Phenotypic variation of a virulent Candida albicans strain and two spontaneous, relatively avirulent mutant strain derivatives.

The effect of media and temperature of incubation on colony phenotype of Candida albicans strain 4918, and two relatively avirulent mutant strains, designated 4918-2 and 4918-10, has been investigated. In addition, the strains were characterized on the basis of morphotyping pattern. Colony phenotypes were determined for cultures grown on either Lee's medium supplemented with arginine and zinc, or M63 medium supplemented with casamino acids. Incubation was at either 24 or 37 degrees C for 7 days. The results demonstrated that the predominant colony phenotype observed at 24 degrees C was different from that at 37 degrees C for all three strains, irrespective of the medium. While the growth medium influenced the specific colony phenotypes observed, as well as their categorical distribution, no significant medium effect on switching frequency was apparent. The switching repertoire of strain 4918-10 was consistently more varied than either the parental strain or 4918-2 under the conditions examined. However, categorization of the colony phenotypes shown by the three strains suggested that the pattern exhibited by strain 4918-2 was distinct from that of the other two strains. In addition, individual primary colonies of each phenotype observed were clonally plated in order to examine further the switching frequencies. The results established that all three strains were capable of high frequency switching. Other experiments demonstrated that morphotypes of all three strains were different from one another as expected from the differences in their virulence reported previously.