Submitted to: Poultry Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/13/2001
Publication Date: 7/3/2001
Citation: Gast, R.K., Holt, P.S. 2001. Assessing the frequency and consequences of salmonella enteritidis deposition on the egg yolk membrane. Poultry Science. Interpretive Summary: The contamination of eggs with Salmonella enteritidis (SE) is an important source of human illness. Refrigeration hopes to prevent small numbers of SE from multiplying to more dangerous levels, but SE inside yolks might continue to grow during early stages of egg cooling. This study determined whether SE placed onto the exterior membrane surface of egg yolks was able to penetrate into and multiply within the interior yolk contents. When small numbers of SE were inoculated onto the yolk membrane surface, a significant degree of penetration and multiplication within the yolk contents was observed in about 75% of samples after 24 hours at 25 C but in only 20% of samples incubated for 72 hours at 15 C. Another part of this study determined whether SE was more often associated with the yolk membrane or found inside the yolk contents of eggs laid by experimentally infected hens. SE was found in about 4% of samples that included the yolk membrane, but in only 0.5% of samples containing only yolk contents. Although deposition of SE within egg yolks does not appear to occur frequently, rapid refrigeration of eggs is still important to prevent the penetration of SE into and multiplication within egg yolks.
Technical Abstract: The first part of this study determined whether SE inoculated onto the exterior (vitelline) membrane surface of egg yolks was able to penetrate into and multiply within the yolk contents. When 100 cfu of SE was inoculated onto the exterior surface of intact egg yolks, multiplication within the interior yolk contents occurred in 10% of samples after 6 hours of incubation and in 75% of samples after 24 hours at 25 C (reaching mean levels of about 10,000 cfu/mL), but in only 20% of samples incubated for 72 hours at 15 C. The second part of this study applied an oral infection model in laying hens to establish the relative proportions of contaminated eggs in which SE deposition was associated with the yolk membrane or was found inside the yolk contents. Although approximately 4.3% of eggs yolks were positive for SE when both yolk contents and membranes were sampled, only about 0.5% of samples of yolk contents (without membranes) were positive. Although deposition of SE within egg yolks appears to occur infrequently, rapid refrigeration of eggs is necessary to prevent the penetration of SE into and multiplication within egg yolks.