Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 23, 1998
Publication Date: N/A
Interpretive Summary: Salmonella transmission through eggs is of public health concern. Eggshells and eggshell membranes can be readily penetrated by bacteria including Salmonella. The egg is especially vulnerable in the first few seconds after lay, before the cuticle (a protein coating on the shell) hardens filling the pores. It is unclear what eggshell or membrane characteristics may best tslow such penetration. However, since the membranes have smaller openings than the shell they are generally thought to provide a more effective barrier against bacterial invasion. Pieces of eggshell membrane were used to determine the time needed for Salmonella to penetrate. A novel method to demonstrate bacterial penetration of a membrane was developed and reported. The same pieces of membrane were used to measure the density of the fibrous network of the membrane; these measurements were made on images collected with a confocal laser scanning microscope. Thus, an objective measure of membrane density is described. The amount of open space in the outer 8 um of eggshell membrane is not related to the time needed for Salmonella to penetrate.
Technical Abstract: Eggshell membrane was removed from ten broiler hatching eggs at approximately monthly intervals through the productive life of a commercial flock. A piece of membrane (2 x 2 cm) was used to cover an opening in an apparatus designed to test penetration by Salmonella typhimurium. The membrane was placed between two chambers as the only means of liquid transfer. The chamber above the membrane was filled with a suspension of S. typhimurium cells. Sampling of the bottom chamber provided cultural evidence of the penetration by a marker strain of S. typhimurium. Samples were drawn at 15 min., and 1, 3, 5, 7, 12, 24 and 48 hr. Following the cultural penetration experiment the same pieces of membrane were removed and stained for microscopic examination. Membrane structure was examined with the use of a confocal laser scanning microscope. Each image consisted of a composite of eight 1 um optical slices showing the fibers making up the outer surface of the membrane. These images were transferred to an image analysis software package that allowed the measurement of the inter-fiber area. No clear correlation could be made between the average size of all inter- fiber areas, or the total inter-fiber area measured in the outer 8 um of the outer membrane and the ability of S. typhimurium to penetrate the same piece of eggshell membrane.