The repair mechanism of sublethal Salmonella by intense pulsed light treatment

Recently, intense pulsed light (IPL) technology, as a novel non-thermal sterilization method, has been increasingly applied to the inactivation of microorganisms, such as Salmonella, in food processing industry. Simultaneously, an emerging concern arises from the sublethal injuries of microorganisms caused by these non-thermal sterilization techniques. In this study, IPL (0.98 J/cm2/pulse luminous flux) showed different bactericidal capacity for Salmonella in water, LB broth, and on the surface of chicken, respectively reducing by approximately 5, 2.11 and 1.77 log CFU/mL after one application performed at a 3 cm distance. These differences were attributed to the induction of sublethal injury in Salmonella by IPL treatment, which can subsequently be repaired within nutrient-rich environments, such as foods or broths. To elucidate the repair mechanism, several intracellular oxidative damage enzymes were measured in sublethal Salmonella with IPL treatment, and then the differentially expressed genes of the sublethal cells were examined by RNA-seq. In the results, the levels of TrxR, NOX, and endogenous H2S were significantly increased (27, 2 and 5 fold, respectively); and 264 of 793 identified differentially expressed genes were functionally associated with responding to the IPL stimulus, which were enriched in DNA replication, DNA repair, cell membrane protein, oxidative response, amino acid synthesis and metabolism, and ABC transporters. Therefore, the study identified two key repair mechanisms: repairing membrane proteins and addressing DNA damage. In conclusion, the repair mechanism of Salmonella under IPL stimulus explored in this study provides a new idea for reducing and controlling pathogenic bacteria in the food industry.