Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/27/2007
Publication Date: 6/1/2008
Citation: Musgrove, M.T., Northcutt, J.K., Jones, D.R., Cox Jr, N.A., Harrison, M.A. 2008. Enterobacteriaceae and Related Organisms Isolated from Shell Eggs Collected During Commercial Processing. Poultry Science. 87:1211-1218.
Interpretive Summary: Little information has been generated about the number of genera and species of bacteria that can be recovered from egg shells. A survey was conducted at three different shell egg processing facilities. In all three plants there were significantly higher proportions of bacterial species recovered from eggshells before eggs were washed (70-83%) compared to after they were washed and packed (5-11%). It was also determined that aquatic genera such as Aeromonas, Vibrio, and Listonella persisted on washed eggs despite a low overall prevalence. Typical spoilage organisms such as Pseudomonas, Sphingobacterium and Chryseomonas were removed. Escherichia and Enterobacter were the most common genera recovered. This information will be used by researchers exploring better means of sanitation and processing efficacy so that retail shell eggs will be delivered to consumers with an even smaller risk of being involved in sporadic or outbreaks of egg-borne disease.
Technical Abstract: In the United States, commercial shell eggs are washed and graded prior to retail. Since passage of the Egg Products Inspection Act in 1971, processing guidelines have been set to ensure that external and internal characteristics are maintained. However, less is known about how commercial processing affects the safety of shell eggs. In order to identify enteric bacteria entering plants and persisting throughout processing, eggs were collected from three U.S. commercial shell egg processing plants on three separate visits. On each plant visit, 12 eggs were collected from each of 12 sites along the processing line: accumulator, pre-wash rinse, 1st washer, 2nd washer, sanitizer rinse, dryer, oiler, check detection/scales, 2 egg grader packer head lanes, re-wash belt entrance, and re-wash belt exit. Each egg was sampled by a rinse technique and rinsate was plated onto violet red bile glucose agar with overlay for the detection and enumeration of Enterobacteriaceae. From each plate, up to five colonies were randomly selected and isolated for identification to genus or species using biochemical tests. Several genera and species were detected at each of the three plants. Sites from which the greatest numbers of isolates were identified were those collected from eggs during pre-processing (accumulator, pre-wash rinse) or eggs judged as dirty (re-wash belt entrance or exit). Sites yielding the smallest number of isolates were those during or at the end of processing. Escherichia coli and Enterobacter spp. were isolated from each of the nine plant visits. Other genera isolated from at least one of the three plants included Cedecea, Citrobacter, Erwinia, Hafnia, Klebsiella, Kluyvera, Leclercia, Morganella, Proteus, Providencia, Rahnella, Salmonella, and Serratia. Non-Enterobacteriaceae isolated and identified included Aeromonas, Chryseomonas, Listonella, Pseudomonas, Sphingobacterium, Vibrio, and Xanthomonas. All of the genera and species were recovered less frequently from fully processed eggs than from unwashed eggs, indicating that shell eggs are less contaminated with bacteria as a result of commercial washing procedures.