Inactivation Mechanism of Low-Energy X-Ray on Salmonella

The problem of food safety and public health caused by bacterial infection has always been a hot issue of social concern, so it is of great significance and application value to explore a safe and efficient food sterilization technology. X-ray irradiation, a new non-thermal sterilization technology with high penetrability that is safety controllable, has a high linear energy transfer (LET) value and relative biological effect (BRE). However, the mechanism for its inactivation effect on foodborne pathogenic bacteria such as Gram-negative bacteria is rarely reported, which greatly limits its application and development in the field of food microbial safety. In this study, the inactivation effect and mechanism of low-energy X-ray on Salmonella, a common foodborne Gram-negative pathogen, were investigated by transcriptomics in an effort to provide a theoretical basis for the application of low-energy X-ray in food safety control. The influence of X-ray irradiation at doses of 0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 kGy on the survival and sublethal effect of Salmonella was analyzed using plate counting method, the effect of X-ray irradiation on bacterial ultrastructure using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) was examined, and the mechanism of Salmonella inactivation by low-energy X-ray was elucidated by transcriptomic analysis. Results showed that the sub-lethal rate of Salmonella was the highest (99.44%) when exposed to 0.5 kGy of X-rays. Low energy X-ray destroyed the bacterial cell wall and membrane. The transcriptome sequencing results showed that among the 292 differentially expressed genes (DEGs) identified, 214 were up-regulated and 78 were down-regulated. DEGs analysis showed that low energy X-ray irradiation could cause DNA damage and regulate oxidative stress response, amino acid synthesis, energy metabolism, virulence, and transmembrane transport in bacterial cells. These findings suggested that low-energy X-ray irradiation has the potential to inhibit bacterial growth and metabolism of cells and thereby reduce the risk of bacterial infection.