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Athens Study Examines Salmonella Contamination of Eggs

11 January 2013

US - The number of Salmonella consumed by hens affected the number of Salmonella-positive eggs, report researchers from Athens, Georgia. At the highest dose, 6.5 per cent of the yolks and 10.8 per cent of the albumen sampled were positive for Salmonella enteritidis.

Oral-exposure doses of Salmonella Enteritidis for laying hens can significantly affect both the frequency and location of deposition of this pathogen inside eggs, according to new research from USDA ARS Egg Safety and Quality Research Unit at the Russell Research Center in Athens, Georgia.

Writing in Journal of Food Protection, Richard K. Gast and co-authors say that the continuing attribution of human Salmonella Enteritidis infections to internally contaminated eggs has necessitated the commitment of substantial public and private resources to Salmonella Enteritidis testing and control programmes in commercial laying flocks.

Cost-effective risk-reduction requires a detailed and comprehensive understanding of how Salmonella Enteritidis infections in hens result in deposition of the pathogen inside eggs.

Their study sought to resolve some incompletely defined aspects of the relationship between Salmonella Enteritidis oral-exposure dose levels in experimentally infected laying hens and the frequency and location of subsequent egg contamination. In two trials, groups of specific-pathogen-free hens were experimentally inoculated with oral doses of 104, 106, or 108 colony-forming units (CFU) of a phage type 4 Salmonella Enteritidis strain.

Eggs were collected five to 23 days post-inoculation, and the yolk and albumen of each egg were cultured separately to detect Salmonella Enteritidis contamination.

Larger oral doses of Salmonella Enteritidis administered to hens were associated with significant increases in the frequencies of both yolk and albumen contamination. Moreover, Salmonella Enteritidis was found in the albumen of a far higher proportion of contaminated eggs from hens given the largest dose than from the other two groups.

Salmonella Enteritidis contamination was detected in 0.7 per cent of yolk and 0.2 per cent of albumen samples after inoculation of hens with 104 CFU, 4.0 per cent of yolk and 1.7 per cent of albumen samples after inoculation with 106 CFU, and 6.5 per cent of yolk and 10.8 per cent of albumen samples after inoculation with 108 CFU.


Gast, R.K., R. Guraya and J. Guard. 2013. enteritidis deposition in eggs after experimental infection of laying hens with different oral doses. Journal of Food Protection, Number 1, January 2013, pp.4-183, pp. 108-113(6). DOI:

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