Molecular Genetic Insights into the Dimorphic Fungal Pathogen Blastomyces dermatitidis

The epidemiology of blastomycosis remains poorly understood in part due to the lack of a robust and discriminatory strain typing method for Blastomyces dermatitidis. Here we describe the development of a multilocus sequence (MLST) method to study the genetic variation and population structure of B. dermatitidis. Eighty geographically diverse clinical and environmental isolates were examined. Thirty-six unique sequence types were identified. With a discriminatory index of 91.4%, MLST identifies significant genetic diversity for the characterization of local and global B. dermatitidis isolates. To test whether this fungus represented a single species throughout its geographic range we performed phylogenetic analyses, applying Genealogical Concordance Phylogenetic Species Recognition (GCPSR). Phylogenetic analysis revealed two distinct clades, with five of the eight gene phylogenies studied supporting the separation of these lineages, which were also geographically partitioned. Based on fulfillment of GCPSR, we propose the current species B. dermatitidis harbors two genetically distinct non-interbreeding phylogenetic species.MAS