Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2011
Publication Date: 6/1/2011
Citation: Gast, R.K., Guraya, R., Guard, J.Y., Holt, P.S. 2011. The relationship between the numbers of Salmonella Enteritidis, Salmonella Heidelberg, or Salmonella Hadar colonizing reproductive tissues of experimentally infected laying hens and deposition inside eggs. Avian Diseases. 55:243-247. Interpretive Summary: The transmission of disease to humans by eggs contaminated with Salmonella Enteritidis in their edible liquid contents remains a leading public health problem. A link between egg consumption and human S. Heidelberg infections has also been reported. Very substantial public and private resources have already been committed to programs for the detection and control of S. Enteritidis in commercial egg-laying flocks and a national regulatory plan has recently been instituted by FDA. The deposition of Salmonella inside eggs is a result of infection spreading to reproductive organs (the ovary and oviduct) of laying hens, but little is know about how whether the number of Salmonella cells that reach these organs influences the likelihood of egg contamination. In the present study, groups of laying hens were experimentally infected with large oral doses of strains of S. Enteritidis S. Heidelberg, or S. Hadar. Significantly more contaminated eggs were laid by hens infected with S. Enteritidis than with S. Heidelberg, and no egg contamination was associated with S. Hadar infection. However, no significant differences were observed in the numbers of the three Salmonella strains which colonized either the ovary or oviduct. Although the ability of Salmonella strains to colonize the reproductive tract in laying hens was reflected in deposition inside eggs in this study, neither the presence nor level of Salmonella colonization in reproductive tissues consistently predicted the likelihood of egg contamination.
Technical Abstract: Contamination of eggs by Salmonella Enteritidis has been a prominent cause of human illness for several decades and is the focus of a recently implemented national regulatory plan for egg-producing flocks in the United States. S. Heidelberg has also been identified as an egg-transmitted pathogen. The deposition of Salmonella strains inside eggs is a consequence of reproductive tract colonization in infected laying hens, but prior research has not determined the relationship between the numbers of Salmonella that colonize reproductive organs and the associated frequency of egg contamination. In the present study, groups of laying hens in two trials were experimentally infected with large oral doses of strains of S. Enteritidis (phage type 13a), S. Heidelberg, or S. Hadar. Reproductive tissues of selected hens were cultured to detect and enumerate Salmonella at 5 days postinoculation and the interior contents of eggs laid between 6 and 25 days postinoculation were tested for contamination. Significantly more internally contaminated eggs were laid by hens infected with S. Enteritidis (3.58%) than with strains of either S. Heidelberg (0.47%) or S. Hadar (0%). However, no significant differences were observed between Salmonella strains in either the frequency or numbers of isolation from ovaries or oviducts. Salmonella isolation frequencies ranged from 20.8% to 41.7% for ovaries and from 8.3% to 33.3% for oviducts. Mean Salmonella colonization levels ranged from 0.10 to 0.51 log cfu/g for ovaries and from 0.25 to 0.46 log cfu/g for oviducts. Although parallel rank-orders were observed for Salmonella enumeration (in both ovaries and oviducts) and egg contamination frequency, a statistically significant relationship could not be established between these two parameters of infection.