The present invention relates to an antibacterial composition containing, as an active ingredient, adenylate kinase or adenosine kinase (ADK) protein derived from Mycobacterium tuberculosis , and a composition for preventing or treating infectious diseases. In addition, the present invention relates to a composition for preventing or treating sepsis or septic shock, the composition containing, as active ingredients, the ADK protein and an antibiotic agent. The ADK protein derived from Mycobacterium tuberculosis according to the present invention has excellent antibacterial activity selectively against gram-negative bacteria, and thus can be favorably used as an antibacterial composition against gram-negative bacteria or for the prevention or treatment of infectious diseases caused by gram-negative bacteria. In addition, the ADK protein according to the present invention has excellent effects of inhibiting bacterial proliferation and eliminating endotoxin isolated from dead bacteria, thereby minimizing side effects caused by antibiotic agents when used in combination with the antibiotic agents, and has a significantly excellent sepsis treatment effect compared with single administration, thus can be favorably used for the prevention or treatment of sepsis or septic shock.