Submitted to: Journal of Clinical Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/5/2009
Publication Date: 12/1/2010
Citation: O Donnell, K., Sutton, D.A., Rinaldi, M.G., Gueidan, C., Crous, P.W., Geiser, D.M. 2010. A Novel Multi-Locus Sequence Typing Scheme Reveals High Genetic Diversity of Human Pathogenic Members of the Fusarium incarnatum-F. equiseti and F. chlamydosporum Species Complexes within the U. S. Journal of Clinical Microbiology. 47(12):3851-3861. Interpretive Summary: Fusarium species have emerged over the past three decades as one of the most important groups of human opportunistic pathogens. Collectively, members of the F. incarnatum-equiseti [FIESC] and F. chlamydosporum [FCSC] species complexes account for approximately 15% of all fusarial infections of humans and other animals within the U. S. In addition, these fungi produce a variety of toxins that pose a significant threat to human health and food safety. In the present study, multilocus DNA typing schemes were developed for members of the FIESC and FCSC for the first time. Results of the present study revealed that the FIESC and FCSC respectively comprise 28 and four genetically distinct species which can only be identified accurately using the DNA typing methodology. Being able to accurately identify these toxigenic human pathogens will greatly facilitate communication of their population biology and epidemiology within the public health community. Results of the present study will be of interest to and benefit clinical microbiologists, mycotoxicologists and plant pathologists.
Technical Abstract: Results of the present study reveal that members of the Fusarium incarnatum-equiseti (FIESC) and F. chlamydosporum species complexes (FCSC) collectively account for approximately 15% of all fusarial infections of humans and other animals within the U. S. Moreover, the diverse toxins these fungi produce pose a significant concern to human health and food safety. Herein species limits within these evolutionary lineages were investigated for the first time using genealogical concordance of multilocus DNA sequence data to resolve phylogenetically distinct species (GCPSR). Maximum parsimony and maximum likelihood analyses of aligned DNA sequences from four loci resolved 28 species within the FIESC, within which the species were evenly divided among two clades designated Incarnatum and Equiseti, and four species within the FCSC. Sequence data from a fifth locus, beta tubulin, was excluded from the study due to the presence of highly divergent, homoplaseous paralogs. Because most of the species lack Latin binomials, and because fusarioses appear to be increasing in clinical relevance, the multilocus haplotype nomenclature adopted in a previous study (K. O’Donnell, D. A. Sutton, A. Fothergill, D. McCarthy, M. G. Rinaldi, M. E. Brandt, N. Zhang, and D. M. Geiser, J. Clin. Microbiol. 46:2477-2490, 2008) was expanded to all of the species within the FIESC and FCSC to provide the first DNA sequence-based typing schemes for these fusaria, thereby facilitating future epidemiological investigations. Multilocus DNA typing identified sixty-two sequence types (STs) among 88 FIESC isolates and 20 STs among 26 FCSC isolates. FIESC 15-a and 15-c, and FCSC 2-a were the most common STs. The former two STs were restricted to Texas and Oklahoma, whereas FCSC 2-a was geographically more widespread with isolates from the Texas, Pennsylvania and Australia. Lastly, four human and two veterinary isolates, received as members of the FIESC or FCSC, were resolved as five phylogenetically distinct species nested outside these species complexes. To our knowledge, these five species heretofore have not been reported to cause mycotic infections (i.e., F. armeniacum, F. brachygibbosum, F. flocciferum, and two unnamed Fusarium species within the F. tricinctum species complex).