GROWTH OF SALMONELLA-ENTERITIDIS (SE) IN EGG CONTENTS FROM HENS VACCINATED WITH AN SE BACTERIN

Vaccination of hens with Salmonella enteritidis (SE) bacterin has beco me an important industry management tool to reduce both the incidence of SE in flocks and the production of SE-contaminated eggs. After vacc ination, antibodies to SE can be found in both the serum and egg yolks . The current study was undertaken to examine whether the antibodies d eposited in eggs after vaccination would have any effect on the in vit ro growth of 10 SE seeded into pooled egg contents and incubated at 37 degrees C for 24 h. The SE inoculum grew well in egg contents from co ntrol-vaccinated hens, and a high percentage of these samples were cul ture positive for SE. Conversely, significantly fewer egg contents fro m vaccinated hens were positive for SE at weeks 2, 3, 4, and 5 post-pr imary vaccination and weeks 1, 2, and 4 post-secondary vaccination. Af ter 24 h incubation, the SE inoculum grew to 10(8)-10(9) organisms ml( -1) in egg contents from control hens, while growing to less than 10(4 ) organisms ml(-1) in egg contents from vaccinated hens. No inhibition of growth was observed for a second organism, Proteus mirabilis, in e gg contents from bacterin-vaccinated hens, indicating antigen-specific ity of the activity. Inhibition of SE growth was observed in egg conte nts from vaccinated hens diluted 1:5 in eggs from control hens. Mixed results were observed for egg contents receiving a 10-fold higher SE i noculum with significant inhibition of growth observed in one trial an d minimal inhibition observed in a second trial. Supplementing the egg samples with an iron source abrogated the inhibition, suggesting that the iron-restricted environment found in eggs may play a role in the observed inhibition. (C) 1996 Academic Press Limited