Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/1996
Publication Date: N/A
Interpretive Summary: Salmonella enteritidis (SE) contamination of eggs has become a significant source of human illness in recent years. Bacteriological culturing to detect SE in eggs is an important aspect of programs to reduce the likelihood that contaminated eggs will reach consumers, but egg culturing is slow and labor-intensive. Flocks are thus generally subjected to preliminary screening tests, which should ideally be able to detect infection with high sensitivity and to consistently predict the probability of egg contamination. In the present study, hens were experimentally infected with SE and eggs were collected and cultured for SE in the contents. Eggs from each hen were also tested for the presence of specific yolk antibodies using two enzyme immunoassay methods. Samples of voided feces were also collected from each bird and cultured for SE. Although the shedding of SE in feces decreased over time while egg yolk antibodies were more easily found in the later stages of the experiment, both of these types of tests were determined to be useful for predicting whether particular hens would lay contaminated eggs. Over 80% of the hens that laid SE-contaminated eggs were detected as infected by fecal culturing and over 90% by one of the assays for egg yolk antibodies. Egg yolk antibody testing allows rapid and effective screening to identify SE- infected laying flocks using easily collected samples.
Technical Abstract: Detecting Salmonella enteritidis (SE) contamination in eggs is the focus of many programs for reducing egg-borne disease transmission, but egg culturing is time-consuming and laborious. Screening tests are thus generally applied to reduce the number of flocks from which eggs are cultured. The usefulness of such tests is directly proportional to their detection sensitivity and to their ability to predict the likelihood of egg contamination. In the present study, samples were collected for 24 days after laying hens were orally inoculated with SE. Eggs from each hen were cultured for SE in the contents and samples of egg yolk were diluted and tested for specific antibodies to SE flagella using experimental and commercially available ELISA methods. Samples of voided feces were collected regularly from each bird and cultured for SE. Although fecal shedding and egg yolk antibody production followed opposite patterns over time (fecal shedding decreased as egg yolk antibody titers increased), tests for both parameters effectively predicted whether particular hens would lay contaminated eggs. Among hens that laid at least one egg contaminated by SE, 82% were detected as infected by fecal culturing and 96% by the experimental egg yolk ELISA test. Egg yolk antibody testing involves easy sample collection and allows rapid and effective screening to identify SE-infected laying flocks that might lay contaminated eggs.