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A study to examine the egg-to-egg variations in the growth of Salmonella spp. in egg contents

Project Code: B03015

01/11/2012

University of Bristol
Humphrey, T

The aim of this study was to identify the factors that allow Salmonella Enteritidis to survive and multiply within the egg and to compare these to other serovars of Salmonella.

Salmonella Enteritidis was found to have a number of abilities that allow survival in the albumen and movement into the yolk of the egg allowing growth to a high level, frequently greater than one billion bacteria per egg. Firstly, it was able to survive well in the albumen at hen body temperature. It could also use the glucose present in fresh eggs as an energy source and to make the albumen less alkaline, and so more suitable for bacterial growth.

Work on bacterial surface structures showed that bacteria must be able to move in order to multiply in the egg, and that adhesive surface structures, fimbriae, are used by Salmonella to attach to, and enter, the yolk. The combination of certain surface structures and the ability to survive in the albumen shown by S. Enteritidis is not shared by other Salmonella serovars that have been widespread in the past, such as serovars Gallinarum, Pullorum and Typhimurium.

High levels of glucose and a low capacity of the iron-binding proteins in the albumen were factors that were found to be linked to high levels of bacterial growth. Iron-binding capacity was found to vary significantly between individual hens, raising the possibility of selecting hens that lay eggs with a high capacity for binding iron, and so resist bacterial growth. The composition of the albumen is known to vary between breeds of hen, and this is an area which merits further investigation.

Final report

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