Determination of Minimum Inhibitory Concentrations

All compounds were purchased from Sigma-Aldrich (MO, United States). To determine the minimum inhibitory concentrations (MIC), the broth-dilution method was applied, as standardized by the Clinical Laboratory Standards Institute (CLSI 2012), with minor adjustments. Briefly, bacteria that had been grown for 16 h, 28°C in LB were normalized to 1 × 108 colony forming units (CFU) mL^–1 with fresh liquid LB. Then, 190 μL of LB containing twofold serial dilutions of each of the tested compounds were inoculated with 10 μL of bacterial suspension containing 1 × 106 CFU in 96-well microtiter plates for 24 h, 28°C with continuous shaking at 150 rpm. The MIC was recorded as the lowest concentration of compound that was able to inhibit the visible growth of bacteria.