Scanning Electron Microscopy of Colonies of Six Species of Candida

Abstract

Thirty strains of six species of Candida isolated from patients were cultured for 60 h on Sabouraud agar, freeze-dried, and examined with a scanning electron microscope. The colonies were circular ( Candida albicans, C. guilliermondii ) or oval ( C. tropicalis, C. pseudotropicalis, C. krusei, C. parakrusei ) in outline, and those of C. pseudotropicalis and C. krusei had an irregular outline due to a peripheral pseudomycelium. The morphology of individual microorganisms was examined at the margins and apex of those species which lacked a surface coat ( C. pseudotropicalis, C. krusei, C. parakrusei, C. guilliermondii ), and through cracks in the surface coating of those which showed a surface coat ( C. albicans, C. tropicalis ). All species showed buds, bud scars, and interconnecting intercellular processes, but were generally spherical ( C. albicans, C. tropicalis ) or ovoid ( C. pseudotropicalis, C. krusei, C. parakrusei, C. guilliermondii ) in fixed preparations. In unfixed material, individual organisms were almost invariably indented. Fixation with 3% glutaraldehyde and washing before freeze-drying caused partial removal of the surface coating of colonies of C. albicans and C. tropicalis , which persisted only as irregular sheets or as a filamentous meshwork. This filamentous meshwork was also present among the organisms of colonies of C. albicans, C. tropicalis , and C. pseudotropicalis . It is concluded that these filaments represent the precipitation or unmasking of some component of the intercellular matrix of these organisms.