Currently, the bacterial etiology infectious diseases still remain a global health problem. Most of them are caused by gram-negative pathogenic microorganisms. The traditional method of infectious diseases treatment is based on the use of antibiotics. However, the rapid development of the resistance of pathogenic microorganisms to existing antibiotics forces to seek alternatives to traditional therapy. One of such alternatives is the therapy with bacteriophage endolysins - bacteriolytic enzymes capable of destroying the bacterial cell wall by hydrolyzing the peptidoglycan. Endolysins are highly specific for certain pathogens. The main limitation of their use towards gram- negative bacteria is the presence of an outer membrane in the latter preventing the penetration of lytic enzyme to its substrate. The effectiveness of endolysin penetration can be increased by destabilizing the outer membrane of gram-negative bacteria