Experimental oral infection of specific pathogen-free laying hens and cocks with Salmonella enteritidis strains

A total of 105 specific pathogen-free (SPF) laying hens and eight cocks were orally infected with strains of Salmonella enteritidis. The organs of these animals were examined bacteriologically for up to 6 weeks post infectionem (p.i.). One-half of the eggs laid on a single day were examined 1 day after laying, and the other half 28 days after laying. The siderophore, ferrioxamine E, was added to the pre-enrichment medium. A high correlation was found to exist between colonization of the caecum by salmonellas and the level of contamination of the egg shell. No correlation was found between the contamination of the egg shell and that of the egg content. The strains used for infection were not recovered from any yolk out of a total of 938 eggs. S. enteritidis was isolated from the albumen in four cases (0.4%). Storage of the eggs for 28 days after laying resulted in a decrease in the frequency of salmonella detection on the egg shell and in the egg content. The strains used for infection could be isolated from various sections of the sexual organs for up to 2 weeks p.i. S. enteritidis was most frequently found in the ovary and rarely in the oviduct, but never in the pre-ovulatory mature follicles. In the groups that included salmonella-infected cocks, the salmonella detection frequency did not increase either for the egg content or for the organs of the laying hens. It seems that primary vertical transmission of salmonellas occurs, in rare cases, as a result of an infection of the albumen but not of the yolk.