Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/6/2012
Publication Date: 1/1/2013
Citation: Gast, R.K., Guraya, R., Guard, J.Y. 2013. Salmonella Enteritidis deposition in eggs after experimental infection of laying hens with different oral doses. Journal of Food Protection. 76(1):108-113.
Interpretive Summary: Salmonella Enteritidis (SE) contamination of eggs has been a significant source of disease transmission to humans for many years, caused by infected hens depositing SE inside eggs before they are laid. Governments and the poultry industry have devoted substantial resources to control this problem by testing egg-laying flocks and applying practices aimed at reducing the likelihood that contaminated eggs will reach consumers. However, effective application of disease control methods requires a comprehensive understanding of the process by which contaminated eggs are produced. In the present study, groups of laying hens were experimentally infected with different oral amounts (doses) of SE in order to investigate any dose effects on the frequency and location of contamination in eggs laid by these birds. With each 100-fold increase in the dose of SE that was given to hens, significantly more eggs were found to be internally contaminated. Also, at the largest dose used in the study, a shift toward more eggs having albumen contamination (in addition to or instead of yolk contamination) was seen. These results demonstrate that the effectiveness of important risk reduction practices such as refrigeration can be influenced by the dose of SE that laying hens are exposed to from their environment.
Technical Abstract: The continuing attribution of human Salmonella Enteritidis (SE) infections to internally contaminated eggs has necessitated the commitment of substantial public and private resources to SE testing and control programs in commercial laying flocks. Cost-effective risk reduction requires a detailed and comprehensive understanding of how SE infections in hens result in deposition of the pathogen inside eggs. The present study sought to resolve some incompletely defined aspects of the relationship between SE oral exposure dose levels in experimentally infected laying hens and the frequency and location of subsequent egg contamination. In two trials, groups of specific-pathogen-free hens were experimentally inoculated with oral doses of 104, 106, or 108 CFU of a phage type 4 SE strain. Eggs were collected 5-23 d PI, and the yolk and albumen of each egg were cultured separately to detect SE contamination. Larger oral doses of SE administered to hens were associated with significant increases in the frequencies of both yolk and albumen contamination. Moreover, SE was found in the albumen of a far higher proportion of contaminated eggs from hens given the largest dose than from the other two groups. SE contamination was detected in 0.9% of yolk and 0.2% of albumen samples after inoculation of hens with 104 CFU, 4.0% of yolk and 1.7% of albumen samples following inoculation with 106 CFU, and 6.5% of yolk and 10.8% of albumen samples after inoculation with 108 CFU. These results demonstrate that oral exposure doses of SE for laying hens significantly affect important parameters of egg contamination which could influence the efficacy of risk reduction practices such as refrigeration.