Bacterial Contamination on the Shell Surface of Hen Eggs and the Source of Contamination

Abstract

The source of bacterial contamination on the shell surface of hen eggs on the farm was examined. No bacteria were detected on the shell surface of 55 (92%) out of 60 eggs obtained aseptically from the oviduct of old hens. On the shell surface of eggs taken just after being laid in disinfected cages an average of 10⁴ CFU bacteria/egg were detected. On the shell surface of eggs, which were laid in commercial cages and carried to the front of the egg washer on transporting equipment an average of 10⁵ CFU bacteria/egg were detected.
As a supplementary experiment, shell eggs carefully washed, disinfected, and dried, were transported on three conveyers and a lifter. The surface of these eggs were contaminated with 10³-10⁴ CFU bacteria/egg on each equipment.
Large numbers of bacteria were detected on egg conveyers and egg lifter on the farm by the swab test. Large numbers of bacteria were also detected in the air on the farm. Smaller numbers of bacteria were detected on the equipment and the air of the GP center (packing station) neighboring the farm. Bacteria isolated from the shell surface of eggs, egg transporting equipment, and the air were mainly gram positive bacteria such as Micrococcus and Staphylococcus.
In conclusion, the degree of bacterial contamination on the shell surface of eggs when they were laid was small, but the contamination from equipment and the air during transport was very important.