Rapid Induction of High-frequency MTL Homozygosis and Microbiological Polymorphism in Candida albicans by Fluconazole

Candida α lbicans is most common fungal pathogen of opportunistic infections. C.
albicans was previously, noted as a diploid, apparently asexual fungus. Morphological and
genetic studies had found mating type-like locus (MTL a/α) and demonstrated its relations to
morphological switching, virulence, and f1uconazole-resistance. A parasexual cycle was found
between opposite MTL homozygotes. However, C. albicans was found with MTL
homozygous genotype in only around 3.2 % of clinical s仕ains ， and MTL heterozygotes had a
low 企equency (about 10勻of white-opaque (刺刀0) switch to be MTL homozygotes in nature.
In the present study, reference C. αlbicans strain SC5314 was used for f1uconazole-inducing
assay to harvest 35 first-generation survival daughter strains from 70 colonies picked 企om
f1uconazole inhibitory zone. Further separation with spreading culture and micromanipulator
methods was further employed to gain second- and third-generation strains with accordance to
first-generation daughter strains. PCR analysis based on MTL a1 ， α1 and cf2 was employed to
demonstrate MTL genotypes of these isolates. Microscopic observation and f1owcytometry
assay were employed for cell/colony morphology and DNA content analysis on progeny
SC5314 and its daughter strains. High 企equency of MTL gene loss (24 of 35, 68.57 %) and
homozygotes (16 of 鈣， 45.71 % ) were found in f1uconazole-inducing survival daughter
strains with accordance to first-generation daughter strains. Polymorphism of ceIVcolony
morphology and decreasing DNA content were also found in these f1uconazole-inducing
daughter strains. Fluconazole treatment not only inhibited the growth of C. α lbicans but also
altered phenotypic characteristics in ceIVcolony morphology as well as induced rapid highfrequency
MTL gene loss and homozygosity in f1uconazole inhibition zone. The DNA content
of these f1uconazole-inducing daughter strains were also obviously reduced with comparison
to their progeny SC5314 suggesting a possibility of chromosome loss and DNA
rearrangement during the f1uconazole treatment to C. albicαns.