Effect of Humidity on the Inactivation of Bacillus Subtilis Spore by Non-thermal Atmospheric Air Plasma
Authors:   School of Electrical Engineering, Dalian University of Technology, Dalian, Liaoning Province, China, Li Haiyu , Zhou Zhenyu ,   School of Electrical Engineering, Dalian University of Technology, Dalian, Liaoning Province, China, Liu Dongping ,   School of Electrical Engineering, Dalian University of Technology, Dalian, Liaoning Province, China, Cui Yunqiu ,   School of Electrical Engineering, Dalian University of Technology, Dalian, Liaoning Province, China, Sun Yuan ,   School of Electrical Engineering, Dalian University of Technology, Dalian, Liaoning Province, China, Li Jiaxin ,   School of Electrical Engineering, Dalian University of Technology, Dalian, Liaoning Province, China, Wang Yiming ,   School of Electrical Engineering, Dalian University of Technology, Dalian, Liaoning Province, China, Wang Zhishang ,   School of Electrical Engineering, Dalian University of Technology, Dalian, Liaoning Province, China, Zhao Zhiguo ,   School of Electrical Engineering, Dalian University of Technology, Dalian, Liaoning Province, China, Lu Na ,   School of Electrical Engineering, Dalian University of Technology, Dalian, Liaoning Province, China
Published: August 2023

Objective: If a medical device is not properly disinfected, it will pose a potential danger to patients. Spore is an experimental strain to verify the effect of disinfection on medical devices. It has a complex structure and is somewhat resistant to conventional disinfection techniques. Based on the advantages of simple structure and abundant reactive oxygen and nitrogen species (RONS), surface dielectric barrier discharge (SDBD) has been used to deal with inactivate spores, which provided experimental support for the application of sterilization spores in medical devices. Methods: The sterilization efficiency of the plasma was evaluated by calculating the number of viable colonies on Tryptose Soya Agar. RONS including ozone, nitrogen oxides and other reactive species produced in SDBD were measured by ozone analyzer, Fourier infrared spectrometer and chemical probes, respectively. Ultraviolet-visible spectrophotometer was used to determine the concentration of protein and nucleic acid. Results: After 20min of SDBD treatment, the number of inactivated spores could reach more than 4 log at high humidity (>6g/m3), while the spores were hardly inactivated at low humidity (<6g/m3). Ozone production was inhibited with increasing humidity while OH radicals and peroxynitrous acid increased with increasing humidity. The optical density values of protein and nucleic acid released from spores treated with SDBD was detected and a strong correlation was found with the spore inactivation trend. The protein shell and membrane structure of the spores were destroyed by SDBD, and more leakage and destruction of proteins and nucleic acids in the spores were obtained under the high humidity. Conclusion: With the increase of air humidity (from 0.15g/m3 to 70.16g/m3), stable SDBD is obtained showing a typical filamentous discharge pattern. Compared with low humidity, high humidity is more favorable to SDBD inactivation of spores.