Background: Plasma-activated solutions can be obtained by exposing deionized water, saline,
and citrate solution to microhollow cathode discharge. Those plasma-activated solutions showed different
temporal post-discharge effects, and those plasma-activated solutions demonstrated varied antibacterial
activity. Antibacterial activity of three types of plasma-activated solutions was investigated on Escherichia
coli (E. coli, gram-negative) and Staphylococcus aureus (S. aureus, gram-positive). Plasmaactivated
water (PAW) and plasma-activated saline (PAS) were much more potent than plasma-activated
citrate solution (PAC) as inactivating on both bacteria. Although plasma-activated solutions did not have
noticeable effects on biofilm structures, they diffused freely in biofilms and inactivated bacteria in biofilm
effectively and efficiently, resulting in bacterial cell membrane damage.
Methods: A non-thermal and microhollow cathode discharge (MHCD) device was used to generate
plasma-activated solutions. E. coli and S. aureus were used as models for antibacterial activity and antibiofilm
assay. In the antibacterial activity assay, the optical density (OD570
) of bacterial growth was
measured by using microplate reader. In the anti-biofilm assay, CV staining and MTT assay, were used to
assess biofilm susceptibility to plasma-activated solutions, and LIVE/DEAD staining kit was used to stain
and observe live and dead bacterial distributions in the biofilms and visualized by Zeiss confocal fluorescence
Results: Plasma treatments can cause the acidification of treated solutions (water and saline), but buffer
citrate solution provided sufficient buffer capacity. Although bacteria could tolerate acidic solutions prepared
from acids, they were unable to survive in plasma treated solutions after an exposure of 5 minutes
or more. More importantly, plasma-activated solutions were also inactive to biofilms and all bacteria embedded
in both one-day old biofilms (E. coil and S. aureus) were killed after 3 hours of contact time.
However, PAW and PAS are deprived of biofilm etching function. Despite completely inactivated bacteria,
PAW and PAS treated biofilms maintained the same biomass as the controls after a long incubation
time. This result supports the conclusion that different reactive species in plasma are responsible for the
antibacterial and etching activity of plasma.
Conclusion: Since plasma-activated solutions damaged bacteria by causing cell membrane lysis, they
showed low cell selectivity and were active to both gram-positive and gram-negative bacteria and
biofilms. Therefore, plasma-activated solutions can be alternates to replace chemicals, antibiotics and
antiseptics for industrial, biomedical bio-fouling applications.