Phenotypic and genotypic investigation into the survival of Salmonella Typhimurium and Salmonella Hessarek in eggs at different storage temperatures

Salmonella (S.) Hessarek is an emerging serotype with limited characterisation compared to S. typhimurium. Recent S. Hessarek-related foodborne outbreaks linked to the consumption of egg products have raised concerns about this pathogen. However, little is known about its survival capabilities in egg-related environments or genomic features. This study compared their survival potential under 5 °C, 15 °C, and 25 °C over 28 days, and characterised the genomic features of S. typhimurium and S. Hessarek through whole-genome sequencing. Both strains showed significantly lower bacterial loads in eggshell crushes at 5 °C than at 15 °C or 25 °C, and egg internal contents were Salmonella-positive when contaminated eggs were stored at 15 °C and 25 °C, which may pose a greater risk of contamination at unrefrigerated temperatures. Both strains share core pathways related to genetic information processing, environmental information processing, signalling and cellular processes, and carbohydrate metabolism, supporting their persistence under diverse conditions. However, the absence of some genes in S. Hessarek that are associated with motility and anaerobic metabolism may partially explain its reduced ability to adapt to dry or nutrient-scarce environments on the eggshells, compared to S. typhimurium. Overall, S. typhimurium and S. Hessarek possessed genomic and phenotypic traits that allow them to persist in different egg components under various conditions, though they appeared to show differences in their survivability. Further studies are essential to explore the differences in their survival mechanisms and whether their virulence potential will be influenced by incubating at 15 °C or less in different egg components.