In vitro susceptibility was assessed using the disc diffusion method. Briefly, the bacterial suspension in agarose solution was inoculated on BHI agar plates, and the gel was allowed to solidify completely at room temperature. Whatman filter discs with DMSO, ampicillin (Amp, 10 μg/disc), or EETC (5 μg, 10 μg/disc) were placed on the plates and cultured overnight at 37 °C and 5% CO2. Susceptibility was assessed using linear fitting of the squared radius (diameter in mm) of the inhibition zones. Ampicillin was used for comparing the assay results. DMSO (0.01%) was used as the control.