Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/2004
Publication Date: 4/1/2005
Citation: Murase, T., Holt, P.S., Gast, R.K. 2005. Growth of salmonella enterica serovar enteritidis in albumen and yolk contents of eggs inoculated with this organism onto the vitelline membrane. Journal of Food Protection. 68(4):718-721.
Interpretive Summary: Salmonella enteritidis remains a serious food poisoning problem for the US consumer. Generally, there are very few S. enteritidis organisms contaminating the eggs at lay but these numbers can increase to dangerous levels if the eggs are allowed to sit unrefrigerated for long periods. The current study was conducted to investigate whether 1) S. enteritidis deposited near the yolk membrane can penetrate the membrane and replicate in the yolk and 2) how well do these organisms grow in the albumen and does location in relation to the yolk membrane exert an effect. We found penetration into the yolk contents in only a small percentage of the samples kept at room temperature (25C) but a high percentage of the albumens remained positive at 6 days post inoculation with counts of S. enteritidis in some samples reaching more than 430 million. A high percentage of albumen samples kept at 4C contained detectable S. enteritidis but the numbers of organisms were much lower. These results indicate that the location of where the S. enteritidis is deposited in the egg is important as is the temperature in which the eggs are stored.
Technical Abstract: By using an in vitro model simulating the potential'opportunities for Salmonella enterica serovar Enteritidis (Salmonella Enteritidis) to proliferate within eggs contaminated with this organism following oviposition, growth of Salmonella Enteritidis in eggs was investigated. One hundred CFU of one of three Salmonella Enteritidis strains originating either from egg contents, chicken meat, or a human infection were experimentally inoculated onto the vitelline membrane of eggs collected from specific-pathogen-free (SPF) flocks of chickens and incubated at 25C. Salmonella Enteritidis organisms were detected in 8% of yolk contents of the eggs inoculated with any of the test strains attaining Salmonella Enteritidis levels ranging from 2.0 x 102 to 4.2 x 108 CFU/ml by day 6. The organisms were also detected in the albumen from 38 of 55 eggs tested growing to levels ranging from 1.0 x 102 to 4.3 x 108 CFU/ml by day 6 post inoculation. An additional 3 yolk contents and 15 albumen samples were culture positive for Salmonella Enteritidis following enrichment. There was no correlation between the number of the organisms in the yolk contents and that in the albumen from each of the eggs. When 102 CFU of the egg strain was inoculated into samples of separated albumen obtained from eggs that were stored at 4C for 1 to 4 weeks or at 25C for 1 week, slight growth (3.0 x 102 to 7.4 x 103 CFU/ml) was found in only 3 of the 60 albumen samples by day 6 post inoculation, but the organisms were recovered from 52 samples following enrichment. The results suggest that the environment on or near the vitelline membrane can be conducive to Salmonella Enteritidis proliferation over time.