Bacteria are central players in the development of infections, and eradicating specific pathogenic bacteria without an effect on normal mammalian tissue cells still remains a major challenge in medicine. Traditional anti-microbial approaches use antibiotics, UV photons, or nanoparticles, but they all have shortcomings like low efficacy of some specific bacteria such as antibiotic–resistant bacteria . Cold atmospheric plasma (CAP) has come into the spotlight as an effective alternative to traditional antibiotics for non-systemic infections, as plasma treatment shows remarkable effectiveness against a range of microorganisms, even including antibiotic-resistant biofilm-forming strains and spores .
All four bacterial suspensions (Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Staphylococcus epidermidis) at log phase were prepared in fresh TSB and each was diluted to an optical density equivalent to 5*106 CFU/ml. Aliquots (20μl) from each standardized bacterial suspension were exposed to the cold plasma plume for 0s, 30s, 60s, 120s, and 180s at a distance of 12 mm between the sample and the end of cold plasma jet tube. After plasma exposure, each sample was transferred to 90μl of fresh PBS and the resultant suspensions were used for determining cell viability using the colony count method. For gram-positive bacteria, they were further diluted 10 times before putting them on agar plates, while gram-negative bacteria were diluted 100 times before putting them on agar plates. Volume loss caused by evaporation during CAP treatment was assessed around 10μl, which was not considered to affect the surviving cell number.
RESULTS AND DISSCUSSION
The increasing CAP exposure time resulted in a continuous reduction in the viability of bacteria. Any of fthe our bacterial species were sufficient to achieve 80% deduction after exposure to CAP for 3 min. Interestingly, the Gram-positive species like S. aureus and S. epidermidis were less susceptible to CAP mediated bactericidal activities compared with the two Gram-negative species (E. coli and P. aeruginosa). The antimicrobial activity for the two Gram-positive species of S. aureus and S. epidermidis were 83.4% and 80%, respectively, when exposed under CAP for 3 minutes, while the two Gram-negative species E. coli and P. aeruginosa were around 95% with the same treatment. In addition, the most susceptible bacteria to CAP for 3 minutes was P. aeruginosa. Furthermore, another difference between Gram-positive and Gram-negative species is that Gram-positive species decreased at 30s then slightly increased at 60s, whereas Gram-negative showed the opposite trend with the same treatment.
This study showed that CAP is an effective method to prevent bacterial infection. The Gram-positive species were less susceptible to CAP mediated bactericidal activities compared with the two Gram-negative species.
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This study was supported by Northeastern University. Dr. Hilal Yazici is supported by TÜBİTAK (The Scientific and Technological Research Council of Turkey) – BİDEB (Programme Number: 2219).
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