Experimental infection of egg-laying hens with Salmonella enteritidis phage type 4

Chickens were inoculated intravenously with 10(5) or 10(6) organisms. Heavy infection of the ovaries occurred and some infection persisted in this organ for several weeks. Most of the ovarian infections were confined to the interstitial tissues and not to the yolk contained in the large follicles. Infections of the ovary did not result from contamination from infected air sacs. None of 810 eggs laid contained S. enteritidis. Chickens infected orally gave similar results to those following intravenous inoculation although the number of isolations obtained from the caeca and cloaca were higher. S. enteritidis was isolated from two of 633 eggs in which the contents only were cultured and from 36 of 614 eggs in which both shell and contents were cultured. The serum IgG response to oral inoculation was monitored by an ELISA using a whole cell sonicate or lipopolysaccharide antigen. High titres of IgG were detected for 27 weeks after infection when the experiment was terminated. The experiments suggest that most infected eggs laid by 5. enteritidis-infected hens are surface-contaminated and do not result from infected ovaries.