Fig 6.

Doxycycline synergizes with fluconazole via iron sequestration. (A) Cells of C. albicans SC5314 were spotted onto SD plates containing combinations of fluconazole and doxycycline at standard concentrations, with and without ferric citrate or ferric chloride added at the indicated concentrations. Plates were incubated for 2 days before being scanned. (B) Cells of S. cerevisiae BY4742 were similarly spotted onto SD plates. Plate scans were taken after 2 days. (C) Colorimetric assessment of iron-chelating activity of doxycycline, tetracycline, and fluconazole. Iron chelation is expressed as a reduction of absorbance at 630 nm. Filled circles, doxycycline; open circles, tetracycline; filled squares, fluconazole; open squares, water. Mean values with standard deviations from three independent experiments are shown. (D) Cells of C. albicans SC5314 were spotted onto SD plates containing combinations of fluconazole (10 μg/ml) and BPS (20 μg/ml). Plates were incubated for 4 days before being scanned.