The C.albicans DDR48 stress response protein is essential for filamentation, virulence, and confers partial antifungal drug resistance. (c2007)

Abstract

Candida albicans is a pathogenic yeast that causes mucosal and systemic infections. C. albicans pathogenicity is attributed to its ability to exist in different morphological states and to respond to stress by up regulating several genes. Many genes involved in stress response have been partially characterized. DDR48 is a stress associated gene involved in DNA repair and in response to antifungal drug exposure. The aim of the present study is to investigate any possible role of DDR48 in vitro filamentation and in vivo virulence in a mouse systemic infection model by generating a homozygous null mutant strain. Furthermore, this study attempts to assess the antifungal drug susceptibilities of the mutant strain against azoles, amphotericin B, and caspofungin drugs in vitro. It was observed that DDR48 was haploid insufficient and essential, SInce only a heterozygote, but not a homozygous null mutant was generated. On corn meal agar, the heterozygote strain caused a delay of chlamydospore and hyphae formation with respect to the parental BWP17 strain. However, the heterozygote DDR48/ddr48 strain, unlike the parental strain, was non filamentous on potato dextrose agar plus 50% fetal bovine serum, and on 50% fetal bovine serum medium. Furthermore, the heterozygote mutant showed additional defects in filamentation formation on Lee's medium, and on M199 pH7.5 as BWP17 formed an extensive network of filaments whereby the heterozygous strain exhibited defective filamentation formation. When cultured in fetal bovine serum, the heterozygote strain formed short aberrant germ tubes within 12 hours whereas the parental strain formed an extensive hyphal network within 6 hours. In vivo, the mice survival rate was 66 % after 33 days of post infection with the heterozygous strain, as opposed to rapid death within 10 days with the parental strain. DDR48/ddr48 was also susceptible dose dependent to itraconazoles and fluoconazoles compared with the wildtype parental strain and susceptible to ketoconazoles. However, both the heterozygote and parental strain were sensitive to caspofungin, voriconazoles, and resistant to amphotericin B. In sum, the diminished virulence phenotype of the heterozygous mutant reflects the essential role of the DDR48 in filamentation and pathogenesis.