Inactivation of foodborne pathogens using a one atmosphere uniform glow discharge plasma

This study was conducted to determine the efficacy of a one atmosphere uniform glow discharge plasma (OAUGDP) for inactivation of foodborne pathogens and to evaluate the influence of growth temperature, pH, and culture age on their inactivation. Escherichia coli O157:H7, Listeria monocytogenes, Staphylococcus aureus, Bacillus cereus, Salmonella Enteritidis, Vibrio parahaemolyticus, Yersinia enterocolitica, and Shigella flexneri were evaluated. Three-strain mixtures of each bacterium were inoculated (6-7 log CFU/cm(2)) onto microscope slides containing nonselective agar media adjusted to pH 5 or 7. Samples were exposed to plasma for 0-240 sec immediately, or after incubation for 24 h at 10 degrees C or 35 degrees C. After exposure, the agar was removed from the slides and pummeled in 0.1% peptone water with a stomacher, serially diluted, surface plated onto nonselective media, and incubated at 35 degrees C. Exposure time, pH, incubation temperature, and culture age affected survival of all pathogens exposed to plasma (P < 0.05). The greatest reduction of pathogens generally occurred during the initial exposure time of 30 or 90 sec. Pathogens incubated for 24 h before exposure were more resistant than those exposed immediately after inoculation. Incubation at 35 degrees C before exposure resulted in greater resistance to plasma inactivation than incubation at 10 degrees C. No appreciable differences between gram-positive and gram-negative pathogens were observed, although the spore-forming B. cereus was more resistant to plasma than non-spore-formers. These findings support the potential for plasma treatment of foods or surfaces for pathogen reduction. Increased sensitivity of pathogens to plasma at reduced pH and temperature is encouraging, since these conditions are applicable to many foods during processing, handling, and storage.