Veterinary Fusarioses within the United States

Abstract

Multilocus DNA sequence data were used to assess the genetic diversity and evolutionary relationships of 67 Fusarium strains from veterinary sources, most of which were from the United States. Molecular phylogenetic analyses revealed that the strains comprised 23 phylogenetically distinct species, all but two of which were previously known to infect humans, distributed among eight species complexes. The majority of the veterinary isolates (47/67 = 70.1%) were nested within the Fusarium solani species complex (FSSC), and these included 8 phylospecies and 33 unique 3-locus sequence types (STs). Three of the FSSC species (Fusarium falciforme, Fusarium keratoplasticum, and Fusarium sp. FSSC 12) accounted for four-fifths of the veterinary strains (38/47) and STs (27/33) within this clade. Most of the F. falciforme strains (12/15) were recovered from equine keratitis infections; however, strains of F. keratoplasticum and Fusarium sp. FSSC 12 were mostly (25/27) isolated from marine vertebrates and invertebrates. Our sampling suggests that the Fusarium incarnatum-equiseti species complex (FIESC), with eight mycoses-associated species, may represent the second most important clade of veterinary relevance within Fusarium Six of the multilocus STs within the FSSC (3+4-eee, 1-b, 12-a, 12-b, 12-f, and 12-h) and one each within the FIESC (1-a) and the Fusarium oxysporum species complex (ST-33) were widespread geographically, including three STs with transoceanic disjunctions. In conclusion, fusaria associated with veterinary mycoses are phylogenetically diverse and typically can only be identified to the species level using DNA sequence data from portions of one or more informative genes.

FIG 1

Maximum parsimony phylogram inferred from a 2-locus data set comprising portions of the DNA-directed RNA polymerase II largest (RPB1, 1,607 bp) and second largest (RPB2, 1,779 bp) subunits for 67 veterinary strains and nine fusaria from other sources. Gray highlight is used to identify the fusaria from other sources. Sequences of three medically important species within the F. dimerum species complex (32) were used to root the phylogram based on more inclusive analyses (22). Isolates of veterinary importance are nested within eight species complexes (identified using bold internodes) and comprise 23 phylogenetically distinct species. Each isolate is identified by a 5-digit ARS Culture Collection accession number (http://nrrl.ncaur.usda.gov/). Because Latin binomials cannot be applied with confidence, Arabic numbers and lowercase Roman letters, respectively, were used to identify species and 3-locus haplotypes within the F. solani, F. incarnatum-equiseti, and F. chlamydosporum species complexes as previously reported (16, 18). In addition, a 2-locus typing scheme (17) was used to identify five isolates within the F. oxysporum species complex as ST33. Numbers above internodes represent maximum parsimony bootstrap support based on 1,000 pseudoreplicates of the data. CI, consistency index; PIC, parsimony informative character; RI, retention index.