Skip to main content
ARS Home » Research » Publications at this Location » Publication #180036


item Musgrove, Michael
item Jones, Deana

Submitted to: Feedinfo News Service
Publication Type: Trade Journal
Publication Acceptance Date: 4/25/2005
Publication Date: 4/26/2005
Citation: Musgrove, M.T., Jones, D.R. 2005. Identification of enterobacteriaceae from washed and unwashed commercial shell eggs. Feed Information for News on the Web. Available:

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: 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. This work demonstrated that commercial processing decreased microbial contamination of eggshells. In order to know which species persisted during storage on washed or unwashed eggs, Enterobacteriaceae isolates were selected and identified biochemically. For each of three replications, shell eggs were purchased from a commercial 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 sterile phosphate buffered saline. A 1 ml aliquot of each sample was plated onto violet red bile glucose agar with overlay and incubated at 37 oC 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 unwashed egg samples included Xanthomonas and Flavimonas. There were very few washed egg samples that were found to be contaminated with any of these bacteria. These data provide useful information on the effectiveness of processing in removing microorganisms from commercial shell eggs.