Purpose: The purpose of this study was to compare the transcriptomic response of Salmonella cells to successive rounds of plasma treatment with surface dielectric barrier discharge (SDBD) actuators.
Methods: Culture suspensions of Salmonella enterica subsp. enterica serovar Enteritidis were spot inoculated onto sterile glass cover slips and treated with SDBD cold plasma actuators for four minutes at one cm for five successive times. The treated and untreated control samples were washed by vortexing in sterile peptone and the resulting wash fluid suspension was used for total RNA isolation, cell enumeration, and evaluation of bacterial inactivation. rRNA-depleted libraries of isolated RNA were sequenced and transcriptomic differences between control and treated samples were evaluated.
Results: Bacterial inactivation rates were not significantly different (P≤0.01) for all five treatments. Among 1,136 differentially expressed genes with fold changes greater than 1.50 (P≤0.01, FDR≤0.05), 492 were up-regulated (1.50 to 6.06-fold) and 644 were downregulated (-1.50 to -241.14-fold). Downregulated genes were associated with nutrient uptake, osmoregulation, alternative carbon and nitrogen source utilization, transcription, translation, and DNA damage repair. The major upregulated genes included those encoding pathogenicity associated proteins. Rapid cell lysis and lipid peroxidation caused a reduction in overall cellular stress by alleviating nutrient, osmotic, and desiccation stress.
Significance: No significant differences in bacterial inactivation rates or differential gene expression were identified that could potentially lead to resistance development. Cold plasma treatment may be a viable technology for food decontamination.