In Vitro Penetration of Egg Yolks by Salmonella Enteritidis and Salmonella Heidelberg Strains During 36-hour Ambient Temperature Storage

Authors: Gast, Richard; Guraya, Rupinder - Rupa; Guard, Jean; Holt, Peter

Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/7/2007
Publication Date: 7/1/2007
Citation: Gast, R.K., Guraya, R., Bouldin, J.G., Holt, P.S. 2007. In Vitro Penetration of Egg Yolks by Salmonella Enteritidis and Salmonella Heidelberg Strains During 36-hour Ambient Temperature Storage. Poultry Science.86(7):1431-1435

Interpretive Summary: Eggs that contain Salmonella in their edible contents can transmit diarrheal disease to consumers. Although chickens infected with Salmonella do not deposit this pathogen inside egg yolks very often, bacteria from the surrounding albumen might penetrate through the membrane that surrounds the yolk, resulting in rapid and extensive Salmonella growth in the nutrient-rich interior contents of the yolk. Egg refrigeration halts both penetration and growth by bacteria, but a proposed national S. enteritidis control program would allow unrefrigerated storage of eggs on farms for up to 36 hours. The present study used a laboratory egg contamination model to assess the ability of S. enteritidis or S. heidelberg strains to penetrate through the yolk membrane and multiply inside yolks during 36 hours of incubation at warm temperatures. All Salmonella strains were able to penetrate the yolk membrane and most strains grew to significantly higher levels during incubation at 30' C, but significantly less penetration and growth were observed at 20' C. The S. enteritidis strains penetrated and multiplied inside yolks significantly more than did the S. heidelberg strains, and differences were also sometimes evident between individual strains. These results demonstrate that controlling ambient temperatures during pre-refrigeration storage may be an important adjunct to prompt refrigeration for limiting Salmonella growth in eggs and thereby for preventing egg-transmitted human illness.

Technical Abstract: Although Salmonella deposition inside egg yolks is uncommon, migration through the vitelline membrane into the nutrient-rich yolk contents could enable rapid bacterial multiplication. Egg refrigeration restricts both penetration and growth, but a recently proposed national S. enteritidis control program would allow unrefrigerated temperature storage of eggs on farms for up to 36 hours. The present study used an in vitro egg contamination model to assess the ability of S. enteritidis and S. heidelberg strains to penetrate the vitelline membrane and multiply inside yolks during 36 hours of storage at either 20' or 30' C. All Salmonella strains penetrated the yolk membrane (at a mean frequency of 45%) and most strains grew to significantly higher levels (with a mean log10 bacterial concentration of 2.2 cfu/mL) during incubation at 30' C. Significant differences in penetration frequency and yolk multiplication were observed between individual strains and between serotypes (S. enteritidis > S. heidelberg for both parameters). Penetration and multiplication were significantly less frequent during incubation at 20' C. These results demonstrate that controlling ambient temperatures during pre-refrigeration storage may be an important adjunct to prompt refrigeration for limiting Salmonella growth in eggs and thereby for preventing egg-transmitted human illness.