Antimicrobial activity of LysAB1245

The minimum inhibitory concentration (MIC) of LysAB1245 was determined using the broth microdilution method, according to the Clinical and Laboratory Standard Institute (CLSI) guidelines [31]. Briefly, a single colony of 20 clinical MDR A. baumannii isolates belonging to KL 2, 3, 6, 10, 47, 49, and 52 and A. baumannii ATCC 19606 was grown in Mueller-Hinton broth (MHB; Difco) and incubated at 37°C with shaking until the cells reached the logarithmic phase. Endolysin LysAB1245 (134.71 μg/mL) was serially diluted (1:2) in microtiter plate (50 μL/well). Subsequently, 50 μL of A. baumannii culture with approximately 10⁶ colony-forming units (CFU/mL) was inoculated to the microplate, containing different diluted LysAB1245 and further incubated at 37°C for 18 h. MIC was defined as the of the antibacterial agent that inhibited the visible growth of bacteria, while minimal bactericidal concentration (MBC) was defined as the lowest concentration of the antibacterial agent required to kill bacteria. The experiment was performed in triplicate in two independent experiments.