Importance of antibacterial proteins in egg white as a function of hen age
There are two main mechanisms of egg contamination: vertical transmission during eggshell formation in the oviduct, and horizontal transmission (trans-shell penetration) that occurs following oviposition. Bacteria that pass through the eggshell and associated membranes reach the egg white (albumen), which is an unfavourable medium for bacterial growth and mobility due to its high viscosity, high pH and potent antimicrobial proteins. The antimicrobial activities of protective proteins can act either through direct interaction with the bacterial cell wall (lysozyme, avian beta-defensins) or indirectly by decreasing the bioavailability of growth factors such as iron (ovotransferrin) or biotin (avidin). A new study presents comprehensive in vitro and in ovo analyses of the importance and effectiveness of egg white antimicrobial properties against bacterial contamination.
The results show that concentrations of egg white proteins, particularly ovotransferrin, are a critical factor to prevent bacterial survival in egg white. This egg white inhibitory activity is proportional to the ovotransferrin content in egg white. Additionally, this study showed that the ability of egg white to inhibit bacterial growth also depends on the initial bacterial load, varying from bactericidal at low inoculum to bacteriostatic as the inoculum concentration increases. The results also demonstrate that although the egg white has potent antimicrobial properties, the capacity of egg white to prevent bacterial growth is limited by the concentration of antimicrobial proteins for a given initial bacterial load, and that these characteristics strongly depends on hen age. The concentrations of lysozyme and ovotransferrin increased with hen age, and eggs laid by older hens exhibited the greatest potential to prevent the growth of the highest Salmonella inoculum.
