Detection of extracellular phospholipase activity in Candida albicans and Rhodotorula rubra

Phospholipases are important pathogenicity determinants in Candida albicans. They play a significant role in damaging cell membranes and invading host cells. High phospholipase production is correlated with an increased ability of adherence and a higher mortality rate in animal models. By means of an egg yolk-containing agar and the Pz (= phospholipase activity zone) value according to Price, the present study investigated phospholipase production in 170 strains of C. albicans. At an incubation temperature of 37 degrees C, Pz values ranged from 0.395 to 1; no clear relationship was found between clinical origin of the isolates and severity of the disease. In addition to C. albicans, a total of 110 strains of 16 other yeast species were investigated for possible phospholipase production. Only yeasts of the species Rhodotorula rubra showed phospholipase activity, with mean values exceeding those observed in C. albicans. This result was confirmed by an assay using sterile culture filtrates and phosphatidyl-[3H-methyl]-choline-dipalmitoyl as a substrate. Since Rh. rubra has only rarely been demonstrated as a pathogen in humans, we believe that factors such as reduced growth at 37 degrees C, absence of dimorphism and low ability of adherence lessen the importance of high phospholipase activity in Rh. rubra as a pathogenicity determinant. Therefore, potential virulence factors should always be considered in the context of the whole spectrum of pathogenic determinants.