Distinct Phenotype and Secondary Metabolite Profile Mark a Dominant Aspergillus flavus Outbreak Strain

An Aspergillus flavus outbreak strain dominated the indoor environment in a Danish hospital ward for eight years and subsequently multiple isogenic infections occurred. We investigated whether strain-specific traits were present to understand its prevalence and persistence. The outbreak strain was studied alongside comparator A. flavus isolates with respect to altered virulence that could enhance its pathogenic potential and secondary metabolism that could influence environmental persistence. Twenty-four isolates were examined for growth patterns on ten media and by secondary metabolite profiling using high-performance liquid chromatography with diode-array detection. Strain-specific virulence and other phenotypic traits were studied in vivo using Galleria mellonella and in vitro by culturing on specialised media. No indication of virulence alterations was observed in larvae. However, the outbreak strain exhibited a reproducible fingerprint phenotype with distinct morphological features and secondary metabolites. These included mycotoxins known to be harmful to humans and animals. Although this study found no evidence of increased virulence, identification of a distinct phenotypic profile could indicate adaptation or an intrinsic ecological background of the outbreak strain and possibly competitive traits via potentially bioactive secondary metabolites. Moreover, the production of several mycotoxins by this A. flavus strain raises concerns for both patients and staff. Further analyses of the strain's ecology, toxic potential, virulence, and phylogeny in a global context could be studied in future experiments.