The bactericidal efficacy of cold atmospheric plasma technology on some bacterial strains

Plasma, a mix of ionized gas molecules and free electrons, is often referred to as the fourth state of matter. There are different applications of plasma in our life starts from easy lighting to disease fighting and it’s nothing new. Fluorescent lights, air conditions and plasma televisions use it. One of its different types is atmospheric cold plasma, the possible applications for sterilization using cold plasmas range from the food industry to planetary space missions. The same technique could also be used on space craft leaving Earth to avoid transporting micro-organisms from Earth to other planets or moons.
The use of toxic chemicals to sterilize medical instruments may soon be a thing of the past because the use of cold plasma to sterilize heat-sensitive reusable medical tools in a rapid, safe, and effective way is bound to replace the present method which uses a toxic gas as ethylene oxide, in addition to its use for air purification. Lately it is tested to prepare surfaces for bonding and kill bacteria on delicate living tissues.
We report the results of an interdisciplinary collaboration formed to assess the sterilizing capabilities of the cold atmospheric plasma. This newly-invented source of plasma is capable of operating at atmospheric pressure in air and other gases, and of providing antimicrobial activity at room temperature as judged by viable plate counts. Plasma exposures have reduced log numbers of three tested bacterial strains namely, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa seeded on solid surfaces of Muller-Hinton agar at room temperature. Initial experimental data showed ≥5 log₁₀ CFU reduction of bacteria when 5×10⁶ cfu.ml^-1 of samples seeded on MHA plates. Results showed >5 log₁₀ CFU reduction with E. coli when exposed for up to 360 sec to plasma while the same exposure time was required for 5 log₁₀ CFU reduction killing with S. aureus samples, the least affected by this treatment was Pseudomonas aeruginosa cell suspensions where there was a very few reduction in number of survivals (≤ 10% of the whole population) after the same exposure time application. For all microorganisms tested, a biphasic curve was generated when the number of survivors versus time was plotted in dose-response curves.
In conclusion we can report that the atmospheric cold plasma generated by this method has proven sterilization (kill) capability against both gram-positive and gram-negative bacteria in different extents depending on special strain characteristics.