Tetracycline alters drug susceptibility in Candida albicans and other pathogenic fungi

Abstract

The tetracycline (TET) promoter has been used in several systems as an inducible regulator of gene expression. In control analyses, the standard Candida albicans laboratory strain SC5314 was found to have altered susceptibility to a variety of antifungal drugs in the presence of relatively high concentrations (50-200 mg ml "1 ) of TET. Altered susceptibility was most notable with exposure to amphotericin B (AMB), with a 32-fold increase in susceptibility, and terbinafine (TRB), with a 32-fold decrease in susceptibility. The TET/AMB synergy was observed in several clinical isolates of C. albicans and in the distantly related species Aspergillus fumigatus and Cryptococcus neoformans. The TET/AMB synergy is not related to efflux pump activity, as determined by FACS analyses and by analysis of a strain containing efflux pump deletions. Gene expression analyses by luciferase and by quantitative real-time reverse transcriptase PCR failed to identify significant alterations in expression of any genes associated with resistance. C. albicans grown with TET for 48 h does show a reduction in total cellular ergosterol. Analysis of growth curves suggests that the TET effect is associated with lack of a diauxic shift, which is related to a loss of mitochondrial function. MitoTracker fluorescent dye was used to demonstrate that TET has a direct effect on mitochondrial function. These results demonstrate the need for careful analysis of TET effects when using a TET-inducible promoter, especially in studies that involve antifungal drugs. This study defines some limits to the use of the TET-inducible promoter, and identifies effects on cells that are the result of TET exposure alone, not the result of expression of a targeted gene.

Mitochondria and Fungal Pathogenesis: Drug Tolerance, Virulence, and Potential for Antifungal Therapy

“…Mitochondrial mutants of C. glabrata are more sensitive to amphotericin B (9, 86). Decreased susceptibility to this drug was also observed for C. albicans treated with tetracycline; this was attributed to the effects of tetracycline on the function of mitochondria (66). Tetracycline also increased the sensitivity to amphotericin B of C. neoformans and Aspergillus fumigatus (66), implying that mitochondrial roles in polyene tolerance are broadly conserved in pathogenic fungi.…”

“…Decreased susceptibility to this drug was also observed for C. albicans treated with tetracycline; this was attributed to the effects of tetracycline on the function of mitochondria (66). Tetracycline also increased the sensitivity to amphotericin B of C. neoformans and Aspergillus fumigatus (66), implying that mitochondrial roles in polyene tolerance are broadly conserved in pathogenic fungi. Moreover, a large study by Hillenmeyer et al that included 1,144 chemical genomic assays in S. cerevisiae found a significant enrichment in the GO (Gene Ontology) terms "mitochondrial inheritance," "mitochondrial localization," and "mitochondrial distribution" among genes required for wild-type fitness in the presence of nystatin (38).…”

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

“…Mitochondrial membrane potential was evaluated using the fluorescent probes rhodamine 123 and MitoTracker green (Invitrogen) (60,61), according to the manufacturer's recommendations. Yeasts were grown in Sabouraud liquid medium as described above and suspended at 10 7 cells/ml.…”

In Vitro Analysis of Finasteride Activity against Candida albicans Urinary Biofilm Formation and Filamentation

“…FLC indirectly inhibits ergosterol synthesis by the inhibition of microsomal cytochrome P450, whereas AMB interacts directly with ergosterol in the plasma membrane. Additionally, recent publications (37)(38)(39)(40)(41)(42) have suggested that the antifungal activity of AMB might also be mediated by oxidative damage. …”