Virulence of South African Candida albicans strains isolated from different clinical samples.

Candida albicans is a dimorphic opportunistic pathogenic yeast that is commonly isolated from different anatomical sites and clinical samples. It possesses several virulence factors, including secretion of hydrolytic enzymes, the ability to adhere to abiotic surfaces and cells, and the ability to penetrate tissues. We determined the level of in vitro expression of virulence factors by South African clinical C. albicans strains and the correlation among them. Furthermore, we determined whether there is a correlation between the levels of virulence factors expressed by a strain and the anatomical site from which it was isolated. The overall virulence of strains expressing different levels of these virulence factors in vitro was examined using a chorioallantoic membrane (CAM) chicken embryo model of infection, with variations observed in the production of hydrolytic enzymes. Most strains were able to produce in vitro high levels of protease and phospholipase and medium levels of lipase. Using the quantitative agar invasion assay, most strains were found to be highly invasive. No relationships of virulence factors produced in vitro were observed, except for a weak negative correlation between protease activity and invasiveness, as well as protease activity and cell surface hydrophobicity. There was no indication that the in vitro differences in virulence factors were correlated with virulence in the CAM model. However, we found that the infection model is sensitive enough to distinguish different virulence levels of strains.