ARS | Publication request: Multiplication of Salmonella Enteritidis on Egg Yolk Membranes and Penetration into Yolk Contents

Submitted to: International Association for Food Protection
Publication Type: Abstract
Publication Acceptance Date: March 15, 2008
Publication Date: August 4, 2008
Citation: Gast, R.K., Guraya, R., Bouldin, J.G., Holt, P.S. 2008. Multiplication of Salmonella Enteritidis on egg yolk membranes and penetration into yolk contents. International Association for Food Protection Proceedings, p.35.

Technical Abstract: Prompt refrigeration to limit bacterial multiplication is a critical aspect of efforts to control the transmission of Salmonella enterica serovar Enteritidis (S. Enteritidis) to consumers of contaminated eggs. However, a proposed national S. Enteritidis control program would allow unrefrigerated ambient temperature storage of eggs on farms for up to 36 hours. Although the nutrient-rich yolk interior is an uncommon location for S. Enteritidis contamination in freshly laid, naturally contaminated eggs, migration across the vitelline membrane could lead to rapid bacterial multiplication inside eggs even when the initial site of deposition is outside the yolk. The objective of the present study was to determine whether bacterial multiplication can also occur on the egg yolk membrane (before or in addition to multiplication within the yolk contents) and thereby further increase the risk for consumers. Using an in vitro egg contamination model, four strains of S. Enteritidis were inoculated onto the exterior surface of yolk membranes and their ability to either multiply in association with the yolk membrane or migrate through that membrane to reach the yolk contents was assessed during 36 h of incubation at 30'C. All four S. Enteritidis strains penetrated the vitelline membrane to reach the yolk contents (at an overall frequency of 11.5%) during the first 12 h of incubation. The mean log10 concentration of S. Enteritidis was significantly higher in whole yolks (including yolk membranes) than in yolk contents at both 12 h (0.818 vs. 0.167 CFU/ml) and 36 h (2.767 vs. 1.402 CFU/ml) of incubation. These results demonstrate that S. Enteritidis multiplication on the vitelline membrane may both precede and exceed multiplication resulting from penetration into the yolk contents during the first 36 h of unrefrigerated storage, further documenting the importance of rapid refrigeration for protecting consumers from egg-transmitted illness.