Submitted to: Poultry Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/15/2010
Publication Date: 8/1/2010
Citation: Gast, R.K., Jones, D.R., Anderson, K.E., Guraya, R., Guard, J.Y., Holt, P.S. 2010. In Vitro Penetration of Salmonella Enteritidis through Yolk Membranes of Eggs from Six Genetically Distinct Commercial Lines of Laying Hens. Poultry Science: 89:1732-1736. Interpretive Summary: Chickens infected with Salmonella Enteritidis can sometimes deposit this pathogen inside eggs, resulting in the transmission of diarrheal disease to consumers. Although Salmonella is not often initially deposited inside egg yolks, bacteria from the surrounding albumen might penetrate through the vitelline membrane that surrounds the yolk and begin rapid and extensive growth in the nutrient-rich interior yolk contents. Egg refrigeration halts both penetration and growth by bacteria, but many S. Enteritidis control programs allow unrefrigerated storage of eggs on farms for up to 36 hours after laying. The present study used a laboratory egg contamination model to assess the ability of an S. Enteritidis strain to penetrate into the yolk contents during 24 hours of incubation at 30° C in eggs from six genetically distinct lines of commercial laying hens. Penetration of S. Enteritidis inside yolks was observed in eggs from all six lines of hens, with one line allowing significantly more penetration than two other lines. The age of the hens when the eggs were laid did not affect the outcome. These results demonstrate that penetration of S. Enteritids to reach the yolk contents and multiply to more dangerous levels can occur during unrefrigerated storage of eggs from diverse lines of laying hens, although some differences between lines are apparent. This information reinforces the importance of prompt refrigeration of eggs for protecting consumers from egg-borne transmission of S. Enteritidis infections.
Technical Abstract: Although deposition of Salmonella Enteritidis inside yolks is less common than deposition in albumen or on the vitelline (yolk) membrane in naturally contaminated eggs laid by infected hens, bacterial migration into the yolk to reach its nutrient-rich contents could lead to extensive multiplication. The present study used an in vitro egg contamination model to assess the ability of small initial numbers of S. Enteritidis to penetrate the vitelline membrane and multiply inside yolks of eggs laid by six genetically distinct commercial lines of hens during 24 h of storage at 30° C. Eggs from each line were tested at four different hen ages by inoculation of approximately 100 cfu of S. Enteritidis onto the outside of the vitelline membranes of intact yolks in plastic centrifuge tubes and then adding back the albumen into each tube before incubation. Overall, the frequency of penetration of S. Enteritidis into the yolk contents of eggs from individual lines of hens ranged from 30% to 58% and the mean concentration of S. Enteritidis in yolk contents after incubation ranged from 0.8 to 2.0 log10 cfu/ml. For both of these parameters, values for one hen line were significantly higher than for two other lines, but no other differences were observed. Hen age did not have a significant effect on egg yolk penetration by S. Enteritidis. These results indicate that opportunities for the migration and growth of small initial numbers of S. Enteritidis to attain more dangerous levels inside contaminated eggs during storage at warm temperatures can sometimes vary between different lines of laying hens.