Fig. 1

Measuring drug responses in disk diffusion assays (DDAs) and in liquid broth microdilution assays (BMDAs). a diskImageR analysis measures pixel intensity corresponding to cell density, along 72 radii every 5°. The average radius (RAD) represents the distance in mm corresponding to the point where 20%, 50%, or 80% growth reduction occurs (light, medium, dark blue dots). The fraction of growth inside the zone of inhibition (FoG) is the area under the curve (red) at the RAD threshold, divided by the maximum area. b Range of FoG levels in 219 C. albicans clinical isolates. Red, blue, and green lines estimate high, medium, and low FoG levels, respectively. Unless otherwise specified, DDAs were performed using a single 25 µg FLC disk and analyzed after 48 h at 30 °C. c Comparison of FoG₂₀ and RAD₂₀ for the 219 isolates. d Illustration of MIC and supra-MIC growth (SMG) calculations. MIC₅₀ was calculated at 24 h as the FLC concentration at which 50% of the growth was inhibited, relative to growth in the absence of drug. SMG was calculated as the average growth per well above the MIC divided by the level of growth without drug. FLC was used in two-fold dilutions (0, 0.125 to 128 μg/ml). e Heatmaps illustrating OD₆₀₀ levels for concentrations below the MIC (yellow bar) in cyan and above the MIC in yellow for the isolates from Fig. 1c. Maps show OD₆₀₀ values at 24 and 48 h. f, g Effect of incubation time on RAD/MIC and FoG/SMG values. diskImageR analysis (f) and corresponding MIC and SMG levels (g) measured at 24 and 48 h for strains as in d. Of note, for truly drug-resistant strains such as T101 (MIC = 64, e), the small zone of inhibition makes FoG measurements less accurate than SMG levels. h RAD is concentration-dependent and FoG is concentration-independent as illustrated for strain SC5314 exposed to disks containing increasing concentrations of FLC (25, 50 and 300 µg) (left); RAD (middle) and FoG (right) levels for strains as listed. For all panels, n ≥ 2; ** P < 0.01; *P < 0.05