• The fungicide fludioxonil antagonizes fluconazole activity in the human fungal pathogen Candida albicans.

      Buschart, Anna; Burakowska, Anna; Bilitewski, Ursula; Biological Systems Analysis, Helmholtz Centre for Infection Research, Braunschweig, Germany. (2012-12)
      The fungicide fludioxonil is widely used in agriculture. Residua of this fungicide are occasionally detected in fruits and can therefore be ingested by humans. The human fungal pathogen Candida albicans expresses the target of fludioxonil, Nik1p, a type III histidine kinase involved in stress response. Inhibition of yeast and hyphae growth was hardly observable after treatment of C. albicans SC5314 with fludioxonil. As a side effect, however, we observed a concentration-dependent induction of the expression of the genes CDR1 and CDR2, encoding ATP-binding cassette (ABC) transporters. This was independent of the presence of the target of fludioxonil as induction was also observed in a Δnik1 deletion mutant. Deletion of the CDR1 gene aggravated the inhibition of germ tube formation by fludioxonil, indicating that, in the wild-type, the fungicide was discharged from the cell by Cdr1p. Cdr1p is also known as a resistance factor of C. albicans against the commonly used antimycotic fluconazole. Thus, the effect of concurrent exposure to fludioxonil and known cargoes of ABC transporters on their extrusion and the growth of C. albicans was examined. Pre-incubation with fludioxonil decreased the export rate of rhodamine 6G. The resistance to fluconazole was increased by fludioxonil, independently of Nik1p. Therefore, exposure of C. albicans to fludioxonil may lead to increased resistance to fluconazole treatment.
    • A viability assay for Candida albicans based on the electron transfer mediator 2,6-dichlorophenolindophenol.

      Hassan, Rabeay Y A; Bilitewski, Ursula; Biological Systems Analysis Group, Helmholtz Centre for Infection Research, 38124 Braunschweig, Germany. (2011-12-01)
      Candida albicans is an opportunistic fungal pathogen with comparably high respiratory activity. Thus, we established a viability test based on 2,6-dichlorophenolindophenol (DCIP), a membrane-permeable electron transfer agent. NADH dehydrogenases catalyze the reduction of DCIP by NADH, and the enzymatic activity can be determined either electrochemically via oxidation reactions of DCIP or photometrically. Among the specific respiratory chain inhibitors, only the complex I inhibitor rotenone decreased the DCIP signal from C. albicans, leaving residual activity of approximately 30%. Thus, the DCIP-reducing activity of C. albicans was largely dependent on complex I activity. C. albicans is closely related to the complex I-negative yeast Saccharomyces cerevisiae, which had previously been used in DCIP viability assays. Via comparative studies, in which we included the pathogenic complex I-negative yeast Candida glabrata, we could define assay conditions that allow a distinction of complex I-negative and -positive organisms. Basal levels of DCIP turnover by S.cerevisiae and C. glabrata were only 30% of those obtained from C. albicans but could be increased to the C. albicans level by adding glucose. No significant increases were observed with galactose. DCIP reduction rates from C. albicans were not further increased by any carbon source.