Salmonella enteritidis colonization of the reproductive tract and forming and freshly laid eggs of chickens

Salmonella enteritidis colonizes the tissues of the chicken ovary and oviduct, presumably contaminating eggs and thereby contributing to human outbreaks of salmonellosis. In this study, commercial adult laying hens were given an oral inoculation of 10(8) S. enteritidis organisms. Tissues from various organs, the intestines, and the reproductive tract, including freshly laid eggs, were collected daily for up to 40 days postinoculation (p.i.). Within 2 days p.i. S. enteritidis was detected by culture in pools of the spleen, liver, heart, and gallbladder tissues, in intestinal tissues of all infected birds, and in various sections of the ovary and oviduct. Detection of organisms by immunohistochemical staining was rare for most tissues in spite of their culture-positive status, suggesting a low level of tissue colonization. However, S. enteritidis could be detected by immunohistochemical staining in oviduct tissues associated with four forming eggs, indicating the possibility of a heavier colonization in the egg during its development. In two subsequent experiments, forming eggs taken from the oviduct with their associated tissue, were found to be culture positive for S. enteritidis at a rate of 27.1 and 31.4%, while freshly laid eggs in these experiments were culture positive at the rate of 0 and 0.6%. These observations suggest that while forming eggs are significantly colonized in the reproductive tract, factors within the eggs may control the pathogen before the eggs are laid. The data show that prior to egg deposition, forming eggs are subject to descending infections from colonized ovarian tissue, ascending infections from colonized vaginal and cloacal tissues, and lateral infections from colonized upper oviduct tissues. The data are consistent with an ascending infection of freshly laid eggs from the cloaca, as the incidence of positive eggs in experiments 1 and 3 coincided with heavily contaminated cloacal tissues (50.7 and 80%, respectively), while no positive eggs were detected in experiment 2 when cloacal colonization was low (8.3%). The data do not support the possibility of egg invasion by bacterial translocation from the peritoneal cavity.