Genetic diversity among clinical and environmental isolates of Aspergillus fumigatus

Abstract

To determine if cases of invasive aspergillosis (IA) were caused by strains of Aspergillus fumigatus with unique characteristics, strains from immunosuppressed patients with IA were compared to strains obtained from sputa of patients with cystic fibrosis and to strains from the environment. An extremely high genomic diversity was observed among the 879 strains typed by Southern blotting with a retrotransposon-like element from A. fumigatus (C. Neuvéglise, J. Sarfati, J. P. Latgé, and S. Paris, Nucleic Acids Res. 24:1428-1434, 1996). Analysis of Southern blot hybridization patterns showed the absence of clustering between environmental isolates and clinical isolates from patients with IA or cystic fibrosis. In addition, strains could not be clustered depending on their geographical location. This study implies that practically any strain of A. fumigatus is potentially pathogenic and can provoke a case of IA when it encounters a favorable environment in an immunosuppressed host.

Cryptic Speciation in the Cosmopolitan and Clonal Human Pathogenic Fungus Aspergillus Fumigatus

“…Our inability to discover any correlation between genotype and geography in a global collection of A. fumigatus individuals makes this fungus the first to be shown by population genetic evidence to have a global population structure with no endemism. Our result is consistent with earlier studies of more limited scope, for example, no correlation was found between genotype and geography for European and North American individuals (Debeaupuis et al 1997), nor for isolates from French and Italian patients (Bertout et al 2001), nor for environmental and clinical isolates from Canada (Rosehart et al 2002). Neither has any correlation between genotype and geography been found in another, study using a different collection of A. fumigatus individuals and different genetic markers (Rydholm et al 2003).…”

“…Our data support the hypothesis that any isolate of either the ''fumigatus'' or the ''occultum'' clade is a potential pathogen, an idea originally formulated from European and North American collections of A. fumigatus (Debeaupuis et al 1997, Bart-Delabesse et al 1998, see also Rosehart et al 2002). These taxa are accidental human pathogens and are not transmitted from host to host; infection provides no apparent benefit to the fungi.…”

“…Even in the genus Aspergillus, species with restricted geographic ranges have been found; For example, one of the phylogenetic species of A. flavus predominated in equatorial regions and the southern hemisphere (Tran-Dinh 2003). In contrast to these studies, prior research on A. fumigatus found no correlation between membership in any of several clades and geography (Debeaupuis et al 1997). However, sampling by Debeaupuis et al (1997) was restricted to individuals from the Northern Hemisphere (Europe and the United States), and we aimed to test their conclusions by assembling our own collection of individuals from Africa, Latin America, and Asia, as well as Europe and North America.…”

“…PSR has been used in another morphological species of Aspergillus, A. flavus, to describe cryptic species (Geiser et al 1998a) and previous research on Northern hemisphere isolates of A. fumigatus used genetic fingerprint data to show that individuals could be divided into several distinct clades, suggestive of cryptic speciation (Debeaupuis et al 1997). However, because fingerprint data can be problematic due to unavoidable assumptions regarding the homology of fragments of a similar size, in this study of A. fumigatus we used DNA sequence variation of five polymorphic loci to develop multilocus sequence genotypes.…”

Environmental surveillance and other control measures in the prevention of nosocomial fungal infections

“…It is important to remember that genetic analysis cannot discriminate between clinical and environmental isolates of A. fumigatur, indicating that every strain present in the environment is a potential pathogen if it encounters the appropriate host [32]. Thus, the degree of exposure assessed by CFUs per unit of ambient air is not predictive of disease; the actual risk appears to vary with the underlying condition.…”