Use of a one atmosphere uniform glow discharge plasma to kill a broad spectrum of microorganisms

The medical, industrial, and food processing industries are constantly in s earch of new technologies to provide improved methods of sterilization and pasteurization. Proposed techniques must deal with such problems as thermal sensitivity and destruction by heat, formation of toxic by-products, cost, and inefficiency in performance. We report results from a newly invented p lasma source, a one atmosphere uniform glow discharge plasma (OAUGDP), whic h is capable of operating at atmospheric pressure in air and providing anti microbial active species at room temperature. OAUGDP exposures have reduced log numbers of bacteria (Escherichia coli, Staphylococcus aureus, and Pseu domonas aeruginosa), bacterial endospores (Bacillus subtilis and Bacillus p umilus), and various yeast and bacterial viruses on a variety of surfaces. These surfaces included polypropylene, filter paper, paper strips, solid cu lture media, and glass. Experimental results showed at least a greater than or equal to 5 log(10) colony forming units (CFU) reduction in bacteria wit hin a range of 15-90 s of exposure, whether the samples were exposed in con ventional sterilization bags or exposed directly to the plasma. An exceptio n to these very short exposure times were experiments with solid culture me dia in which 5 min of plasma exposure was necessary to produce greater than or equal to 5 log(10) CFU reduction in bacterial counts. The effects of pl asma treatment on bacterial cell structures were investigated by exposing c ells to plasma for various durations and examining them by transmission ele ctron microscopy. The results showed that cell breakage (lysis) occurred wi th the release of cellular contents. These data were consistent with spectr ophotometric results in: which the release of cellular constituents was mea sured as a change in ultraviolet absorption at 260 nm. With all microorgani sms tested, a biphasic survival curve (logarithmic number of survivors vers us time) was observed in plots of dose-response data. Differences in suscep tibilities of microorganisms observed on various surfaces suggested that th e degree of lethality was dependent upon the time of diffusion of active sp ecies through the medium to the organism and the makeup of the microbial ce llular surface. (C) 1999 American Vacuum Society. [S0734-2101(99)09904-2].