Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/6/2006
Publication Date: 6/1/2006
Citation: Gast, R.K., Holt, P.S., Guraya, R. 2006. Effect of egg refrigeration on in vitro penetration of salmonella enteritidis through the egg yolk membrane. Journal of Food Protection. 69:1426-1429
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. The present study used a laboratory egg contamination model to assess the ability of S. enteritidis to penetrate through the yolk membrane during storage at different combinations of warm and refrigerated temperatures. Immediate refrigeration prevented the bacteria from penetrating through the yolk membrane to reach the nutrient-rich yolk contents. However, as storage time at a warm temperature before refrigeration increased, so did the frequency at which S. enteritidis penetrated inside the yolks. These results support an emphasis on prompt refrigeration of eggs in Salmonella control programs to minimize the risk that pathogens will grow to higher (and more dangerous) levels after penetrating into the yolks of contaminated eggs.
Technical Abstract: Internally contaminated eggs have been implicated as leading sources of transmission of Salmonella enteritidis to humans. Although S. enteritidis is not often deposited inside the nutrient-rich yolks of naturally contaminated eggs, penetration through the vitelline membrane to reach the yolk contents could result in rapid bacterial multiplication. Previous studies have observed such penetration to occur at moderately low frequencies at warm temperatures using in vitro egg contamination models. The present study determined whether egg refrigeration affects the frequency of in vitro penetration of S. enteritidis across the yolk membrane. After inoculation of small numbers of S. enteritidis onto the outside of the vitelline membranes of intact yolks, immediate refrigeration of contaminated samples prevented the penetration of S. enteritidis into the egg yolk contents. However, S. enteritidis penetrated inside the yolk contents in 4% of contaminated egg samples refrigerated after 2 h of storage at 30' C, 15% of samples refrigerated after 6 h of storage at 30' C, and 40% of samples stored at 30' C for 24 h. These results highlight the value of prompt refrigeration for restricting the opportunities for S. enteritidis to multiply to high levels inside the yolks of contaminated eggs.