Submitted to: Avian Diseases
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/25/2005
Publication Date: 9/1/2005
Citation: Gast, R.K., Bouldin, J.G., Holt, P.S. 2005. The relationship between the duration of fecal shedding and the production of contaminated eggs by laying hens infected with strains of salmonella enteritidis and salmonella heidelberg. Avian Diseases. Vol 49:382-386. Interpretive Summary: Public health authorities have been concerned for nearly twenty years that eggs containing Salmonella enteritidis in their edible liquid contents can transmit disease to humans. More recently, the Centers for Disease Control and Prevention has also reported a link between eggs and S. heidelberg infections in humans. Very substantial resources have been invested in programs to detect and control S. enteritidis infections in commercial egg-laying flocks. Although the first step in the establishment of Salmonella infections of poultry is the colonization of the intestinal tract, the relationship between the duration of this colonization and the likelihood that hens will lay contaminated eggs has not been certain. In the present study, groups of laying hens were infected by oral inoculation with large doses of S. enteritidis and S. heidelberg strains. Some of these (the "parent" strains) had been given to hens in a previous study and re-isolated from eggs laid by the infected birds to yield the "passaged" strains. Feces from all infected hens were tested for Salmonella for six weeks and eggs laid by the hens between the 5th and 22nd days after inoculation were also tested. The previously passaged Salmonella strains were found in feces for longer than were the original parent strains and the passaged strains caused more contaminated eggs to be produced than did the parent strains. However, the persistence of the S. enteritidis and S. heidelberg strains in the intestinal tract did not correlate with the frequencies at which they caused egg contamination.
Technical Abstract: Egg contamination by Salmonella enteritidis has remained a significant public health problem for nearly two decades and S. heidelberg has also been recently implicated in egg-transmitted human illness. Colonization of the intestinal tract is a necessary precursor to the invasion of reproductive organs and subsequent deposition inside eggs laid by infected hens, but the relationship between the persistence of Salmonella in the intestinal tract and the likelihood of egg contamination has been uncertain. In the present study, groups of laying hens were inoculated with large oral doses of strains of S. enteritidis and S. heidelberg, including variants of the original parent strains that had been re-isolated from eggs laid by infected hens in a prior study. The shedding of Salmonella in voided feces was monitored for six weeks postinoculation and all eggs laid by infected hens between five and 22 days postinoculation were cultured for Salmonella in their contents. The mean duration of fecal shedding was significantly longer for the previously passaged Salmonella strains (26.7 days) than for the original parent strains (17.5 days), and the passaged strains caused a significantly higher frequency of egg contamination (6.4%) than did the parent strains (3.3%). However, intestinal persistence and egg contamination were not correlated for any of the S. enteritidis or S. heidelberg strains.