Sterilization method using plasma discharge against biofilm-producing Pseudomonas aeruginosa on surface of contact lens

Pseudomonas aeruginosa is the main causative bacteria of contact lens (CL)-associated microbial keratitis. Generally, multi-purpose solutions (MPSs) are widely used for washing, disinfection, and storage of CLs. However, the sterilization effect of an MPS against biofilm-producing P. aeruginosa is insufficient. The aim of the present study is to evaluate the bactericidal effect against biofilm-producing P. aeruginosa on CLs using plasma discharge. The standard strain of P. aeruginosa, PAO1, was used to make a biofilm-formed contamination model. The bactericidal effect of five MPSs and plasma discharge against biofilmproducing P. aeruginosa was observed using the culture method, scanning electron microscopy, and fluorescence microscopy. Plasma discharge was produced for 3, 5, or 10 min. Temperature, pH, and the concentrations of ozone (O₃), hydrogen peroxide (H₂O₂), and nitrogen dioxide (NO₂) in the discharged water were monitored. None of the tested MPSs showed a bactericidal effect after 4 h. In contrast, biofilm-producing P. aeruginosa strains were sterilized within 10 min using plasma discharge. Moreover, it was confirmed using fluorescence microscopy that there was no viable bacterium on the surface of the contamination model irradiated for 10 min. Although the concentration of O₃ was 5 ppm after 3 min of discharge, it gradually decreased subsequently. Both NO₂ and H₂O₂ concentrations gradually increased. Water temperature rose from 18 to 45°C, and pH changed from 6 to 2. The results show that plasma discharge may be effective for the sterilization of biofilm-producing P. aeruginosa on CLs.