Salmonella Contamination in Shell Eggs Exposed to Modified Pressure Imaging for Microcrack Detection

Authors: Jones, Deana; Lawrence, Kurt; Yoon, Seung-Chul; Heitschmidt, Gerald - Jerry

Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/2011
Publication Date: 7/1/2011
Citation: Jones, D.R., Lawrence, K.C., Yoon, S.C., Heitschmidt, G.W. 2011. Salmonella contamination in shell eggs exposed to modified pressure imaging for microcrack detection. Poultry Science. 90:1616-1619.

Interpretive Summary: Cracks in the egg shell, even minute microcracks, present a significant food safety risk to consumers. The shell is one of the first lines of defense for the egg from external microbial contamination. Finding microcracks in the shells of eggs is a difficult task, even for professionally-trained human egg graders. Technology has been developed by a team of USDA ARS scientists in Athens, GA. The technology provides 99.6 % accuracy in detecting cracked eggs. A study was conducted to determine if eggs exposed to the crack detection system would have a higher level of Salmonella contamination in the egg contents and whether microbial cross-contamination would occur within the system. One third of the eggs utilized in the study were externally inoculated with Salmonella Typhimurium and the remaining eggs were dipped in a sterile solution. During each replicate of the study, three sets of eggs from each treatment were assessed in the microcrack detection system in the following order: controls; Salmonella inoculated; post-inoculated controls. No Salmonella Typhimurium was detected in any of the control eggs. The inoculated eggs had 4.79 log cfu/mL of Salmonella Typhimurium present within the shell and corresponding matrix. There was no cross-contamination within the system between inoculated and control eggs. The modified pressure microcrack detection system is safe method to assess eggs for cracks, thus increasing the food safety of US egg supply.

Technical Abstract: Microcracks in eggshells are a food safety risk and are difficult for professional human graders to detect. Modified pressure imaging technology with 99.6 % accuracy has been developed to detect microcracks. This study was conducted to determine whether the microcrack detection system would increase penetration of Salmonella into egg contents or lead to cross contamination within the system. Thirty dozen Grade A large white retail eggs were used for each of three replicates. Cracked eggs were removed and 72 eggs per replicate were dip inoculated in buffered peptone water containing 105 cfu/mL nalidixic acid resistant Salmonella Typhimurium (ST), while 144 eggs were dipped in sterile buffered peptone water. All eggs were incubated overnight at 37 °C before imaging. Forty-five eggs of each treatment were imaged in the following order: control, inoculated, control. Imaged and non-imaged eggs from each treatment were utilized for cultural analysis of a shell rinse, shell emulsion and contents sample for each egg. ST levels were monitored on brilliant green sulfa agar with 200 ppm nalidixic acid. Egg contents were also enriched to determine the prevalence of ST in low levels. ST was not detected on or in any of the control eggs, including the ones imaged after the inoculated eggs. The highest level of ST was detected in inoculated shell emulsions (4.79 log cfu/mL). No differences in ST levels were found for any sample location between imaged and non-imaged inoculated eggs. Therefore, the modified pressure imaging system for microcrack detection did not result in microbial cross contamination or increase the level of microbial penetration in inoculated eggs. The imaging system can be utilized to assess eggs for cracks without negative food safety implications.