Submitted to: Journal of Clinical Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2006
Publication Date: 6/3/2006
Citation: Zhang, N., O Donnell, K., Sutton, D.A., Nalim, A., Samuels, G.J., Summerbell, R.C., Padhye, A.A., Geiser, D.M. 2006. Members of the Fusarium solani species complex causing infections in both humans and plants are those most commonly encountered in the environment. Journal of Clinical Microbiology. 44(6):2186-2198. Interpretive Summary: The several hundred species within the filamentous mold genus Fusarium collectively comprise the most important group of fungal pathogens of plants worldwide. Moreover, the diverse arrays of toxins they produce pose a serious threat to food safety and animal health. Due in large part to the dramatic rise in artificially immunosuppressed and immunocompromised patients over the past twenty-five years, fusaria have emerged as one of the most important groups of opportunistic, filamentous fungal pathogens of humans. The present molecular genetic study was conducted to determine which species within the Fusarium solani species complex [FSSC] are responsible for infections of humans and other animals. To this end, we genetically typed 471 strains, including 278 from patients, by analyzing DNA sequence data from parts of four genes. The major finding of this study is that FSSC infections of humans and other animals are caused by at least 18 genetically distinct species. This research has produced the first comprehensive DNA database of the FSSC pathogens, thereby facilitating the development of molecular tools for the surveillance of these life-threatening opportunistic pathogens, especially within hospital environments.
Technical Abstract: Members of the Fusarium solani species complex (FSSC) are increasingly implicated as the causative agents of human mycoses, particularly in the expanding immunocompromised and immunosuppressed patient populations. Best known as ubiquitous plant pathogens and saprotrophs, members of FSSC comprise over 45 phylogenetically distinct species distributed among three major clades. To identify which species are associated with human infections, we generated multilocus haplotypes based on four partial gene sequences from 471 isolates. Of these, 278 were from human patients, 21 from hospital environments, and 183 from non-clinical sources. Phylogenetic trees inferred from an ergosterol biosynthesis gene (erg-3) were highly discordant with those inferred from the three other partial gene sequences; therefore, this partition was analyzed separately. Multilocus analysis showed that isolates from humans were restricted to but spread throughout clade 3 of the FSSC phylogeny, comprising at least 18 phylogenetically distinct species. The majority (73.8%) of the clinical isolates, however, were associated with four major lineages designated Groups 1-4. Groups 1 and 2 were strongly supported as phylogenetic species, whereas Groups 3 and 4 were not. Although isolates from ocular infections were found in all four groups, they had a significant tendency to belong to Group 3 (P<0.001). Human clinical isolates shared identical multilocus haplotypes with isolates from plants, other animals, and from hospital environments, suggesting potential nosocomiality. The major finding of this study is that FSSC-associated mycoses of humans and other animals have origins in a broad phylogenetic spectrum, indicating widespread ability to cause infection in this diverse species complex.