Pathogen prevalence and microbial levels associated with restricted shell eggs

Authors: Jones, Deana; Musgrove, Michael

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/4/2007
Publication Date: 9/1/2007
Citation: Jones, D.R., Musgrove, M.T. 2007. Pathogen prevalence and microbial levels associated with restricted shell eggs. Journal of Food Protection.70(9):2004-2007

Interpretive Summary: Shell eggs which do not meet quality standards to be sold to consumers are referred to as “restricted eggs”. Restricted eggs which are still considered edible according to USDA standards, may be utilized in further processed egg products. These eggs are washed at the shell egg processing facility and then again before entering the breaking line. Current US egg pasteurization standards were developed in 1971 and are based on the reduction of Salmonella. A study was undertaken to determine the prevalence of common pathogenic bacteria on and within restricted eggs being sent to further processing. Approximately 4.35 log cfu/mL aerobic bacteria were associated with the shells and 1.99 log cfu/mL were found in the egg contents. Enterobacteriaceae (family of bacteria including many common pathogens) levels associated with the shells were 2.35 log cfu/mL. Very low levels of Enterobacteriaceae were found in the contents, but 36.7% of these samples were positive for growth. Only 0.5% of the total shell and contents samples was positive for Campylobacter. Approximately 3% of the total samples were positive for Salmonella, specifically, S. Heidelberg. Consequently, 21% of the total samples were positive for Listeria. Current pasteurization standards should be reconsidered for additional organisms beyond Salmonella. Furthermore, new egg pasteurization methods and technologies should be developed considering a broader range of food pathogens.

Technical Abstract: Restricted shell eggs not meeting quality standards for retail but maintaining acceptable quality for inclusion in further processed eggs are often diverted to further processing. A study was conducted to determine the biological load present on and in these eggs. Restricted eggs were collected from 3 shell egg processing plants in one day. This process was repeated 3 times (replicates). Six shells or egg contents were combined to create a pool. Ten pools of each shells and contents were formed for each plant per replicate. Total aerobic bacteria and Enterobacteriaceae were enumerated. The prevalence of Salmonella, Campylobacter and Listeria were determined by cultural methods. Average aerobic counts associated with the shells were 4.35 log CFU/ml. The contents contained 1.99 log CFU/ml on average. There were plant*replicate differences for both (P < 0.05 and P < 0.01, respectively). The average Enterobacteriaceae level associated with the shell was 2.35 log CFU/ml. Very low levels of Enterobacteriaceae were detected in the egg contents with 36.7 % of samples being positive. One shell sample (0.5 % of total samples) was Campylobacter positive. Two shell samples (1.1 % of total samples) were Salmonella positive. Twenty-one percent of samples were positive for Listeria (33 – shells; 5 – contents). While current pasteurization guidelines are based on Salmonella lethality, the results of this study indicate a need to revisit the guidelines to determine effectiveness for other pathogenic species. Furthermore, a combination of pathogens should be considered as new pasteurization technologies and methods are developed.