Polyene-Resistant Mutants of Aspergillus fennelliae : Identification of Sterols

Abstract

Four mutants strains of Aspergillus fennelliae resistant to various polyene antibiotics have been analyzed for their sterol content. The mutant strains contained A7'22 24(2 8-ergostatrien-3#-ol and A7 22-ergostadien-3,3-ol as the major sterols, whereas the wild types contained ergosterol, indicating that the mutants contain metabolic blocks for C,-C, dehydrogenation and C24-C28 reduction in the biosynthesis of ergosterol. Revertant sectors arising from the mutant colonies contained either more A7.22-ergostadien-3#-ol than the parent mutant strain or showed the reappearance of ergosterol. The revertant sectors also showed lower resistance to amphotericin B and a higher rate of sporulation than the parent mutant strain. These results confirm our previous observations that the presence of ergosterol is directly related to the drug susceptibility and the normal rate of sporulation in this species.The development of resistance to polyene antibiotics in fungi has been shown to coincide with alterations in the sterol content of the cells (1,2,(5)(6)(7)(10)(11)(12)(13)(14).In 1972 (2) identified several biosynthetic precursors of ergosterol as the major sterols in nystatin-resistant mutants of S. cerevisiae. A mutant of S. cerevisiae resistant to relatively low concentrations of nystatin was found to contain as a major sterol 5,6-dihydroergosterol, an immediate precursor of ergosterol. The mutants resistant to higher concentrations of nystatin, on the other hand, containing earlier precursors such as A7. 22, 24(28 '-ergostatrien-3fl-ol, A8, 22, 24(28)-ergostatrein -3f-ol, and fecosterol (Al8 24 (28 )-ergostadien-3#-ol.We have recently reported observations of polyene resistance and correlated sterol changes in the mutants of Aspergillus fennelliae (10). In this communication, we report the identification of the sterols accumulated in the mutants of A. fennelliae. Evidence supporting our previous hypothesis that ergosterol is one of the necessary components for the normal rate of asexual and sexual sporulation is also presented. MATERIALS AND METHODSStrains and cultural conditions. The polyeneresistant mutants, AF4-NS1, p-NS1, AF5-AB1, p-AB1, and wild-type strains of A. fennelliae, described elsewhere (10), were used in this experiment. The wild-type strains were maintained on a malt extractagar medium, and the mutants were maintained on the same medium but containing 4 tsg of amphotericin B per ml for AF5-AB1 and p-AB1 and 10 U of nystatin per ml for AF4-NS1 and p-NS1. For sterol extractions, the strains were cultured in malt extract-broth medium at 30 C on a gyrotory shaker (115 rpm) for 5 days. To isolate a reverse mutant, AF5-AB1 and p-AB1 were maintained also on drug-free malt extract-agar medium.Sterol extraction and purification. Mycelial pads grown on malt extract medium were washed once in distilled water and saponified with 30% methanolic KOH at reflux for 3 h before the sterols were extracted with hexane (10). The hexane extracts were then washed with distilled water, and the solvent was evaporated under a str...

Amphotericin B resistance of Aspergillus terreus in a murine model of disseminated aspergillosis

“…A similar ergosterol content has been described in a strain of A. fumigatus which is susceptible to amphotericin B in vivo [23,24]. Polyene antifungal resistance has previously been attributed to lesions in the ergosterol biosynthetic pathway in clinical isolates of Candida albicans [22,25,26] and Cryptococcus neoformans [27] and in laboratory mutants of C. albicans [22,28], A. fennelliae [29] and of a protozoan, Leishmania donovani [30]. Nevertheless, amphotericin B resistance has also been reported in C. albicans [31], Cr.…”

Polyene Macrolide Antibiotic Biosynthesis

“…These are ineffective against Pneumocystis carinii, which has cholesterol instead of ergosterol [38]. The emergence of polyene resistant fungi due to the presence of sterols other than ergosterol in their membranes has also been reported [39][40][41][42].…”

The Production of Reactive Oxygen Species Is a Universal Action Mechanism of Amphotericin B against Pathogenic Yeasts and Contributes to the Fungicidal Effect of This Drug

“…Different approaches have demonstrated that mutants resistant to AMB have reduced ergosterol content (74)(75)(76)(77)(78)(79)(80)(81)(82). In contrast, resistance to AMB has also been reported in isolates without any ergosterol defect (83)(84)(85).…”