Ultrastructure of Candida parapsilosis endocarditis.

We used light microscopy and scanning and transmission electron microscopy to study the structure of Candida parapsilosis vegetations on five surgically removed porcine bioprosthetic valves. Scanning electron microscopy revealed a "mossy" amorphous surface. In some areas, C. parapsilosis cells could be seen below the surface layer. In areas in which the vegetation had cracked, myriads of healthy C. parapsilosis cells were seen to be loosely adherent to one another. These cells were covered with a flocculent or fibrillar matrix. A compact intercellular matrix was evident by transmission electron microscopy. Hyphal elements were seen invading valvular tissue. The loose matrix that bound large clumps of C. parapsilosis cells explains why large emboli are frequent complications of Candida endocarditis.