Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 18, 2004
Publication Date: November 1, 2004
Citation: Musgrove, M.T., Jones, D.R., Northcutt, J.K., Harrison, M.A., Cox Jr, N.A. 2004. Identification of enterobacteriaceae and related organisms from rinses of eggs collected during processing in commercial shell egg processing plants in the southeastern united states. Journal of Food Protection, Vol. 67. No. 11, 2004: 2613-2616 Interpretive Summary: Little published information is available on how commercial processes affect species of Enterobacteriaceae on the shells of eggs. Eggs were collected from commercial plants at different points along the processing chain and their shells were analyzed for the presence of Enterobacteriaceae. This is a group of organisms that includes Escherichia coli and Salmonella. Isolates were obtained from the microbial analyses and were identified to the genus or species level using biochemical testing. This allowed us to determine which species were most common on unwashed eggs. It also showed us which species were most likely to be found at the end of the commercial process. Twenty-two species of bacteria were found by these methods. Escherichia coli and Enterobacter spp. were most common. All Salmonella spp. were removed but Vibrio and Aeromonas were occasionally detected on processed eggs. Regulatory agencies and industry will use this information when considering HACCP regulations and plans. This data serves as a validation of the current commercial process while demonstrating potentials for it's improvement that will allow for an increase in the microbiological safety and quality of shell eggs.
Technical Abstract: In the United States, shell eggs are washed and graded prior to retail. Since passage of the Egg Inspection Act in 1970, processing guidelines have been set to ensure that external and internal characteristics are improved. However, less is known about safety of commercially processed shell eggs. In order to determine genus or species of 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 positive plate, up to five colonies were randomly selected and isolated for further analysis. Using biochemical tests, isolates were identified to the genus or species level. 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. As all of the genera and species were recovered less frequently from fully processed eggs than from unwashed or in process eggs, these data indicate that shell eggs from the Southeastern United States are less contaminated with bacteria of fecal origin as a result of commercial washing procedures currently being used. Key Words: shell eggs, Enterobacteriaceae, commercial processing