Exposure of Laying Hens to Different Oral Doses of <em>Salmonella enteritidis</em>

Oral exposure dose significantly affected some important parameters of S. enteritidis infection in laying hens and thus could impact testing effort, according to recently published research from the Russell Research Center in the US.

9 July 2011

3 minute read

The effects of exposing laying hens to different oral doses of Salmonella enteritidis were studied by Richard Gast and colleagues at the USDA ARS Egg Safety and Quality Research Unit at the Russell Research Center in Athens, Georgia. Their paper is published in International Journal of Poultry Science.

Contaminated eggs produced by infected laying hens continue to pose a significant public health concern as a leading source of transmission of Salmonella enteritidis infections to humans, according to the Athens researchers. A recently implemented national regulatory programme for egg-producing poultry in the United States seeks to control eggborne transmission of illness to consumers via a diverse program of mandatory risk reduction practices plus testing to detect infected flocks.

However, they explain, many aspects of S. enteritidis infections in laying hens, including the precise relationship between the magnitude of oral exposure and infection parameters such as the numbers of bacteria that reach internal tissues, remain unresolved.

In the present study, groups of laying hens were experimentally infected with oral doses of 10⁴, 10⁶, or 10⁸ CFU of a phage type 13a strain of S. enteritidis and the number of S. enteritidis cells in the livers of infected hens was determined at five and 20 days post-inoculation.

The frequency of S. enteritidis recovery from livers ranged from 30 per cent (10⁴ CFU dose) to 90 per cent (10⁸ CFU dose) at five days post-inoculation and from 0 per cent (10⁴ CFU dose) to 40 per cent (10⁸ CFU dose) at 20 days post-inoculation.

Significantly (p<0.05) greater numbers of S. enteritidis were isolated from livers at both five and 20 days post-inoculation following inoculation with 10⁸ CFU than after administration of either of the two lower doses.

These results demonstrate that the oral exposure dose significantly affects important parameters of S. enteritidis infection in laying hens and could thereby influence the outcome of testing efforts.

Interpreting the potential implications of testing results and improving the effectiveness of testing protocols are both contingent on understanding how different levels of exposure are likely to be detected by particular sampling methods.

Reference

Gast R.K., R. Guraya, J. Guard and P.S. Holt. 2011. Exposure of laying hens to different oral doses of Salmonella enteritidis. International Journal of Poultry Science, 10 (4): 325-331.