Methicillin-Resistant Staphylococcus Aureus Inactivation by Plasma Activated Water

Plasma activated water (PAW) presents an effective strategy for microbial inactivation, which is linked to synergistic effects of reactive oxygen and nitrogen species (RONS). We evaluated the antimicrobial effect of PAW against a methicillin-resistant Staphylococcus aureus (MRSA) isolated from an odontogenic abscess. S. aureus strains, and in particular MRSA strains due to their resistance, have an important role in etiology of dental abscesses. For the purpose of comparison, the reference MRSA strain routinely applied in disinfectant testing (ATCC 33591) was included in the study. The plasma source for PAW preparation was 3-pin jet using argon as the working gas (2.5 slm), with frequency of high-voltage power supply 340 kHz and applied power 14 W. Needle electrodes were inserted inside 3 separate glass tubes and positioned vertically above the water sample. We have treated 15 ml of deionized water for 10 min (pH=6.5). The PAW chemistry was characterized by colorimetric methods (H2O2 =80 ppm, NO3 - =97 ppm, NO2 - =41 ppm). Bacterial suspensions containing 10E8 cells/ml were prepared in sterile saline, and an aliquot of 100 μL per strain was added to 900 μL of PAW in microtubes. Following exposure to PAW for 15 min and 60 min, bactericidal effects were assessed by the plate count method and expressed in log CFU/mL. PAW treatment was ineffective against reference MRSA strain regardless of the exposure time. Only longer PAW treatment showed effectiveness in the clinical MRSA strain, resulting in 0.7 log CFU reduction equivalent to a 81.67% reduction in the bacterial population.