Effect of Storage Temperatures on the Survival of Salmonella and Campylobacter in Chicken Eggs

Introduction: Human infections with Salmonella and Campylobacter are mainly from consumption of raw or undercooked eggs and poultry.  Foodborne illness caused by Salmonella is a worldwide problem. Salmonella contaminated eggs present a hazard for consumers during handling; contaminated eggs can contaminate other surfaces during food preparation.  Campylobacter strains were used in this study, even though there is disagreement among scientists regarding egg passage of Campylobacter to poultry through eggs.

Purpose: The objective of this study was to evaluate the survival of inoculated Salmonella and Campylobacter on egg shells and egg contents.

Methods: The initial Salmonella and Campylobacter egg inoculation levels were 2 log CFU/egg and 4 log CFU/egg for both external and internal contamination. Salmonella and Campylobacter inoculated eggs were subjected to different storage temperatures: 30°C and 23°C for 0, 6, 24, 48 hours and 4°C for 1, 7, 14, and 21 days.  Confirmation of Salmonella and Campylobacter isolated from eggs were subjected to Polymerase Chain Reaction.

Results: Generally, there was a decline on the levels of Salmonella on shell eggs. Recovery of Salmonella at 4°C for 1, 7, 14, and 21 days  from internal contamination was between 4.76 -2.56 CFU/ml. Salmonella population increased (6.00– 7.51 CFU/ml ) in internal contaminated eggs at 30°C and 23°C. No viable Campylobacter cells were indicted on shell eggs stored at 4°C, even after the enrichment. For internal contamination, Campylobacter populations decreased (3.24 – 2.32 CFU/ml) for eggs stored at 4°C for 6 hr and 1 day. At day 14, the bacterium was not detected even after enrichment.

Significance: The present study demonstrates Salmonella in eggs can multiply at room temperature and unrefrigerated conditions. Campylobacter can survive inside the egg contents for up to 14 days after internal contamination.  Results of this study reinforce the critical importance of egg refrigeration in order to protect consumers from Salmonella and Campylobacter infections.