Enterobacteriaceae and Related Organisms Isolated from Shell Eggs Collected During Commercial Processing

In the United States, commercial shell eggs are washed and graded before 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. To identify enteric bacteria entering plants and persisting throughout processing, eggs were collected from 3 US commercial shell egg-processing plants on 3 separate visits. On each plant visit, 12 eggs were collected from each of 12 sites along the processing line: accumulator, prewash rinse, first washer, second washer, sanitizer rinse, dryer, oiler, check detection/scales, 2 egg grader/packer head lanes, rewash belt entrance, and rewash belt exit. Each egg was sampled by a rinse technique, and the rinsate was plated onto violet red bile glucose agar with overlay for the detection and enumeration of Enterobacteriaceae. From each plate, up to 5 colonies were randomly selected and isolated for identification to genus or species by using biochemical tests. Several genera and species were detected at each of the 3 plants. Sites from which the greatest numbers of isolates were identified were those collected from eggs during preprocessing (accumulator, prewash rinse) or from eggs judged as dirty (rewash 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 9 plant visits. Other genera isolated from at least 1 of the 3 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.