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. Furthermore, the present invention relates to a method for preventing, improving or treating an infectious disease comprising administering the present antibacterial composition. 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 has an excellent sepsis treatment effects, thus can be favorably used for the prevention or treatment of sepsis or septic shock.