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Specific chromosome alterations in fluconazole-resistant mutants of Candida albicans
V Perepnikhatka1, F J Fischer, M Niimi
1Department of Biochemistry and Biophysics, University of Rochester Medical School, Rochester, New York 14642, USA.
Abstract:
The exposure of Candida albicans to fluconazole resulted in the nondisjunction of two specific chromosomes in 17 drug-resistant mutants, each obtained by an independent mutational event. The chromosomal changes occurred at high frequencies and were related to the duration of the drug exposure. The loss of one homologue of chromosome 4 occurred after incubation on a fluconazole medium for 7 days. A second change, the gain of one copy of chromosome 3, was observed after exposure for 35 or 40 days. We found that the mRNA levels of ERG11, CDR1, CDR2, and MDR1, the candidate fluconazole resistance genes, remained either the same or were diminished. The lack of overexpression of putative drug pumps or the drug target indicated that some other mechanism(s) may be operating. The fluconazole resistance phenotype, electrophoretic karyotypes, and transcript levels of mutants were stable after growth for 112 generations in the absence of fluconazole. This is the first report to demonstrate that resistance to fluconazole can be dependent on chromosomal nondisjunction. Furthermore, we suggest that a low-level resistance to fluconazole arising during the early stages of clinical treatment may occur by this mechanism. These results support our earlier hypothesis that changes in C. albicans chromosome number is a common means to control a resource of potentially beneficial genes that are related to important cellular functions.
Insights
Candida albicans developed fluconazole resistance through chromosome nondisjunction, not gene overexpression. This mechanism, involving chromosome number changes, offers a new understanding of antifungal drug resistance.
Area of Science:
- Microbiology
- Genetics
- Molecular Biology
Background:
- Antifungal drug resistance is a growing clinical concern.
- Mechanisms of azole resistance in Candida albicans are not fully understood.
- Previous hypotheses suggested chromosome number alterations in C. albicans.
Purpose of the Study:
- To investigate the role of chromosomal nondisjunction in fluconazole resistance in Candida albicans.
- To determine if gene expression changes correlate with fluconazole resistance.
- To assess the stability of resistance mechanisms.
Main Methods:
- Inducing drug resistance in Candida albicans through sequential exposure to fluconazole.
- Analyzing chromosomal changes using electrophoretic karyotyping.
- Quantifying the expression levels of key resistance genes (ERG11, CDR1, CDR2, MDR1) via mRNA analysis.
Main Results:
- Seventeen independent mutants exhibited nondisjunction of chromosomes 4 and 3 after fluconazole exposure.
- Chromosomal changes occurred with high frequency, correlating with drug exposure duration.
- No significant overexpression of candidate resistance genes was observed; mRNA levels remained unchanged or decreased.
- Resistance phenotype and karyotype were stable over 112 generations without drug pressure.
Conclusions:
- Fluconazole resistance in Candida albicans can be mediated by chromosomal nondisjunction, a novel mechanism.
- This chromosomal instability may contribute to low-level resistance during early clinical treatment.
- Chromosome number alterations represent a significant adaptive strategy for C. albicans.