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Listen to this siteWednesday 25 June 2003
This research project will investigate the growth of salmonella in eggs.
Study Duration : August 2001 to April 2003
Contractor : Public Health Laboratory Service
It is generally assumed that even at ambient temperatures (20°C to 25°C) the growth of Salmonella enteritidis in eggs will be minimal over a period of 3 to 4 weeks. After this time there is the possibility of very rapid growth as the internal defence mechanisms of the eggs are broken down. This delay in rapid growth is the basis of many of the current food management options for minimising the likelihood of contracting salmonellosis from eggs.
Although most research tends to support this delay of growth, there is some evidence to suggest that such a delay may not occur with all eggs. In experiments using eggs artificially contaminated with S. enteritidis , rapid growth after only a few days has been observed in a small proportion of the eggs. Research was required to investigate whether this rapid growth is ‘real’ (i.e. it occurs in naturally contaminated eggs) or is an artefact of the methodology used to artificially contaminate eggs.
A principal objective of the proposed study is to try and correlate the growth of salmonella in egg contents with critical elements of egg chemistry and biochemistry. To this end, a range of measurements will be undertaken on egg contents, principally on egg albumen, including: measurement of iron, ovotransferrin and glucose in albumen, pH, albumen quality and yolk size.
Additionally, the study will investigate defined, isogenic and naturally occurring mutants of S. enteritidis and S. typhimurium to determine the bacterial factors important in the growth survival of salmonella in egg contents. The effects of bird age in commercial caged layer flocks on the ability of shell eggs to support/control the growth of salmonella will also be examined.
The aim of this study was to identify the factors that allow Salmonella enteritidis to survive and multiply within the egg and to compare these to other strains of salmonella.
High levels of glucose, and a low capacity of the iron-binding proteins in the albumen were factors that were found to be linked to high levels of bacterial growth.
Salmonella enteritidis was found to have a number of abilities that allow growth to a high level. It was able to survive well in the albumen at hen body temperature and it could use the glucose present in fresh eggs as an energy source. The combination of certain surface structures and the ability to survive in the albumen shown by S. enteritidis is not shared by other salmonella strains that have been widespread in the past, such as S. gallinarum , S. pullorum and S. typhimurium .
The final report is available from the FSA Library and Information centre.
To obtain a copy, please contact the Enquiry Desk, Dr John Dixon, Library and Information Services, Food Standards Agency (020 7276 8181/8182 or at library&info@foodstandards.gsi.gov.uk ).
Contact
: For any enquiries concerning this research project, please contact the relevant programme contact or email
science@foodstandards.gsi.gov.uk
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