More human illnesses caused by Salmonella enterica subspecies enterica serovar Enteritidis throughout the world have been linked to the consumption of contaminated eggs than to any other food vehicle, according to a recent paper in Poultry Science.

Richard K. Gast from the USDA ARS Egg Safety and Quality Research Unit in Athens, Georgia and co-authors there and at North Carolina State University explain that deposition of this pathogen in the edible contents of eggs occurs when systemic infections of laying hens involve colonisation of reproductive organs.

In recent years, the consequences of different housing systems for laying flocks have become the focus of international attention from both animal welfare and public health perspectives. Nevertheless, many questions remain unresolved regarding the food safety implications of various laying hen production systems.

Their study assessed the effects of two different housing types - conventional cages and colony cages enriched with perching, nesting and scratching areas - on the invasion of internal organs by Salmonella Enteritidis in experimentally infected laying hens.

In two trials, groups of laying hens housed in each cage system were orally inoculated with doses of 1.0 × 10⁷ colony-forming units (cfu) of Salmonella Enteritidis. At five to six days post-inoculation, hens were euthanised and samples of internal organs were removed for bacteriologic culturing.

For both trials combined, Salmonella Enteritidis was recovered from 95.3 per cent of caecal samples, with no significant differences observed between housing systems. However, Salmonella Enteritidis was detected at significantly (P<0.05) higher frequencies from hens in conventional cages than from hens in enriched cages for samples of livers (96.9 versus 75.0 per cent), spleens (93.8 versus 53.1 per cent), ovaries (25.0 versus 10.4 per cent) and oviducts (19.8 versus 2.1 per cent).

Gast and co-authors concluded these results demonstrate that differences in housing systems for egg-laying flocks can affect the susceptibility of hens to colonisation of internal organs by Salmonella Enteritidis.

Reference

Gast R.K., R. Guraya, D.R. Jones and K.E. Anderson. 2013. Colonization of internal organs by Salmonella Enteritidis in experimentally infected laying hens housed in conventional or enriched cages. Poult. Sci. 92(2):468-473. doi: 10.3382/ps.2012-02811

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April 2013