Mitochondrial resistance to miconazole in Saccharomyces cerevisiae

Ketoconazole and miconazole alter potassium homeostasis in Saccharomyces cerevisiae

The effects of ketoconazole and miconazole uptake on K(+) transport and the internal pH of Saccharomyces cerevisiae were studied. The uptake of both drugs was very fast, linear with concentration and not dependent on glucose, indicating entrance by diffusion and concentrating inside. Low (5.0μM) to intermediate concentrations (40μM) of both drugs produced a glucose-dependent K(+) efflux; higher ones also produced a small influx of protons, probably through a K(+)/H(+) exchanger, resulting in a decrease of the internal pH of the cells and the efflux of material absorbing at 260nm and phosphate. The cell membrane was not permeabilized. The K(+) efflux with miconazole was dependent directly on the medium pH. This efflux results in an increased membrane potential, responsible for an increased Ca(2+) uptake and other effects. These effects were not observed with two triazolic antifungals. A decrease of the Zeta (ζ) potential was observed at low concentrations of miconazole. Although the main effect of these antifungals is the inhibition of ergosterol synthesis, K(+) efflux is an important additional effect to be considered in their therapeutic use. Under certain conditions, the use of single mutants of several transporters involved in the movements of K(+) allowed to identify the participation of several antiporters in the efflux of the cation.

Drug-induced phenotypes provide a tool for the functional analysis of yeast genes

The post-genome sequencing era of Saccharomyces cerevisiae is defined by the analysis of newly discovered open reading frames of unknown function. In this report, we describe a genetic method for the rapid identification and characterisation of genes involved in a given phenotype. This approach is based on the ability of overexpressed genomic DNA fragments to cure an induced phenotype in yeast. To validate this concept, yeast cells carrying a yeast DNA library present on multicopy plasmid vectors were screened for resistance to the antifungal drug ketoconazole. Among 1.2 million colonies 13 clones tested positive, including those expressing the lanosterol C-14 demethylase, known to be a cellular target for azole drugs, and the cytochrome-c oxidase of mitochondria, regulating the respiratory chain electron transport. Several other resistant clones were identified, which code for yeast proteins of so far unknown function. These genes may represent potential candidates for antifungal drug effects. Together with the availability of the entire yeast genome sequence, the described genetic screening method is a powerful tool for the effective functional analysis of yeast genes.

A comparison of miconazole, ketoconazole and fluconazole in their effects on temperature-dependent growth and thermal death in Candida albicans

A strain of Candida albicans isolated from human sputum exhibited an associative temperature profile, with the initial maximum temperature = 42 degrees C, the final maximum temperature = 38 degrees C, and the minimum temperature of thermal death = 33 degrees C, showed a decrease in its cardinal temperatures and a reduction in the specific rates of growth and thermal death throughout the novel temperature ranges in the presence of either 25 microM of miconazole, ketoconazole or fluconazole. In the concentration range 0-30 microM, each drug concertedly depressed the kinetic and energetic parameters of growth, with lesser variation on the specific glucose transfer rate. The overall effect of miconazole was the greatest (up to one order of magnitude), while that of fluconazole was the least.

Drug resistance in human pathogenic fungi

Since the therapy of the mycoses, particularly the systemic mycoses, is relatively long-term in nature, emergence of resistance to antifungal drugs during the treatment of period would be of considerable clinical importance. However, most reports of resistance to antifungal agents among human pathogenic fungi indicate that naturally-occurring resistance is very rare, and that the induction of resistant mutants or variants is much more difficult to achieve in vitro and in vivo than with bacteria. As a matter of fact, amphotericin B and some other classic antifungals have not as yet posed a broadly significant problem relative to drug resistance despite their widespread and frequent use. Fungal resistance has thus received little attention, in contrast to the critical importance of bacterial resistance frequently caused by a variety of antibacterial chemotherapeutic agents, until a single exception to this generalization arose with the advent of flucytosine. This new development has aroused great interest in the problem of fungal resistance among the scientists involved with medical mycology. It is generally believed that fungi, like bacteria, are intrinsically capable of developing resistance to antifungal agents. As illustrated by flucytosine, inherently resistant mutants to antifungals occur within sensitive strains of human pathogenic fungi with significant frequency. Given the relatively high degree of such primary resistance, these mutants should develop secondary resistance during therapy, thus resulting in considerable limitations in the clinical usefulness of the antifungals. Virtually, all unsuccessful cases of mycoses treated with some of the recently exploited antifungal drugs, albeit scarce to date, would obviously be attributable to the occurrence of secondary resistance. The exploitation of new antifungal drugs thus requires investigations of their resistance as one of the most important research projects to be undertaken before receiving approval for use on humans. This paper reviews from various aspects the literature on resistance to various classic and novel antifungal agents among human pathogenic fungi. The resistance of some nonpathogenic fungi to these agents will also be described from genetic and biochemical points of view.

Isolation and analysis of ketoconazole resistant mutants of Saccharomyces cerevisiae

Nine mutants of Saccharomyces cerevisiae which are resistant to ketoconazole, have been isolated and characterized. In each case the mutation is nuclear in origin and allelic to a previously described mutation, erg3, which gives rise to a block in the delta 5-6 desaturation step of ergosterol biosynthesis. The significance of this second site mutation to the point of inhibitory action of ketoconazole, that is the P-450-mediated C-14 demethylation of lanosterol, is discussed.

The effects of azole and polyene antifungals on the plasma membrane enzymes of Candida albicans

The two clinically important classes of antimycotic drugs, the polyenes and azoles, act on the plasma membrane of the cell. The primary modes of action are believed to be through interaction with sterols (polyenes) and alteration in sterol composition of the membrane (azoles). In this report we show that, at growth inhibitory concentrations, the polyenes (nystatin and amphotericin) and azoles (miconazole and ketoconazole) also inhibit plasma membrane enzymes. There was extensive (greater than 75%) inhibition of the Candida albicans plasma membrane enzymes ATPase, glucan synthase, adenyl cyclase and 5'-nucleotidase, when assayed in situ. The antifungals papulacandin and echinocandin, which inhibit glucan synthesis, also inhibited plasma membrane enzymes in situ; glucan synthase (greater than 90%), 5'-nucleotidase (greater than 80%) and ATPase (70-80%). Purified plasma membrane was prepared from yeast cells of C. albicans by two different techniques: concanavalin A stabilization and coating of spheroplasts with silica microbeads. In the purified plasma membrane vesicles prepared from concanavalin A the adenyl cyclase and phosphodiesterase were extensively (greater than 90%) inhibited by the three different classes of antifungal drugs; variable inhibition was observed with ATPase (70-100%). The 3',5'-cyclic phosphodiesterase of the plasma membrane purified by the microbeads method was almost completely inhibited by all of the antifungals tested and there was partial inhibition of ATPase (20-85%) and adenyl cyclase (30-90%).

Effect of miconazole on growth and aflatoxin production by Aspergillus parasiticus

At 5 microM, miconazole prevented the growth of Aspergillus parasiticus Speare in a number of media. Sensitivity to miconazole was increased approximately 10-fold in a medium containing glycerol. At sub-inhibitory concentrations, miconazole stimulated aflatoxin synthesis on media which normally support toxin formation. Miconazole inhibited respiration and altered mitochondrial ultrastructure, suggesting that miconazole inhibits growth and stimulates aflatoxin production by depressing mitochondrial activity.

The genetics of medically important fungi

The present review is concerned with recent progress in basic genetic investigations with a variety of fungi which are pathogenic for man and animals. The principles and strategies involved in undertaking genetic investigations of sexual species and of asexual species are discussed. Progress in genetic analysis of Cryptococcus neoformans made possible by the discovery of its sexual phase is described in detail, as is progress in development of parasexual methods of analysis in Candida albicans. The genetic bases of virulence and drug resistance are discussed for those few species in which these phenotypes have been investigated. Suggestions for future research, including the application of recent advances in molecular biology to the study of pathogenic fungi, are presented.