Submitted to: Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/8/1996
Publication Date: N/A
Interpretive Summary: A number of human outbreaks of Salmonella enteritidis (SE) have been linked to the consumption of SE-contaminated eggs. This has had a major impact on the confidence of the general public in the egg as a safe food product and on the economics of the egg industry. The incidence and number of SE found in eggs is very low. However, improper handling of eggs by the consumer can result in the increase of SE numbers to dangerou levels, increasing the potential for food poisoning. We have found that antibodies against SE deposited in the egg yolk during immunization of hens with a killed SE vaccine can inhibit the growth of SE in eggs by at least 24 hours. Following incubation, the SE can attain numbers approaching 100 million/ml in normal egg contents but less than 10 thousand/ml in eggs from vaccinated hens. The inhibition can still be seen when the eggs are diluted 1:5 in nonimmune egg but is not seen when high numbers of SE are present. These results indicate that vaccination of hens against SE, besides helping protect hens against infection, can also help protect egg consumers by reducing the numbers of SE that may be present in their food following inadvertent food abuse during preparation.
Technical Abstract: Vaccination of hens with a Salmonella enteritidis (SE) bacterin has become an important industry management tool to reduce both the incidence of SE in flocks and the production of SE-contaminated eggs. Following vaccination, antibodies to SE can be found in both the serum and egg yolks. The current study was undertaken to examine whether the antibodies s deposited in eggs following vaccination would have any effect on the in vitro growth of 10 SE seeded into pooled egg contents and incubated at 37C for 24 hours. The SE inoculum grew well in egg contents from sham- vaccinated control hens and a high percentage of these samples were culture positive for SE. Conversely, significantly fewer egg contents from vaccinated hens were positive for SE at weeks 2,3,4, and 5 post- primary vaccination and weeks 1,2, and 4 post secondary vaccination. Following 24 hours incubation, the SE inoculum grew to 100 million organisms/ml in egg contents from control hens while growing to less than 10 thousand organisms/ml in egg contents from vaccinated hens. No inhibition of growth was observed for a second organism, Proteus mirabilis, indicating antigen-specificity of the activity. Inhibition of SE growth was observed in egg contents from vaccinated hens diluted 1:5 in egg from control hens. Mixed results were observed for egg contents receiving a 10-fold higher SE inoculum. Supplementing the egg samples with an iron source abrogated the inhibition.