Metabolomic Analysis of Electron Beam Inactivated Salmonella Typhimurium

Introduction: Outbreaks of Salmonella Typhimurium continue to be a leading cause of foodborne illness worldwide. Although food safety interventions, such as ionizing radiation, are implemented and are highly effective in inactivating pathogens such as Salmonella, these pathogens can remain metabolically active.

Purpose: Understanding how the metabolomic activity of irradiated cells changes over time can help the food industry better exploit these metabolically active yet nonculturable (MAyNC) cells for their immune modulating capabilities.

Methods: A 10⁹ CFU/ml titer of Salmonella Typhimurium (ATCC 13311) was suspended in phosphate buffered saline and irradiated at a lethal target dose of two kGy. Culture methods were used to confirm the nonculturable state of the irradiated cells. Untargeted metabolomic analysis was performed on unirradiated cells, freshly irradiated cells, and irradiated cells that were incubated at room temperature for 24 hours.

Results: Three hundred forty-nine metabolites were identified using untargeted metabolomic analysis. Eighty-eight of these were expressed at statistically different concentrations (P<0.01) between the treatment groups. Pathways that were impacted (P<0.01) include Glyoxylate/Dicarboxylate metabolism, Arginine/Proline metabolism, Glycine/Serine/Threonine metabolism, beta-Alanine metabolism, Alanine/Aspartate/Glutamate metabolism, and Inositol phosphate metabolism.

Significance: These results show that the metabolomic profile of irradiated Salmonella Typhimurium greatly differs between unirradiated cells, freshly irradiated, and irradiated cells that were incubated for 24 hours. The pathways elicited suggest that not only does ionizing radiation have an effect on the metabolites being produced within the cell, but this stress continues to cause changes even after 24 hours at room temperature. The immune modulating properties of these inactivated pathogens in food is worthy of investigation.