Genetic diversity in clinical isolates of the dimorphic fungus Blastomyces dermatitidis detected by a PCR-based random amplified polymorphic DNA assay.

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Blastomyces dermatitidis is a dimorphic fungus causing localized or systemic infection in areas where the organism is endemic in the central and southeastern United States. In this study, 19 independent isolates of B. dermatitidis from Little Rock, Ark., were grouped into three classes based on restriction fragment length polymorphism patterns in mitochondrial DNA with a heterologous probe from Histoplasma capsulatum. One large class of 15 isolates and two smaller classes (classes 2 and 3), each consisting of two isolates, were observed in BglII digests. Strain-specific arrays of PCR-amplified DNA products were obtained with arbitrarily selected primers (18 to 29 nucleotides long; G+C contents, 33 to 56%). In the large class 1 group, 13 isolates could be differentiated by the random amplified polymorphic DNA (RAPD) method with various primers. The two remaining class 1 isolates were obtained from the same patients and produced identical RAPD arrays. Dissimilar RAPD patterns were obtained from the smaller class 2 group but not from the class 3 isolates. Significant genetic diversity in clinical isolates of B. dermatitidis was observed; this may underscore a similar environmental diversification. Further application of the typing techniques may provide significant insight into the epidemiology of blastomycosis and aid in the assessment of specific virulence phenotypes.

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