Methicillin resistant staphyloccus pseudintermedius do not develop resistance to atmospheric pressure cold plasma discharges

Summary form only given. The object of this work was to continue the study of sterilization of antibiotic resistant bacteria using the atmospheric pressure cold plasma apparatus used so successfully in St. Jude Research Hospital in Memphis, TN. The new feature in this work is reusing the surving bacteria in further tests to determine if they have acquired resistance to the plasma discharge. Acquired resistance has obviously occured during antibiotic treatment. In our plasma experiments, acquired resistance does not appear. The work was carried out in The University of Tennessee College of Veterinary Medicine. Staphylococcus pseudintermedius is the bacterium most frequently associated with canine pyoderma. The isolate used in this study, 06-3187, was obtained from a canine skin culture. It was characterized using standard biochemical methods and antibiotic susceptibility was determined using the Kirby-Bauer disc diffusion method. The isolate was determined to be resistant to oxacillin (methicillin resistant), erythromycin, penicillin, and tetracycline. It was propagated on trypticase soy agar containing 5% sheep blood (TSA) at 37 C. To determine their susceptibility to killing with atmospheric pressure cold plasma discharges, bacteria were diluted in saline tenfold from 1:10 through 1:100,000. Bacteria were added to TSA and treated in an atmospheric pressure cold plasma discharge for various periods of time. The number of surviving bacteria at each time point was: 0 min, 2.2×10⁶; 1 min, 7×10⁴; 2.5 min, 2.5×10⁴; 5 min, 2.9×10³; and 7.5 min, 3.8×10². In a separate experiment bacteria were treated for 7.5 min and surviving organisms were retested using the same conditions. Bacteria surviving the various treatments were: untreated/untreated, 3.5×10⁷; treated/untreated, 2.9×10⁷; untreated/treated, 1.2×10²; and treated/tre- ted, 2.0×10². The reduction in viable bacteria was essentially the same whether or not bacteria were previously exposed to the atmospheric pressure cold plasma discharge treatment.