Investigating the effects of microwave plasma on bacterial cell structures, viability, and membrane integrity

Plasma-mediated bacterial inactivation holds great promise but presents several challenges. This study investigates the antibacterial effect of 2.45 GHz non-thermal microwave (MW) plasma on Staphylococcus aureus (S. aureus) and Salmonella abony (S. abony) suspended in phosphate-buffered saline (PBS). A 6-log reduction in both bacterial strains was achieved within 300 s of plasma exposure. The enhanced inactivation is attributed to elevated levels of reactive oxygen species (ROS), particularly ^·OH (30.30% in S. aureus, 40.13% in S. abony) and H₂O₂ (173.27% in S. aureus, and 391.84% in S. abony), which caused oxidative stress and membrane depolarization, detected via fluorescence spectrofluorometry. Morphological changes were confirmed through field emission scanning electron microscopy (FE-SEM). Membrane impairment led to leakage of intracellular contents such as proteins, lipids, and nucleic acids. DNA damage was evident from hyperchromic effects observed at 260 nm. Confocal microscopy revealed a qualitative increase in red fluorescent (dead) cells with longer exposure. Flow cytometry further quantified the dead cells at 88% in S. aureus and 95% in S. abony. These findings provide comprehensive insight into the bacterial inactivation mechanism and demonstrate the strong potential of non-thermal MW plasma for applications in sterilization, infection control, and food safety.