genetic relatedness. These data were integrated with virulence data generated in an insect infection model, Tenebrio molitor larvae, to determine the relevance of fungal variation to clinical outcomes, identify potential virulence factors, and further our understanding of A. fumigatus pathogenesis in invasive aspergillosis. I observed a high level of intraspecies heterogeneity in all pathogenesis-associated phenotypic properties. The spectrum of core-genome single nucleotide polymorphisms (SNPs) present and virulence in T. molitor larvae also varied between isolates. Patterns of intraspecies variation aligned with clinical origin for two properties: growth rate on nutrient rich media and virulence in T. molitor. The correlation between clinical origin and both growth rate and virulence suggests a contribution of fungal biology towards clinical outcomes. The low level of virulence displayed by IA isolates relative to colonisers suggests the biology of IA isolates may be optimised for overcoming clinical challenges not modelled in T. molitor larvae. Finally, the absence of strong clustering of isolates based on their clinical origin suggests more focused or non-SNP based assays of variation may be necessary to reveal any genomic markers of a strains ability to cause invasive disease.

Date of Award	2019
Original language	English