Minimum Inhibitory Concentration (MIC) Assay

The MICs of 2Abz²³S²⁹ and ciprofloxacin (cip) were determined by broth microdilution assay, according to a previously reported protocol.17 In general, bacteria were grown overnight in LB for 24 h and were diluted to approximately 5 × 10⁵ colony-forming units (CFU/mL) in Mueller Hinton Broth (MHB, Difco, Becton Dickinson Co., Sparks, MD, USA). Then, 50 µL of the bacterial suspension was added to a 96-well U-bottom polystyrene microplate (Grainer, Germany) containing 50 µL of serially diluted peptides or antibiotics. The microplates were incubated at 37°C for 18 to 24 h. MICs were defined as the lowest concentration of the antimicrobial agent that entirely inhibited visible growth.