Phenotypic chracterization of blastomyces dermatitidis

Blastomyces dermatitidis is a dimorphic fungal pathogen associated with severe repiratory and disseminated disease in humans. Recent investigations suggest that the two major genetic groups of the fungus are associated with different clinical outcomes. This study extends that work by exploring how laboratory phenotypic traits (mating locus type, ability to mate, spore production and antifungal susceptibility) might vary by genetic group. Among 100 clinical and environmental isolates, both genetic groups had roughly equal distributions of the ?-box and HMG loci. Additionally, crosses between compatible strains of group 1 and group 2 organisms yielded visible cleistothecia and ascospores, suggesting that mating between the two groups could be possible in natural settings. Experiments related to spore production were found to be very difficult to standardize and the results were not interpretable. Although only a small group of isolates were tested for antimicrobial susceptibility testing, results showed that several strains had high MICs to amphotericin B. These results have significant clinical implications and should be confirmed on a larger group of isolates. Also, the new techniques developed as part of this study will provide a foundation for incorporating susceptibility testing of dimorphic fungal pathogens into the clinical laboratory