Colony variations in Candida species

One hundred isolates of seven Candida species and three isolates of Saccharomyces cerevisiae were plated on phloxine B agar and examined for variations in the morphology or colour of colonies that developed. Colony variations were found in 9 of 12 C. parapsilosis isolates, 8 of 13 C. tropicalis isolates, 4 of 9 C. krusei isolates and 12 of 30 C. albicans isolates. None of 23 C. glabrata isolates grew on the test medium. Variant colonies often generated further different colony forms on secondary subculture. The rate of production of fimbriate and rhizoid colonies by two C. albicans isolates varied with agar thickness and the nutrient content of the medium. These results suggest that colony variation is a common property among isolates of many Candida species and that strict control of agar medium thickness and composition is essential for reproducible screening of isolates for colony variations.