In Vitro Low-Level Resistance to Azoles in Candida albicans Is Associated with Changes in Membrane Lipid Fluidity and Asymmetry

Abstract

The present study tracks the development of low-level azole resistance in in vitro fluconazole-adapted strains of Candida albicans, which were obtained by serially passaging a fluconazole-susceptible dose-dependent strain, YO1-16 (fluconazole MIC, 16 g ml ؊1 ) in increasing concentrations of fluconazole, resulting in strains YO1-32 (fluconazole MIC, 32 g ml ؊1 ) and YO1-64 (MIC, 64 g ml ؊1 ). We show that acquired resistance to fluconazole in this series of isolates is not a random process but is a gradually evolved complex phenomenon that involves multiple changes, which included the overexpression of ABC transporter genes, e.g., CDR1 and CDR2, and the azole target enzyme, ERG11. The sequential rise in fluconazole MICs in these isolates was also accompanied by cross-resistance to other azoles and terbinafine. Interestingly, fluorescent polarization measurements performed by using the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene revealed that there was a gradual increase in membrane fluidity of adapted strains. The increase in fluidity was reflected by observed change in membrane order, which was considerably decreased (decrease in fluorescence polarization values, P value) in the adapted strain (P value of 0.1 in YO1-64, compared to 0.19 in the YO1-16 strain). The phospholipid composition of the adapted strain was not significantly altered; however, ergosterol content was reduced in YO1-64 from that in the YO1-16 strain. The asymmetrical distribution of phosphatidylethanolamine (PE) between two monolayers of plasma membrane was also changed, with PE becoming more exposed to the outer monolayer in the YO1-64 strain. The results of the present study suggest for the first time that changes in the status of membrane lipid phase and asymmetry could contribute to azole resistance in C. albicans.

The Effect of Plagiochin E Alone and in Combination with Fluconazole on the Ergosterol Biosynthesis of Candida albicans

“…CDR1-mediated drug resistance was susceptible to changes in membrane fluidity. 17,18) Our initial investigations showed that PLE can obviously reduce the expression of CDR1, 9) which may be influenced by imbalances in membrane lipid composition.…”

Mechanism of Fluconazole Resistance in Candida albicans Biofilms: Phase-Specific Role of Efflux Pumps and Membrane Sterols

“…These investigators suggested that the altered membrane sterol pattern provided a common basis for antifungal resistance by preventing the binding of a drug and/or reducing its permeability (22). Recent reports also suggest that changes in the status of the membrane lipid phase and asymmetry could contribute to azole resistance in C. albicans (27,36). Moreover, microarray analyses revealed that the ERG2 (encoding the ergosterol biosynthesis pathway enzyme C-8 sterol isomerase) and CDR1 genes are upregulated in a planktonically grown fluconazole-resistant strain of C. albicans (46).…”

Propiconazole Toxicity on the Non-Target Organism, the Arbuscular Mycorrhizal Fungus, Glomus irregulare

“…This ratio saturated/unsaturated FA increase suggested a modification in membrane composition and is in agreement with the study of Benyagoub et al (1996) which reported an increase in membrane fluidity on Fusarium oxysporum when exposed to an antifungal compound. In the same way, Kohli et al (2002) found an increase of membrane fluidity in Candida albicans treated with azoles. The disturbance in the unsaturated FA, especially the polyunsaturated C18:3, in the presence of propiconazole reminds an induction of lipid peroxidation.…”