Ensuring egg safety: Salmonella survival, control, and virulence in the supply chain

Salmonella contamination of eggs is a global food safety concern, producers, regulatory authorities, and affecting public health. To mitigate Salmonella risks on-farm and along the supply chain, egg producers have adopted various quality assurance, animal husbandry, and biosecurity practices recommended by organizations such as Australian eggs, the European Commission, and the US Department of Agriculture (USDA). However, egg storage requirements vary significantly worldwide. In Australia, most states follow the Food Standards Australia New Zealand, but discrepancies exist. In the United States, the USDA mandates refrigeration of eggs below 7.2°C to prevent Salmonella growth, whereas the European Union requires that eggs must not be refrigerated to avoid condensation, which may promote bacterial growth. Refrigeration of eggs is associated with reduced Salmonella growth and decreased infection risk. Yet, conflicting data regarding the impact of storage temperatures on Salmonella survival may contribute to the disparity between international recommendations for egg storage. Studies indicated better Salmonella survival in egg contents at 5°C due to higher expression levels of survival and stress response-related genes compared to 25°C, yet this may not lead to an increased risk or higher severity of Salmonella infection. Evidence suggests that storing eggs at less than 7°C will influence the virulence of bacteria. Warmer storage temperatures may lead to increased potential of Salmonella multiplication in the nutrient-rich yolk and may cause the expression of certain virulence genes. Eggs can be exposed to various temperatures in the supply chain. Further studies are essential to understand the relationship between the storage temperature on the farm, in the supply chain, and bacterial virulence.