Evaluation of the in vitro and in vivo dimorphism ofSporothrix schenckii,Blastomyces dermatitidis, andParacoccidioides brasiliensisisolates after preservation in mineral oil

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Abstract
Morphological differentiation has commanded attention for its putative impact on the pathogenesis of invasive fungal infections. We evaluated in vitro and in vivo the dimorphism from mycelial to yeast-phase of Sporothrix schenckii, Blastomyces dermatitidis and Paracoccidioides brasiliensis isolates, two strains for each species, preserved in mineral oil. S. schenckii strains showed typical micromorphology at 25 °C but one strain was unable to complete the dimorphic process in vitro. After in vivo passage through mice the strains had the ability to turn into yeast-like cells and to form colonies on brain-heart infusion medium at 36 °C. B. dermatitidis strains grew as dirty white to brownish membranous colonies at 25 °C and their micromorphology showed thin filaments with single hyaline conidia. At 36 °C the colonies did not differ from those grown at 25 °C, but produced a transitional micromorphology. P. brasiliensis strains grew as cream-colored cerebriform colonies at 25 °C showing a transitional morphology. B. dermatitidis and P. brasiliensis strains did not turn into yeast-like cells in vivo. The present results demonstrate that B. dermatitidis and P. brasiliensis strains were unable to complete the dimorphic process even after in vivo passage, in contrast to the S. schenckii strain.Key words: pathogenic fungi, in vitro storage, in vivo passage, morphogenesis.