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United States Department of Agriculture

Agricultural Research Service

Title: Identification of Enterobacteriaceae from Washed and Unwashed Commercial Shell Eggs

Authors
item Musgrove, Michael
item Jones, Deana
item Northcutt, Julie
item Cox, Nelson
item Harrison, Mark - UGA

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 19, 2004
Publication Date: November 1, 2004
Citation: Musgrove, M.T., Jones, D.R., Northcutt, J.K., Cox Jr, N.A., Harrison, M. 2004. Identification of enterobacteriaceae from washed and unwashed commercial shell eggs. Journal of Food Protection. 67:2613-2616.

Interpretive Summary: Information on how shell eggs processed by commercial plants are affected by storage has not been available. Eggs collected from a commercial facility which were washed were compared to those which were not washed. Levels of contamination by Enterobacteriaceae were determined using selective media. Isolates from agar plates were randomly selected, streaked for isolation, and identified to genus or species using biochemical tests. Bacteria were recovered more often and in greater numbers from unwashed than from washed egg shells. Commercial washing removed many pathogens from egg shells including Salmonella, Serratia, Klebsiella pneumoniae, and Enterobacter sakazakii. This information can be used by regulatory agencies when formulating HACCP regulations for the industry. It will also be useful to the egg industry as they compose SSOPS and HACCP plans.

Technical Abstract: In order to evaluate the effect of processing on the safety and quality of retail shell eggs, a storage study was conducted with unwashed and commercially washed eggs. For each of three replications, shell eggs were purchased from a retail processing plant, transported back to the laboratory, and stored at 4 oC. Once a week for six weeks, twelve eggs for each treatment (washed and unwashed control) were rinsed in phosphate buffered saline. In addition, three composite samples consisting of the contents of three eggs were also collected. A 1 ml aliquot of each sample was then plated onto violet red bile glucose agar with overlay and incubated at 37 C for 24 h. Following incubation, plates were observed for colonies characteristic of the family Enterobacteriaceae. A maximum of ten isolates per positive sample were streaked for isolation before being identified to the genus or species level using commercially available biochemical strips. Although most of the isolates from the unwashed control eggs belonged to the genera Escherichia or Enterobacter, many other genera and species were identified. These included Citrobacter, Klebsiella, Kluyvera, Pantoea, Providencia, Rahnella, Salmonella, Serratia, and Yersinia. Non-Enterobacteriaceae also recovered from the egg samples included Aeromonas, Xanthomonas and Flavimonas. There were very few washed egg samples that were found to be contaminated with these bacteria. These data provide useful information on the effectiveness of processing in improving the microbiology of commercial shell eggs.

Last Modified: 4/24/2014
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