ARS | Publication request: Detecting Salmonella Enteritidis in Laying Hens and Eggs after Experimental Infection at Different Oral Dose Levels

Submitted to: International Association for Food Protection
Publication Type: Abstract Only
Publication Acceptance Date: March 15, 2012
Publication Date: July 15, 2012
Citation: Gast, R.K., Guraya, R., Guard, J.Y., Holt, P.S. 2012. Detecting Salmonella Enteritidis in Laying Hens and Eggs after Experimental Infection at Different Oral Dose Levels. International Association for Food Protection. 74(SupplementA):52.

Technical Abstract: The attribution of human illness to eggs contaminated with Salmonella Enteritidis has led to substantial commitments of resources (by both government and industry) to risk reduction and testing programs in egg-laying flocks. Cost-effective application of testing requires a thorough understanding of the outcomes of S. Enteritidis infections in hens. This study sought to resolve incompletely understood aspects of S. Enteritidis infections in laying hens which affect flock testing efforts, including relationships between quantitative oral exposure levels and important detectable parameters: the frequency and duration of fecal shedding, the frequency and magnitude of internal organ colonization, and the frequency of deposition inside developing eggs. In six trials, groups of specific-pathogen-free laying hens were experimentally infected with oral doses of 104, 106, or 108 CFU of phage type 13a S. Enteritidis. Fecal shedding was monitored for 8 wk post-inoculation (PI), the frequency and concentration of S. Enteritidis cells in livers were determined at 1 and 3 wk PI, and eggs were collected for 4 wk PI and cultured for S. Enteritidis contamination in yolk and albumen. Fecal shedding of S. Enteritidis declined over time and was last detected in the 104 CFU dose group at 3 wk PI. At 4 wk PI, 6% of hens in the 106 cfu dose group and 28% of hens in the 108 CFU dose group shed S. Enteritidis in feces; a few birds in these groups were still shedding at 8 wk. S. Enteritidis was isolated from 65% of livers from hens given 108 CFU but from only 15% of hens given 104 CFU, and the highest inoculation level was likewise associated with significantly (P < 0.05) higher S. Enteritidis concentrations in livers. Increasing inoculation doses were associated with both significantly more frequent egg contamination and a significantly higher propensity toward deposition in albumen. These results demonstrate that the oral exposure dose has significant effects on important detectable parameters of S. Enteritidis infection in laying hens which could potentially influence testing outcomes.