Calcium regulates in vitro dimorphism in chromoblastomycotic fungi.

Cladosporium carrionii, Fonsecaea pedrosoi and Phialophora verrucosa, the three most important agents of chromoblastomycosis, produced large numbers of sclerotic bodies at 25 degrees C, and greater numbers at 37 degrees C, after inoculation into a defined pH 2.5 medium containing 0.1 mmol l-1 Ca2+. Higher concentrations of Ca2+ reversed this tendency and promoted maintenance of hyphal growth. Addition of the Ca2+ chelator EGTA to the same medium buffered at pH 6.5 also induced sclerotic bodies, but in a more concentration-dependent fashion. EGTA at 0.5-1.0 mmol l-1 induced maximum numbers of sclerotic bodies in Cl. carrionii, whereas 2 and 8 mmol l-1 concentrations were required for the same results with F. pedrosoi and P. verrucosa, respectively. These findings suggest that Ca2+ concentrations in human tissue may play a paramount role in the dimorphic switching between hyphae and sclerotic bodies among chromoblastomycotic agents during infection.