Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 15, 1999
Publication Date: April 15, 2000
Interpretive Summary: Salmonella enteritidis (SE) contamination of egg contents is an important source of food-borne transmission of disease to humans. Refrigeration can prevent small numbers of SE in eggs from growing to more dangerous levels. Because bacteria grow much more rapidly in egg yolk than in albumen, the location at which SE cells are deposited is critical for determining how quickly refrigeration must lower internal egg temperatures. In this study, groups of laying hens were experimentally infected with SE strains of different phage types. For all 3 strains used, eggs laid by infected hens were more often contaminated in the yolk (2.5% overall) than in the albumen (0.5% overall). Egg contamination frequencies were not significantly different between the 3 SE strains. No contaminated eggs contained more than 67 SE cells per ml and most contained fewer than 1 SE cell per ml. The results of this study suggest that refrigeration standards must address the epossibility than SE may sometimes be deposited more frequently in yolk tha in albumen.
Technical Abstract: Because egg yolk and albumen differ substantially in their abilities to support bacterial growth, the initial level and location of Salmonella enteritidis (SE) deposition are critical for determining whether proposed standards for refrigerating eggs are likely to protect public health by preventing extensive microbial multiplication. In the present study, three groups of laying hens were infected with oral doses of approximately 1 billion cells of different SE strains (two were phage type 4 and one was phage type 13a) in two replicate trials. For all three SE strains, the incidence of yolk contamination (approximately 2.5% overall) was significantly greater than the incidence of albumen contamination (approximately 0.5% overall). The phage type 13a strain was less often isolated from fecal samples at 2 weeks post-inoculation than were the phage type 4 strains, but no significant differences between strains were observed in the incidence of egg contamination. Most freshly laid contaminated eggs contained fewer than 1 SE cell per ml of egg yolk or albumen, and no sample contained more than 67 SE cells/ml.