A scanning electronmicroscopy investigation of the structure of colonies of different morphologies produced by phenotypic switching of Candida albicans.

Variant colony formation by Candida albicans has been described and the phenomenon of phenotypic switching has been studied extensively. Whereas the microstructure of non-variant colonies has been investigated by scanning electronmicroscopy (SEM), the relationship between switched variant colonies and microstructure has not been described. The object of this study was to investigate and compared by SEM the microstructure of the normal colony type and five common variant colony types of C. albicans and to determine whether a pattern of dimorphic growth could account for the characteristic colony morphologies. A general relationship between colony type and structure was observed; smooth colonies consisted entirely of blastospores whereas regular, irregular-wrinkled and semi-rough colonies consisted of different proportion of true hyphae and blastospores. Regular extreme-jagged shaped colonies consisted of an almost pure culture of pseudohyphae, and colonies producing aerial hyphae were composed of pseudo- and true hyphae, as well as blastospores. These results show a clear relationship between colony morphology and development of particular cell types.