Resistance to Polyene Antibiotics and Correlated Sterol Changes in Two Isolates of Candida tropicalis from a Patient with an Amphotericin B-resistant Funguria

Abstract

Two isolates of Candida tropicalis resistant to amphotericin B were obtained from a patient with pyelonephritis due to Candida. Isolate RI showed a twofold increase in resistance to amphotericin and to nystatin when compared with two sensitive strains of C. tropicalis and one of Candida albicans. Isolate R2 was extremely resistant to amphotericin B, etruscomycin, and nystatin. The sterols of RI, R2, and the sensitive strains of Candida were compared qualitatively by ultraviolet spectrophotometry, thin-layer chromatography, gas-liquid chromatography, and the Liebermann-Burchard reaction. Both polyene-resistant isolates had altered sterols. Rl contained an unidentified Δ^5,7 sterol and little, if any, ergosterol; R2 was totally lacking in Δ^5,7 sterols. Chromatographic analyses showed that R2 had three sterols that were distinguishable from lanosterol. It is concluded that the resistance of isolates R 1 and R2 to polyene antibiotics is a consequence of their altered sterol composition.