Summary. The chicken egg is an important source of nutrients. Furthermore, eggs have physical and biological defence mechanisms to protect the embryo against invasion and multiplication of micro-organisms. The egg shell and shell membranes physically obstruct microbial penetration of the egg, while the viscosity and pH of the egg white inhibit bacterial proliferation. The egg white also contains a number of proteins with demonstrated antimicrobial activities, such as bacterial cell lysis, metal binding, and vitamin binding, which are part of the natural defence system of the egg. Eggs are the subject of research aimed at identifying substances with biological functions beyond nutrition. Various biological functions of egg components, particularly antimicrobial activity, immunomodulating activity, and protease inhibition, underscore the importance of these substances in the prevention and treatment of human and animal diseases.

Key words: egg, antimicrobial defence system, lysozyme, immunoglobulin IgY, activities of biological substances