Affiliation:
1. Division of Medicinal Chemistry and Pharmacology, Janssen Research Foundation, Beerse, Belgium.
Abstract
A Candida (Torulopsis) glabrata strain (B57149) became resistant to fluconazole after a patient carrying the organism was treated with the drug at 400 mg once daily for 9 days. Growth of the pretreatment isolate (B57148) was inhibited by 50% with 0.67 microM ketoconazole, 1.0 microM itraconazole, and 43 microM fluconazole, whereas growth of B57149 was inhibited slightly by 10 microM ketoconazole but was unaffected by 10 microM itraconazole or 100 microM fluconazole. This indicates cross-resistance to all three azole antifungal agents. The cellular fluconazole content of B57149 was from 1.5- to 3-fold lower than that of B57148, suggesting a difference in drug uptake between the strains. However, this difference was smaller than the measured difference in susceptibility and, therefore, cannot fully explain the fluconazole resistance of B57149. Moreover, the intracellular contents of ketoconazole and itraconazole differed by less than twofold between the strains, so that uptake differences did not account for the azole cross-resistance of B57149. The microsomal cytochrome P-450 content of B57149 was about twice that of B57148, a difference quantitatively similar to the increased subcellular ergosterol synthesis from mevalonate or lanosterol. These results indicate that the level of P-450-dependent 14 alpha-demethylation of lanosterol is higher in B57149. Increased ergosterol synthesis was also seen in intact B57149 cells, and this coincided with a decreased susceptibility of B57149 toward all three azoles and amphotericin B. B57149 also had higher squalene epoxidase activity, and thus, more terbinafine was needed to inhibit the synthesis of 2,3-oxidosqualene from squalene. P-450 content and ergosterol synthesis both decreased when isolate B57149 was subcultured repeatedly on drug-free medium. This repeated subculture also fully restored the strain's itraconazole susceptibility, but only partly increased its susceptibility to fluconazole. The results suggest that both lower fluconazole uptake and increased P-450-dependent ergosterol synthesis are involved in the mechanism of fluconazole resistance but that only the increased ergosterol synthesis contributes to itraconazole cross-resistance.
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Pharmacology (medical),Pharmacology
Reference42 articles.
1. Isolation of Candida tropicalis gene for P450 lanosterol demethylase and its expression in Saccharomyces cerevisiae;Chen C.;Biochem. Biophys. Res. Commun.,1987
2. The fungicide resistance problem;Dekker J.;Neth. J. Plant Pathol.,1977
3. Characterization of fenarimol-resistant mutants of Aspergillus nidulans;De Waard M. A.;Neth. J. Plant Pathol.,1977
4. Dupont B. 1992. Antifungal therapy in AIDS patients p. 290-300. In J. E. Bennett R. J. Hay and P. K. Peterson (ed.) New strategies in fungal disease. Churchill Livingstone Edinburgh.
5. Resistance au fluconazole en milieu hospitalier. Concordance entre la resistance de Candida albicans in vitro et l'6chec therapeutique;Dupouy-Camet J.;Presse Med.,1991
Cited by
193 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献