Uncovering the inactivation kinetics of Escherichia coli in saline by atmospheric DBD plasma using ATR FT-IR

Plasma-liquid interactions play an important role in plasma-mediated bacterial inactivation. Attenuated total reflectance Fourier-transform infrared (FT-IR) spectroscopy is employed to probe the molecular changes occurring in Escherichia coli suspension during the direct plasma treatment and subsequent after-charge storage. The recorded spectra are correlated to the germicidal effect. Successive changes in protein secondary structures and DNA conformation are observed. It is found that spectral range around 1,345 cm(-1) is most susceptible to plasma. With respect to after-charge storage, it is shown that the cell debris is mainly composed of DNA/RNA and nitric acids with fewer proteins, and the leakage of cell inclusions becomes more severe with longer plasma treatment time. Morphology alteration revealed by transmission electron microscopy suggests cell membrane injuries and cell leakage, consistent with the FT-IR results. All these findings indicate that cell membrane damage may be the principal cause of plasma-induced inactivation.