ARS | Publication request: Penetration of Salmonella enteritidis and S. heidelberg strains into egg yolks during 36 hour ambient temperature storage

Submitted to: International Association for Food Protection
Publication Type: Abstract
Publication Acceptance Date: February 25, 2007
Publication Date: July 15, 2007
Citation: Gast, R.K., Guraya, R., Bouldin, J.G., Holt, P.S. 2007. Penetration of Salmonella enteritidis and S. heidelberg strains into egg yolks during 36 hour ambient temperature storage. International Association for Food Protection, p 99.

Technical Abstract: Although Salmonella deposition inside yolks is uncommon in naturally contaminated eggs, 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 ambient 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 small numbers of four S. enteritidis strains and four S. heidelberg strains to penetrate the vitelline membrane and multiply inside yolks during 36 hours of storage at either 20' or 30' C. After inoculation onto the exterior surface of the vitelline membrane, all eight Salmonella strains penetrated to the yolk contents (at a mean frequency of 45.1%) 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.