Extracellular proteolysis by Mucoraceae in serum-albumin agar tested by the agar block method.

In a preliminary study, three strains of Absidia corymbifera (two strains from autopsy material of the lungs and one from the soil of a potted indoor plant in a hospital) and one strain of Rhizopus oryzae (from the soil of a potted plant in a hospital) were tested for secretory proteolytic activity in serum-albumin agar (SAA) with initial pH values of 5.0 and 7.0 by the agar block method and subsequent protein staining. Within an incubation period of 5 d/37 degrees C, complete proteolysis took place in all the SAA blocks with an initial pH value of 7.0. The three strains of Absidia corymbifera and the one strain of Rhizopus oryzae did not fully proteolyse the SAA blocks with an initial pH value of 5.0. On the basis of these observations, it is assumed that there are secretory proteases in the causative agents of mucormycosis (zygomycosis) whose optimal pH is not in the acid but in the neutral, perhaps in the alkaline range.