Bacterial penetration of the eggshell and shell membranes of the chicken hatching egg: A review

Bacteria, including human enteropathogens, can penetrate the outer structures of the egg. There are several mechanisms employed by bacteria to gain entry to the egg. The most likely area on the egg to be penetrated is the air cell end, especially when temperature differential and moisture are favorable. The natural defenses that an egg has against such attack are generally not adequate to completely protect the egg from bacteria. The implications and consequences of bacterial penetration of the shell and membranes are serious, including potential dissemination of human pathogens to the hatchery, grow-out flock, and final product. This paper reviews the mechanisms involved in bacterial penetration, methods used to detect penetration, and the stages of modern production which lend themselves to shell penetration and the subsequent potential contamination of many chicks.