Proliferation of intracellular structure corresponding to reduced affinity of fluconazole for cytochrome P-450 in two low-susceptibility strains of Candida albicans isolated from a Japanese AIDS patient.
Three Candida albicans isolates, TIMM 3164, 3165 and 3166 with reduced fluconazole susceptibility, were isolated from two Japanese AIDS patients. We earlier reported that a reduced intracellular accumulation of fluconazole in these isolates played an important role in the resistance mechanism of fluconazole, but we did not exclude the involvement of other factors. We here examined characteristics related to cytochrome P-450 (CYP), especially sterol 14alpha-demethylase encoded by the ERG11 gene which is the target molecule for fluconazole. In TIMM 3164 and 3165, the ergosterol synthesis by cell-free extracts was somewhat less susceptible to fluconazole, due to a decrease in fluconazole affinity for CYP. The nucleotide substitutions in the ERG11 gene were identified to result in three amino acid changes of K143R, E266D and V488I in TIMM 3164, and of E266D, V404L and V488I in TIMM 3165. These amino acid substitutions might contribute to the decreased affinity for CYP in both isolates. However, a single amino acid change, E266D, observed in TIMM 3166 was unrelated to the decreased affinity for CYP. The most prominent finding on the ultrastructure of TIMM 3164 and 3165 was the development of mesh membrane structures of the endoplasmic reticula, which is a location related to sterol synthesis. This phenomenon was not observed in the cells of TIMM 3166 or the susceptible control strains of ATCC 90028 and 10231. In addition to the reduced intracellular accumulation, the decreased affinity of fluconazole for CYP in TIMM 3164 and 3165 is assumed to be associated with the fluconazole-resistance phenotype.
Maebashi
Kazunori
K
Teikyo University Institute of Medical Mycology, Hachioji, Tokyo 192-0395, Japan. kazunori_maebashi@meiji.co.jp
Kudoh
Michinari
M
Nishiyama
Yayoi
Y
Makimura
Koichi
K
Kamai
Yasuki
Y
Uchida
Katsuhisa
K
Yamaguchi
Hideyo
H
D017088:AIDS-Related Opportunistic Infections / Q000382:microbiology; D019943:Amino Acid Substitution; D000935:Antifungal Agents / Q000494:pharmacology*; D002176:Candida albicans / Q000187:drug effects* / Q000254:growth & development / Q000302:isolation & purification / Q000648:ultrastructure*; D002180:Candidiasis, Oral / Q000382:microbiology; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D025141:Drug Resistance, Fungal / Q000235:genetics*; D004875:Ergosterol / Q000378:metabolism; D015725:Fluconazole / Q000494:pharmacology*; D006801:Humans; D007564:Japan; D008826:Microbial Sensitivity Tests; D008854:Microscopy, Electron; D009097:Multienzyme Complexes / Q000235:genetics / Q000378:metabolism; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism
D000935:Antifungal Agents; D009097:Multienzyme Complexes; C023939:4-methyl sterol demethylase; D015725:Fluconazole; D003577:Cytochrome P-450 Enzyme System; D010088:Oxidoreductases; D004875:Ergosterol