The egg is a complex formation that allows the development of an embryo ex utero by providing essential nutrients and a molecular protective system. In addition to immunoglobulins, molecular defences of the egg are also composed of antimicrobial peptides/proteins that are predominantly localized in egg white (EW). The present study investigated whether this innate antimicrobial protection is stimulated by the degree of contamination of the hen milieu by using two experimental models. Firstly, we compared the global antimicrobial activity of EW issued from hens reared in extreme bacterial environments: bacterial free (axenic, Ax), specific pathogen free (SPF) and standard (ST) conditions. EW issued from the ST and SPF groups demonstrated a greater inhibitory effect against Staphylococcus aureus as compared to those of Ax groups (9.8% and 4% respectively, P<0.05). The second approach explored the effect of an immune challenge in hens on the antimicrobial potential of EW. EW from hens stimulated with Salmonella Enteritidis lipopolysaccharide showed greater antimicrobial activity against Staphylococcus aureus (14.8%, P