Investigating the Role of Active Air Ions and Hydroxyl Radicals on the Eradication of ESKAPE Bacteria Using Non-Equilibrium Atmospheric Air Cold Plasma

Multidrug-resistant bacteria are becoming more common in clinical settings and are posing an increasing threat to hospitals across the globe. Considering their prevalent antibiotic resistance, the ESKAPE bacteria (i.e., Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) are becoming a serious threat to public health and are the often cause of nosocomial infections. This study uses an in-house-developed non-equilibrium atmospheric air cold plasma (NE-AACP) source to eradicate ESKAPE bacteria in an enclosed environment. The antimicrobial properties of NE-AACP source arise from the generation of negative and positive air ions (in the range of 300–<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.5\times 10{^{{5}}}$ </tex-math></inline-formula> ions/cc) and on-site generated hydroxyl radicals (in the range of 15–<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$75~\mu $ </tex-math></inline-formula>M). These quasi-static equilibrium charges disrupt bacterial cell structures and metabolic processes. The ozone concentration generated from the NE-AACP source has also been measured and found to be 0.13 ppm, which is very low for bactericidal applications. The on-site generation of hydroxyl radicals is due to the plasma-produced highly energetic electrons (3–5 eV) and coating of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mathrm { TiO}}_{2}$ </tex-math></inline-formula> nanoparticle catalysts onto one of the electrodes of the NE-AACP source. In 60 min of treatment, more than 99.9% ESKAPE bacterial inactivation has been achieved in an enclosed environment of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim ~28.3$ </tex-math></inline-formula> m3. This work elucidates the mechanism of cold plasma-induced bacterial inactivation and highlights its potential as a viable strategy against infections that are resistant to antibiotics. These findings have implications for infection control in healthcare facilities and other settings where ESKAPE bacteria provide a health concern to the general public.