Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/11/2006
Publication Date: 3/15/2007
Citation: Gast, R.K., Guraya, R., Bouldin, J.G., Holt, P.S., Moore, R.W. 2007.Colonization of specific regions of the reproductive tract and deposition at different locations inside eggs laid by hens infected with Salmonella enteritidis or Salmonella heidelberg. Avian Diseases.51:40-44.
Interpretive Summary: Public health authorities have been concerned for nearly twenty years that eggs containing Salmonella enteritidis in their edible liquid contents can transmit disease to humans and the Centers for Disease Control and Prevention have recently also reported a link between eggs and S. heidelberg infections in humans. Very substantial resources have already been invested in programs to detect and control S. enteritidis infections in commercial egg-laying flocks and FDA has proposed a national regulatory plan to address this problem in egg-laying flocks. Salmonella deposition inside eggs appears to result from the infection of reproductive organs (the ovary and oviduct) of laying hens, but little is know about how infection of specific regions of the reproductive tract affects the location of the resulting contamination inside eggs. In the present study, groups of laying hens were experimentally infected with large oral doses of S. heidelberg or S. enteritidis strains. The observed frequency of Salmonella colonization in infected hens was higher in the upper region of the reproductive tract (the ovary) than in lower regions of this tract (the oviduct), but the frequency of Salmonella isolation from eggs laid by these hens was not significantly different in the yolk or albumen. Therefore, there was no indication that any distinctive patterns of deposition in eggs were the result of corresponding patterns of infection of particular parts of the reproductive tract by individual Salmonella strains.
Technical Abstract: Internal contamination of eggs by Salmonella enteritidis has been a significant source of human illness for several decades and is the focus of a recently proposed FDA regulatory plan. Salmonella heidelberg has also been identified as an egg-transmitted human pathogen. The deposition of Salmonella strains inside eggs is apparently a consequence of reproductive tissue colonization in infected laying hens, but the relationship between colonization of specific regions of the reproductive tract and deposition in different locations within eggs is not well documented. In the present study, groups of laying hens were experimentally infected with large oral doses of S. heidelberg, S. enteritidis phage type 13a, or S. enteritidis phage type 14b. For all of these strains, the overall frequency of ovarian colonization (34.0%) was significantly higher than the frequency of isolation from either the upper (22.9%) or lower (18.1%) regions of the oviduct. No significant differences were observed between the frequencies of Salmonella isolation from egg yolk and albumen (4.0% and 3.3%, respectively). Some significant differences between Salmonella strains were observed in the frequency of isolation from eggs, but not in the frequency or patterns of isolation from reproductive organs. Accordingly, although the ability of these Salmonella strains to colonize different regions of the reproductive tract in laying hens was reflected in deposition in both yolk and albumen, there was no indication that any specific affinity of individual strains for particular regions of this tract produced distinctive patterns of deposition in eggs.