Candida albicans Mutations in the Ergosterol Biosynthetic Pathway and Resistance to Several Antifungal Agents

Abstract

The role of sterol mutations in the resistance of Candida albicans to antifungal agents has not been thoroughly investigated. Previous work reported that clinical C. albicans strains resistant to both azole antifungals and amphotericin B were defective in ERG3, a gene encoding sterol ⌬ 5,6 -desaturase. It is also believed that a deletion of the lanosterol 14␣-demethylase gene, ERG11, is possible only under aerobic conditions when ERG3 is not functional. We tested these hypotheses by creating mutants by targeted deletion of the ERG3 and ERG11 genes and subjecting those mutants to antifungal susceptibility testing and sterol analysis. The homozygous erg3/erg3 mutant created, DSY1751, was resistant to azole derivatives, as expected. This mutant was, however, slightly more susceptible to amphotericin B than the parent wild type. It was possible to generate erg11/erg11 mutants in the DSY1751 background but also, surprisingly, in the background of a wild-type isolate with functional ERG3 alleles under aerobic conditions. This mutant (DSY1769) was obtained by exposure of an ERG11/erg11 heterozygous strain in a medium containing 10 g of amphotericin B per ml. Amphotericin B-resistant strains were obtained only from ERG11/erg11 heterozygotes at a frequency of approximately 5 ؋ 10 ؊5 to 7 ؋ 10 ؊5 , which was consistent with mitotic recombination between the first disrupted erg11 allele and the other remaining functional ERG11 allele. DSY1769 was also resistant to azole derivatives. The main sterol fraction in DSY1769 contained lanosterol and eburicol. These studies showed that erg11/erg11 mutants of a C. albicans strain harboring a defective erg11 allele can be obtained in vitro in the presence of amphotericin B. Amphotericin B-resistant strains could therefore be selected by similar mechanisms during antifungal therapy.

The Candida albicans homologue of PIG-P, CaGpi19p: gene dosage and role in growth and filamentation

“…This polyene antibiotic is used clinically for treatment of candidiasis and reports of resistant strains are rare. Ergosterol levels are reported to be the main cause for resistance to this drug, with both increased as well as decreased levels of ergosterol being correlated with amphotericin B sensitivity (Pasrija et al, 2005;Sanglard et al, 2003). In many reports of fungal resistance to this drug, there have also been increases in chitin or glucan levels (Bahmed et al, 2002;Seo et al, 1999).…”

Multiple functions of ergosterol in the fission yeast Schizosaccharomyces pombe

“…cerevisiae and Candida species, many experiments have demonstrated a role for ergosterol in physiological functions, such as membrane permeability, resistance to drugs, protein transport to the plasma membrane, sporulation and endocytosis (Geber et al, 1995;Parks et al, 1999;Young et al, 2003;Sanglard et al, 2003;Pasrija et al, 2005a, b;Mukhopadhyay et al, 2002;Proszynski et al, 2005;Enyenihi & Saunders, 2003;Munn et al, 1999;Heese-Peck et al, 2002;Kishimoto et al, 2005). In addition, an association between many plasma membrane proteins and DRMs has been studied and some DRMassociated proteins have been identified (Dupré & Haguenauer-Tsapis, 2003;Bagnat et al, 2000Bagnat et al, , 2001Umebayashi & Nakano, 2003;Malinska et al, 2004;Grossmann et al, 2006;Lauwers & André, 2006).…”

Influences of cinnamic aldehydes on H+ extrusion activity and ultrastructure of Candida

“…Of the two prominent classes of antifungals, polyenes cause serious host toxicity (Kauffman & Carver, 1997;Cohen, 1998), whereas azoles are fungistatic and their prolonged use contributes to the development of drug resistance in Candida albicans and other species (Dupont et al, 1996;Sanglard et al, 2003). This has prompted the search for novel, less toxic molecules that can be developed as antifungals.…”